RHEOLOGICAL, TEXTURAL, AND SENSORY EVALUATION OF TEXTURE-MODIFIED RICE PORRIDGE FOR PATIENTS WITH DYSPHAGIA

YONG HUI YIN

UNIVERSITI SAINS MALAYSIA

2019

RHEOLOGICAL, TEXTURAL, AND SENSORY EVALUATION OF TEXTURE-MODIFIED RICE PORRIDGE FOR PATIENTS WITH DYSPHAGIA

by

YONG HUI YIN

Thesis submitted in fulfillment of the requirements for the degree of Master of Science

August 2019

ACKNOWLEDGEMENT

I want to take this opportunity to express my profound gratitude and sincere regards to my main supervisor, Dr. Syahariza Zainul Abidin for her patient, encouragement, and support. Her guidance helped me throughout this research and writing of this thesis. I would also like to extend my gratitude to my co-supervisors,

Dr. Norazatul Hanim Mohd. Rozalli and Dr. Norsila Abdul Wahab provided their advice and expertise in making this research a success.

I gratefully acknowledge the support provided by Malayan Sugar Manufacturing

(MSM) Malaysia Holdings Berhad and Kuok Foundation for awarding me the fellowship to pursue this Master Degree. It would not have been possible without financial support from them. My sincere thanks also go to staff and patients in Hospital

USM, Kelantan that allowing me to conduct the sensory evaluation test. I want to give special thanks to a speech-language pathologist (Mr. Izzat Ismail) for his supervision and students from USM Speech Pathology programme for their assistance throughout the sensory data collection process. To all lecturers and laboratory assistants from the

School of Industrial Technology, thank you for helping me in accomplishing my research.

I truly appreciate to have a great supporter and motivator, Rumaisa Nordin, to help me went through all the tough time and listen to me when I needed someone to talk. Not forgetting to my fellow friends, Syuzeliana, Yong Yi, Sook Yee, Nuraihan,

Syazana, and the rest from the postgraduate room for their continuous help and moral support during the entire course of this research. Last but not least, I would like to dedicate my heartiest appreciation to my family members for their blessings, love, understanding, and motivation who made my research success.

ii TABLE OF CONTENTS

ACKNOWLEDGEMENT ...... ii

TABLE OF CONTENTS ...... iii

LIST OF TABLES ...... vii

LIST OF FIGURES ...... ix

LIST OF SYMBOLS ...... xi

LIST OF ABBREVIATIONS ...... xii

ABSTRAK ...... xiii

ABSTRACT ...... xv

CHAPTER 1 - INTRODUCTION

1.1 Background and Rationale of Study ...... 1

1.2 Objectives ...... 3

CHAPTER 2 - LITERATURE REVIEW

2.1 Dysphagia ...... 5

2.1.1 Prevalence of Dysphagia ...... 7

2.1.2 Signs and Symptoms of Dysphagia ...... 8

2.1.3 Management of Dysphagia ...... 9

2.2 Texture-Modified Food ...... 10

2.2.1 Existing Standards of Texture-Modified Food ...... 11

2.3 Thickening Agent ...... 15

2.3.1 Starch ...... 16

2.3.1(a) Physicochemical Properties of Starch ...... 17

2.3.1(b) Applications of Starch in Foods...... 19

iii 2.3.2 Gum ...... 20

2.3.3 Commercial Thickener for Dysphagia ...... 22

2.4 Characterization of Pureed Food ...... 24

2.4.1 Line Spread Test ...... 24

2.4.2 Rheological Measurements ...... 27

2.4.2(a) Rheological Measurements on Thickened Beverages ...... 29

2.4.2(b) Rheological Measurements on Dysphagia-Oriented Pureed Food ...... 30

2.4.3 Textural Measurements ...... 31

2.4.4 Sensory Evaluation ...... 34

CHAPTER 3 - EVALUATION OF PUREED RICE PORRIDGE PREPARED BY USING DIFFERENT STARCHES AND GUMS

3.1 Introduction ...... 37

3.2 Materials and Methods ...... 37

3.2.1 Materials ...... 37

3.2.2 Sample Preparation ...... 37

3.2.3 Line Spread Test (LST) ...... 38

3.2.4 Rheological Measurements ...... 39

3.2.5 Textural Measurements ...... 40

3.2.6 Statistical Analyses ...... 40

3.3 Results and Discussion ...... 41

3.3.1 Line Spread Test ...... 41

3.3.2 Flow Behavior Test ...... 43

3.3.3 Oscillatory Frequency Sweep Test ...... 46

3.3.4 Textural Measurements ...... 48

3.4 Conclusion ...... 50

iv CHAPTER 4 - CHARACTERIZATION OF INSTANT RICE PORRIDGE: PHYSICOCHEMICAL, RHEOLOGICAL, AND TEXTURAL ANALYSES

4.1 Introduction ...... 51

4.2 Materials and Methods ...... 52

4.2.1 Preparation of Instant Rice Porridge ...... 52

4.2.2 Analyses on Instant Rice Porridge ...... 52

4.2.2(a) Moisture Content and Water Activity ...... 52

4.2.2(b) Swelling Power and Solubility ...... 52

4.2.2(c) Bulk Density (Tapped Density) ...... 53

4.2.2(d) Pasting Properties ...... 53

4.2.3 Analyses on Reconstituted Instant Rice Porridge ...... 54

4.2.3(a) Line Spread Test ...... 54

4.2.3(b) Rheological Measurements ...... 54

4.2.3(c) Textural Measurements ...... 55

4.2.3(d) Effect of Salivary Amylase ...... 55

4.2.4 Statistical Analyses ...... 56

4.3 Results and Discussion ...... 56

4.3.1 Analyses on Instant Rice Porridge ...... 56

4.3.1(a) Moisture Content and Water Activity ...... 56

4.3.1(b) Swelling Power and Solubility ...... 58

4.3.1(c) Bulk Density (Tapped Density) ...... 60

4.3.1(d) Pasting Properties ...... 62

4.3.2 Analyses on Reconstituted Instant Rice Porridge ...... 65

4.3.2(a) Line Spread Test ...... 65

4.3.2(b) Flow Behavior Test ...... 67

4.3.2(c) Oscillatory Frequency Sweep Test ...... 69

4.3.2(d) Textural Measurements ...... 71

v 4.3.2(e) Effect of Salivary Amylase ...... 73

4.4 Conclusion ...... 76

CHAPTER 5 - SENSORY EVALUATION OF INSTANT RICE PORRIDGE AMONG PATIENTS WITH DYSPHAGIA

5.1 Introduction ...... 77

5.2 Materials and Methods ...... 77

5.2.1 Participants ...... 77

5.2.2 Samples and Preparation ...... 78

5.2.3 Procedures ...... 78

5.2.4 Statistical Analyses ...... 79

5.3 Results and Discussion ...... 79

5.3.1 Correlation between Sensory Attributes ...... 79

5.3.2 Correlation between Sensory Attributes and Instrumental Measurements ...... 82

5.4 Conclusion ...... 87

CHAPTER 6 - CONCLUSION AND RECOMMENDATIONS

6.1 Conclusion ...... 88

6.2 Recommendations ...... 89

REFERENCES ...... 90

APPENDICES

LIST OF PUBLICATIONS

vi LIST OF TABLES

Page

Table 2.1 Classification of texture-modified food from selected countries (Cichero et al., 2013) ...... 13

Table 2.2 Characteristics of pureed food (Level 4) according to IDDSI framework (International Dysphagia Diet Standardization Initiative, 2017) ...... 15

Table 2.3 Morphological and physicochemical properties of starches from different botanical sources (Karim et al., 2008; Murphy, 2000; Waterschoot et al., 2015a) ...... 17

Table 2.4 Categorization of dysphagia-oriented foods by LST and viscosity measurements (Paik et al., 2004) ...... 26

Table 3.1 Recipe used for the preparation of pureed rice porridge ...... 38

Table 3.2 Flow properties of pureed rice porridges prepared by different thickeners at selected concentration over a shear rate range from 0.1 to 100/s ...... 44

Table 3.3 Storage modulus (G’), loss modulus (G’’), and tan δ at 6.28 rad/s for different pureed rice porridge samples ...... 46

Table 4.1 List of the different volume of hot water used (mL) to obtain the optimal ratio for each sample (1 g) ...... 54

Table 4.2 Compositions of artificial saliva (Hur et al., 2009) ...... 55

Table 4.3 Moisture content and water activity of different rice porridge powders ...... 57

Table 4.4 Swelling power and solubility of different rice porridge powders ...... 58

Table 4.5 Pasting properties of different rice porridge powders determined using Rapid ViscoTM Analyzer (RVA)...... 65

Table 4.6 List of suitable ratio of rice porridge powder to hot water for each sample...... 66

Table 4.7 Flow properties of reconstituted rice porridge samples prepared by different thickeners at selected ratio over a shear rate range from 0.1 to 100/s...... 67

vii Table 4.8 Changes in apparent viscosities at 50/s of different reconstituted rice porridge samples before and after addition of amylase...... 74

Table 5.1 Definitions for sensory attributes of the instant rice porridge samples (Janssen et al., 2007; Jiménez et al., 2013)...... 79

Table 5.2 Pearson’s Correlation coefficients of five sensory attributes of the developed instant rice porridge samples...... 81

Table 5.3 Pearson’s Correlation analysis on sensory attributes and instrumental measurements (rheology and texture) of the developed instant rice porridge...... 86

viii LIST OF FIGURES

Page

Figure 1.1 Overall experimental design of this study which consisted of three phases and all the analyses conducted...... 4

Figure 2.1 Normal swallowing mechanism (Garcia & Chambers, 2010)...... 6

Figure 2.2 (a) Normal swallowing - the epiglottis closed to protect airways; (b) Dysphagia - the epiglottis unable to protect airways (Spong, 2015)...... 7

Figure 2.3 Classification of dysphagia diets into eight levels according to International Dysphagia Diet Standardization Initiative (IDDSI) framework (IDDSI, 2017)...... 14

Figure 2.4 Primary structure of amylose and amylopectin in starch (Sanyang et al., 2018) ...... 17

Figure 2.5 Primary structure of xanthan gum (Sworn, 2000)...... 21

Figure 2.6 Primary structure of guar gum (Tripathy & Das, 2013)...... 22

Figure 2.7 Set up for the Line Spread Test ...... 25

Figure 2.8 Schematic illustration of the oscillatory stress sweep test used to determine the linear viscoelastic region...... 29

Figure 2.9 A representative curve of texture profile analysis (TPA) [“Overview of Texture Profile Analysis,” n.d.] ...... 32

Figure 2.10 A typical curve of texture profile analysis (TPA) (Nasaruddin et al., 2012) ...... 33

Figure 2.11 Visual analog scale (VAS) (a) Unstructured line scale; (b) Structured line scale...... 36

Figure 3.1 LST measurements of pureed rice porridges formulated with different thickeners at different concentrations...... 42

Figure 3.2 Pureed rice porridge (a) without thickener (control sample); (b) with 1% gum and 2% starch; (c) commercial product; (d) with 3% starch, 2% and 3% gum...... 42

ix Figure 3.3 Result of apparent viscosity at 50/s of pureed rice porridge samples containing different thickeners. The concentration of each thickener was selected based on the viscosity value similar to the commercial sample. Values with the same letter are not significantly different from each other at p < 0.05 level of significance...... 43

Figure 3.4 Schematic illustration of the ability of xanthan gum to form a complex aggregate in solution (Norton et al., 1984)...... 45

Figure 3.5 Textural properties (firmness and cohesiveness) of pureed rice porridges prepared by different thickeners. The letters (A-E) represented significant differences in firmness values; the letters (a-e) represented significant differences in cohesiveness values at p < 0.05...... 49

Figure 4.1 Tapped density of different rice porridge powders. Values with the same letter are not significantly different from each other at p < 0.05...... 62

Figure 4.2 (a) Control sample with water separation (ratio 1:7); (b) Control sample without water separation (ratio 1:6)...... 66

Figure 4.3 Reconstituted rice porridge with guar gum (a) Too thick for swallowing and sticky texture (ratio 1:10); (b) Not too thick and able to hold its shape (ratio 1:12)...... 66

Figure 4.4 Tan 훿 at 6.28 rad/s for different reconstituted rice porridge samples. Values with the same letter are not significantly different from each other at p < 0.05...... 70

Figure 4.5 Storage modulus (G’) at 6.28 rad/s for different reconstituted rice porridge samples. Values with the same letter are not significantly different from each other at p < 0.05...... 70

Figure 4.6 Textural properties (firmness and cohesiveness) of different reconstituted rice porridge samples. The letters (A-E) represented significant differences in firmness values; the letters (a-e) represented significant differences in cohesiveness values at p < 0.05...... 72

Figure 5.1 Mean scores of sensory attributes of the instant rice porridge samples with different thickeners among patients with dysphagia (n = 20)...... 80

Figure 5.2 Principal component plot showing relationships between sensory attributes and instrumental measurements (rheology and texture) for instant rice porridge samples developed by different thickeners...... 85

x LIST OF SYMBOLS

G’ Elastic modulus

G” Viscous modulus

δ Phase angle

σ Shear stress

γ ̇ Shear rate

K Consistency index n Flow behavior index

σoc Casson yield stress tan δ Loss tangent

xi LIST OF ABBREVIATIONS

BVA Brabender Viscoamylograph

FDA Food and Drug Administration

FEES Fiberoptic Endoscopic Evaluation of Swallowing

IDDSI International Dysphagia Diet Standardization Initiative

LST Line Spread Test

LVR Linear Viscoelastic Region

NDD National Dysphagia Diet

PCA Principal Component Analysis

RVA Rapid Visco Analyzer

SAOS Small Amplitude Oscillatory Shear

SD Standard Deviation

TPA Texture Profile Analysis

VAS Visual Analog Scale

VFSS Videofluoroscopic Swallowing Study

xii PENILAIAN REOLOGI, TEKSTUR, DAN SENSORI TERHADAP PRODUK

BUBUR NASI TERUBAH SUAI TEKSTUR UNTUK PESAKIT DISFAGIA

ABSTRAK

Disfagia ditakrifkan sebagai kesukaran atau ketidakupayaan menelan makanan atau cecair. Makanan puri merupakan salah satu kategori makanan yang terubah suai tekstur dan selalu digunakan untuk pengurusan disfagia. Pesakit disfagia boleh mendapat manfaat daripada prekripsi diet ini kerana ia hanya memerlukan penyediaan dan manipulasi oral yang minima. Setakat ini, hanya beberapa kajian mengkhusus kepada reologi makanan puri berbanding minuman yang telah dipekatkan untuk pesakit disfagia. Pemekat komersial ditambah semasa penyediaan makanan puri bagi mendapatkan konsistensi makanan yang diperlukan supaya risiko tercekik dapat dikurangkan. Bagaimanapun, kos yang tinggi dan ketersediaan yang terhad bagi pemekat komersial menjadi beban kepada segelintir pesakit. Oleh itu, kajian dijalankan untuk menilai kesan penambahan kanji (ubi kayu dan sagu) dan gam

(xantan dan guar) menggunakan kepekatan yang berbeza (1, 2, dan 3% berdasarkan jumlah berat ingredien) terhadap ciri-ciri reologi dan tekstur puri bubur nasi. Sampel puri bubur nasi dengan penambahan 1% gam dan 2% kanji menghampiri kelikatan sampel rujukan (bubur nasi komersial untuk pesakit disfagia). Semua sampel puri dengan kelikatan yang sama menunjukkan ciri reologi dan tekstur yang berbeza.

Selepas pemilihan kepekatan yang sesuai bagi setiap bahan pemekat (1% gam dan 2% kanji), sampel puri bubur nasi dikeringkan dengan menggunakan pengering udara panas (80°C selama 3 jam) untuk menghasilkan bubur nasi segera. Produk yang dihasilkan dianalisa untuk sifat fizikokimia, pempesan, reologi serta tekstur. Selain itu, kajian dijalankan ke atas kesan enzim amilase

xiii dari air liur terhadap kelikatan bubur nasi segera yang telah dibancuh semula.

Kajian ini mendapati bahawa setiap pemekat mempunyai kesan sinergis yang tersendiri terhadap bubur nasi segera. Bubur nasi segera yang mengandungi gam menunjukkan ciri-ciri seperti kuasa pembengkakan, kelarutan, kelikatan puncak, breakdown, dan rintangan terhadap enzim amilase dari air liur yang lebih tinggi tetapi lebih rendah bagi ketumpatan pukal, suhu pempesan, dan kepejalan berbanding dengan bubur nasi segera yang mengandungi kanji. Penilaian sensori bagi bubur nasi segera telah dijalankan di kalangan pesakit disfagia (n=20). Analisis statistik menunjukkan penerimaan keseluruhan sampel bubur nasi adalah berkadar negatif terhadap kelekatan dan keupayaan menelan. Keseluruhannya, kajian ini berjaya menghasilkan bubur nasi segera yang sesuai digunakan di kalangan pesakit disfagia dan penerimaan dibuktikan melalui penilaian sensori. Gam xantan menunjukkan potensi yang tinggi untuk digunakan sebagai bahan pemekat bagi bubur nasi segera.

Kejayaan terhadap penggunaan gam xantan ke dalam bubur nasi segera mampu menggantikan pemekat komersial di pasaran dan mengurangkan beban kewangan pesakit.

xiv RHEOLOGICAL, TEXTURAL, AND SENSORY EVALUATION OF

TEXTURE-MODIFIED RICE PORRIDGE FOR PATIENTS WITH

DYSPHAGIA

ABSTRACT

Dysphagia is defined as the difficulty or inability to swallow food and liquid.

Pureed food, a class of texture-modified food is commonly used in dysphagia management. Patients with dysphagia can benefit from this diet prescription because it requires minimal oral preparation and manipulation. To date, only few studies focused on the rheological properties of dysphagia-oriented pureed foods compared to thickened beverages. During the preparation of pureed food, commercially available thickener is usually added to impart desired consistency, which aids in reducing the risk of choking. However, high cost and limited availability of commercial thickener are burden for some patients. Therefore, this study was carried out to evaluate the effects of different starches (tapioca and sago) and gums (xanthan and guar) at different concentrations (1, 2, and 3% based on total weight of ingredients) on rheological and textural properties of pureed rice porridge. The thickening of pureed rice porridge with 1% gum and 2% starch produced samples with close apparent viscosity to the reference sample (commercial dysphagia-oriented rice porridge product). All pureed samples with similar viscosity showed variation in behaviors during rheological and textural measurements. After selection of suitable concentration for each thickener (1% gum and 2% starch), the pureed rice porridge samples were then dried using hot air dryer (80ºC for 3 hours) to produce instant rice porridges. The developed products were tested for their physicochemical, pasting, rheological, and textural properties. Besides, the effect

xv of salivary amylase on the viscosity of the reconstituted rice porridge samples was also investigated. This study illustrated that each thickener has its own synergistic effect with instant rice porridge. The instant rice porridge with gums showed higher swelling power, solubility, peak viscosity, breakdown, and higher resistance towards salivary amylase reaction, but lower in bulk density, pasting temperature, and firmness compared to instant rice porridge with added starches. Sensory evaluation of instant rice porridge samples was also conducted among patients with dysphagia (n=20). The statistical analyses revealed that overall acceptability of rice porridge samples were negatively correlated with stickiness and swallowing effort. Overall, this study had successfully developed instant rice porridge that suitable for consumption among patients with dysphagia and was proven to be accepted through sensory study. Xanthan gum was shown to have the greatest potential to be used as a thickener in instant rice porridge. The success in incorporation of xanthan gum into instant rice porridge can help to replace existing commercial thickener in the market and reduce patients’ financial burden.

xvi CHAPTER 1

INTRODUCTION

1.1 Background and Rationale of Study

Dysphagia can be defined as the difficulty or inability to swallow food and liquid. The prevalence of dysphagia had been reported as about 8% in the general population (Cichero et al., 2013). However, it is difficult to determine the overall prevalence of dysphagia in a country because it is often reported as part of other medical conditions for which the patient is being treated (Linn et al., 2015). Dysphagia can result from several conditions such as cancer, stroke, neurological disorders, and brain injury (Houjaij et al., 2009; Cichero, 2013). Dysphagia affects all age groups but it is more common among the elderly population (Bangyeekhan et al., 2010).

People with dysphagia may also encounter difficulties in controlling saliva, problems in chewing solid foods, and choking or pain during swallowing (Adeleye & Rachal,

2007). Consequently, it leads to complications such as malnutrition and dehydration due to some of the food restrictions (decreased food and fluid intake) and dietary alteration (Andersen et al., 2013; Zargaraan et al., 2013).

Dysphagia is a symptom of an underlying disease. Often, the disease has to be treated first before dysphagia can be managed successfully. However, as patients need to be fed to maintain their nutritional intake, diet modification is usually prescribed for patients as a compensatory method to manage dysphagia. Diet modification can be classified into thickened liquid and texture-modified food. Texture-modified food is usually prepared by blending, straining to remove lumps, and followed by the addition of thickener to compensate chewing difficulties and to improve patient’s safety during swallowing. Pureed food, a class of texture-modified food, is highly recommended for

1 patients with dysphagia, who may also benefit from this diet prescription because it requires minimal oral preparation and manipulation (Zargaraan et al., 2013).

To support the people with dysphagia, food industries have started to develop

(i) special type of thickener in powder form that can be used to thicken food and liquid and (ii) pre-thickened texture-modified food for convenience. However, the commercial thickener is only available at selected pharmacies and sold at high price.

There is also another issue related to the thickness consistency level during preparation of food using commercial thickener (Payne et al., 2012). Accordingly, the use of pre-thickened texture-modified food has been proposed as an alternative solution for these shortcomings. Nevertheless, the existing pre-thickened texture- modified food is very limited and only available in certain countries such as Japan and United States.

Standardization of guidelines and terminologies are necessary to deliver better treatment outcome for patients with dysphagia (Steele et al., 2015) and also facilitate the product development from the industry sector (Cichero et al., 2007). Several standards have been developed from different countries but each standard varies across countries. The terminology, labels, and the number of levels of modification used are different. The lack of objective measurement regarding the food texture and consistency is a major barrier to the diet management of patients with dysphagia. Only subjective descriptions such as the presence of visible lumps and the ability to form shape are used to classify texture-modified food into different levels. To standardize guidelines of texture-modified food, it becomes essential to understand the major factors or measures which have to be addressed for easy and safe swallowing.

In general, this study was designed to evaluate the suitability of starch and gum as a thickener in pureed rice porridge for patients with dysphagia using rheological,

2 textural, and sensory parameters with the aims to find an alternative for commercial thickener. The overall experiemnt design for this study was divided into three phases and shown in Figure 1.1. The pureed rice porridge was selected as a food model in this study. Unlike the normal rice porridge, the pureed rice porridge need to be pureed to a homogenous texture without solid pieces being noticed and followed by the addition of thickening agent to ensure the consistency of the rice porridge is suitable for patients with dysphagia. Rice porridge is comfort food that usually recommended by the doctors for patients. The texture is soft and easily digestible, hence, it is very suitable for those who are just recovering from illnesses or have weak digestion. Rice porridge also can help to increase energy intake as the carbohydrates from the rice can serve as a good energy source.

1.2 Objectives

The specific objectives of this study were as below:

i. To study the rheological and textural properties of pureed rice porridge

with the addition of starch (sago and tapioca) and gum (xanthan and

guar) as thickener

ii. To evaluate the physicochemical, pasting, rheological, textural

properties, and the effect of salivary amylase on the developed instant

rice porridge

iii. To study the sensory acceptability of instant rice porridge among

patients with dysphagia in Hospital USM, Kelantan

3 Phase 1: Development of pureed rice porridge using different thickeners

Sample Preparation

Type of thickeners : xanthan gum, guar gum, sago starch, tapioca starch

Levels of addition : 1, 2, and 3% based on total weight of ingredients

Analyses

. Line spread test (LST)

. Rheological measurements (Flow behavior and Oscillatory frequency sweep)

. Textural measurements (Back extrusion test)

*Note: only the selected formulations were used in the next phase

Phase 2: Development of instant rice porridge

Sample Preparation

Hot air dryer (80°C, 3 h)

Analyses Powder Reconstituted . Moisture content and water activity . Line spread test (preliminary) . Swelling power and solubility . Rheological measurements . Bulk density (tapped density) . Textural measurements . Pasting properties . Salivary amylase effect

Phase 3: Sensory acceptability of instant rice porridge

Location : Hospital USM, Kelantan

Participants : Adult patients with dysphagia (n=20) Test : Visual Analog Scale (VAS) Attributes : Thickness, stickiness, graininess, swallowing effort, overall acceptability

Figure 1.1 Overall experimental design of this study which consisted of three phases and all the analyses conducted.

4 CHAPTER 2

LITERATURE REVIEW

2.1 Dysphagia

Normal swallowing is a complex action which involved three different phases, namely oral, pharyngeal, and esophageal (Kim & Han, 2005) (Figure 2.1). First, the food is chewed to reduce particle size and mixed with saliva to form a bolus (Houjaij et al., 2009). In the second phase or pharyngeal phase, the bolus which transferred by the tongue to the back of the throat triggers an involuntary swallowing reflex and passes through pharynx (the canal that connects the mouth with esophagus) (Forster et al., 2011). The soft palate also elevates to close the nasopharynx and avoid nasal regurgitations (Germain et al., 2006). At the same time, the involuntary closure of the larynx by the epiglottis occurs and breathing stops for a few seconds to prevent food from entering the airway (Bangyeekhan et al., 2012). This movement also opens the upper esophageal sphincter and allows the bolus to enter the esophagus. Once the bolus passes through the upper esophageal sphincter, relaxation of pharyngeal structures begins and breathing resumes. The esophageal phase further propels the bolus down the esophagus and directed towards the stomach with the aid of muscular action called peristalsis (Bangyeekhan et al., 2010).

5 1 2

3 4

Figure 2.1 Normal swallowing mechanism (Garcia & Chambers, 2010).

Swallowing disorder, also called dysphagia can be defined as difficulty in swallowing or moving food and liquid from mouth to stomach. Dysphagia influences the safety and efficacy of swallowing function (Forster et al., 2011). Safety usually refers to aspiration or entry of food and liquid into the airways whereas efficacy relates to efficiency and speed of patient when swallowing food and liquid (Andersen et al.,

2013). For instance in Figure 2.2, there is a danger that thin liquid can flow quickly to

6 the larynx before the epiglottis closes the entrance of airway, leading to aspiration in patients with dysphagia (O’Leary et al., 2010). Dysphagia categorization usually based on the point at which the disorder occurs during the swallowing process. In general, dysphagia can be divided into two types: oropharyngeal and esophageal dysphagia

(Clavé & Shaker, 2015). Oropharyngeal dysphagia arises when patients cannot initiate a swallow (difficulty in transferring food bolus from mouth to pharynx toward the esophagus) while esophageal dysphagia results from food sticking or feel like it is stuck in the chest (difficulty to move food down the esophagus) (Aslam & Vaezi,

2013).

(a) Normal swallowing (b) Dysphagia

Figure 2.2 (a) Normal swallowing - the epiglottis closed to protect airways; (b) Dysphagia - the epiglottis unable to protect airways (Spong, 2015).

2.1.1 Prevalence of Dysphagia

The prevalence of dysphagia had been reported as about 8% of the general population, which is 590 million people worldwide (Cichero et al., 2013). According to Bhattacharyya (2014) and Adeleye & Rachal (2007), dysphagia affects up to 15 million adults in the United States and 1 in 25 people in the United States will experience swallowing problem. This swallowing disorder also affects all age groups, but it is more common among the elderly population (Bangyeekhan et al., 2010). It is

7 prevalent in between 10-38% of independent elderly (Garin et al., 2014) and 68% of elderly residents in long-term care institutions (Rosenvinge & Starke, 2005). Apart from that, dysphagia also can result from several medical conditions and it affects more than 35% of patients with stroke (Park et al., 2014), 52 to 82% of patients with

Parkinson’s disease (Newman et al., 2016), and up to 93% of patients with traumatic brain injury (Andersen et al., 2013). To the best of author knowledge, only a few studies have been reported on the prevalence of dysphagia in patients with illnesses in

Malaysia. Linn et al. (2015) reported that 39 out of 66 patients with head and neck cancer at Hospital Universiti Sains Malaysia from 2001 to 2010 had dysphagia, while

41% based on total 134 patients had dysphagia following acute ischemic stroke in a study conducted by Hamidon et al. (2006).

2.1.2 Signs and Symptoms of Dysphagia

In the presence of swallowing disorder, patients may present with a variety of symptoms such as extra effort need to chew or swallow food, a feeling that food is stuck in throat, gurgly sounding voice quality during swallowing, and difficulty in controlling saliva (Adeleye & Rachal, 2007; Kayser-Jones & Pengilly, 1999). Patients with dysphagia may also experience coughing or choking shortly after meals (Aslam

& Vaezi, 2013). If this problem left untreated, there is a danger that some people can develop aspiration pneumonia (a lung infection due to the entry of materials like food, liquid, saliva or even stomach content into the airways) (Kayser-Jones & Pengilly,

1999). In addition to aspiration, the impaired swallowing can lead to complications such as malnutrition and dehydration (Andersen et al., 2013) due to some of the food restrictions (decreased food and fluid intake) or losing eating pleasure (Zargaraan et al., 2013). The negative impact on quality of life and social participation also other

8 consequences of dysphagia (Cichero et al., 2013). Therefore, it is essential to know the symptoms of dysphagia and seek medical advice and treatment immediately if note any of these symptoms.

2.1.3 Management of Dysphagia

It is well established that speech therapists play important roles in the assessment, diagnosis, and management of people with dysphagia. There are numerous rehabilitative and compensatory strategies for the management of dysphagia. The rehabilitative method includes several oral-motor exercises of the lips, tongue, and jaw which intended to improve the efficiency of swallowing function (Forster et al., 2011).

Besides, compensatory method focus on the implementation of techniques to allow individuals to continue safe swallowing and hence to maintain their nutrition intake

(Sura et al., 2012). Compensatory strategies mainly include postural adjustments, swallow maneuvers, and diet modification (Aslam & Vaezi, 2013).

Diet modification is one of the most common compensatory methods to manage dysphagia (Andersen et al., 2013). Diet modification can be classified into thickened liquid and texture-modified food (Moret-Tatay et al., 2015). In the case of thin liquid, it is known to increase the risk of choking among patients with dysphagia because it flows too quickly and provides insufficient time for the patients to ready to engage airway closure before swallowing (Steele et al., 2015). One of common strategy to slow down the act of swallowing is to manipulate the viscosity of thin liquid by adding thickener (Cho et al., 2012). The thickened liquid tends to flow more slowly and thus enhance safe swallowing (Cichero et al., 2013). Likewise, solid food with a coarse texture like meat and rice which require mastication are not well tolerated by the patients with dysphagia and can cause trouble in swallowing

9 (Layne, 1990). In order to reduce the risk of choking, the texture of solid food is often altered such that it requires little or no chewing (Cichero et al., 2013).

Therefore, the rationales behind modifying the consistency and texture of foods or drinks are to compensate chewing difficulties and to improve safety during swallowing

(Sura et al., 2012).

2.2 Texture-Modified Food

In order to help the patients to maintain their nutritional intake, texture- modified food can be prescribed. However, Keller et al. (2012) reported that only

15-30% of long term long term care facilities (nursing homes) and 30-45% hospitals served texture-modified food for people with dysphagia. Texture- modified food is the food that has been modified physically or is a term that refers to food with soft texture or reduced particle size (Aguilera & Park, 2016). Texture- modified food often includes food that has been minced, mashed, chopped, ground, or pureed. The type of modification is highly depending on the cause and severity of swallowing problem of the patients (Cichero et al., 2007). In addition to the type of modification, it is vital to ensure that the food textures are soft, moist, homogenous, not sticky, and do not contain fibrous structures that hard to be broken to allow ease of swallowing (Cichero, 2016). The recommendation on appropriate food texture needs to be done by a speech therapist to each patient based on their screening and clinical assessment (Cichero et al., 2013). The process of clinical assessment often started with medical history taking and followed by some non-instrumental measures such as assessing oral motor and vocal function exam and swallowing test using water with different viscosities (Speyer, 2013). Further instrumental measures such as

Videofluoroscopic Swallowing Study (VFSS) and Fiberoptic Endoscopic Evaluation

10 of Swallowing (FEES) also can be taken to develop a better overall understanding of a patient’s swallowing ability (Cichero et al., 2013).

Pureed food, a class of texture-modified food, which is mechanically altered to become soft, homogenous, and smooth in texture is highly recommended to be used in dysphagia management (Cichero, 2016). Pureed food is usually prepared by blending and followed by straining to remove lumps. Patients with dysphagia can benefit from this diet prescription because it requires minimal oral preparation and manipulation (Zargaraan et al., 2013). In contrast to pureed food, more chewing effort is required for minced food due to its larger particle size

(Keller et al., 2012). Also, the formation of cohesive bolus will become difficult in minced food because the food is being cut into small pieces, which may lead to the risk of choking (Nishinari et al., 2016). Besides, thickener is also often added during the preparation of pureed food to achieve the desired consistency. According to

Hanson et al. (2012), food with increased viscosity can help to prolong oral transit time which means individuals will have more time to prepare food bolus before swallowing, resulting in safer swallowing.

Overall, texture-modified food is usually used not only to improve swallowing safety but also help to provide nutrient intake among patient with dysphagia. However, much like a medical prescription, texture-modified food needs to meet certain standards and guarantee a safe texture during preparation to ensure patient safety and to deliver better treatment outcomes (Steele et al., 2015).

2.2.1 Existing Standards of Texture-Modified Food

In Malaysia, there is still no standard for the diet management of patients with dysphagia. In contrast, several standards have been developed from different countries

11 such as Japan, Australia, Ireland, United Kingdom, and United States of America to classify dysphagia diet. However, each standard varies across countries. The terminology, labels, and the number of levels of modification used are different. In a review of Penman & Thomson (1998), they found that there was a huge variety in the degree of modification and many different texture descriptors used covering the years from 1981 to 1996. Meanwhile, 40 different names used to label texture-modified foods were identified by an American task force, as mentioned by Cichero et al.

(2007). The same authors also reported that multiple labels of texture-modified food not only causing confusion among caregivers, health professionals, and researchers, it also can bring adverse effects to the patient and even death may be an outcome. For example, two patients with dysphagia in England were reported to have died which attributed to the delivery of inappropriate food textures (“Patients choked on hospital soft food,” 2018).

Table 2.1 listed the classification of texture-modified food from different world region (Cichero et al., 2013). It is apparent that texture-modified foods are commonly classified into three to five levels, without the inclusion of regular food (food without modification). The most widely used terminologies are soft food, minced food, as well as pureed food. Only for United Kingdom, the grading of pureed food is different from other countries where pureed food is divided into two levels: Texture B (thin) and

Texture C (thick). Apart from that, the size of particles also became one of the properties that took into consideration by some countries when naming different food textures. In Australia, the recommended particle size of soft food (Texture A) is 1.5 cm whereas 0.5 cm for minced or moist food (Texture B).

In 2012, the lack of international standardized terminology and descriptors for dysphagia diet was lead to the formation of International Dysphagia Diet

12 Standardization Initiative (IDDSI) (Steele et al., 2015). IDDSI consists of a group of volunteers from different professions around the world, namely medicine, speech therapy, nursing, dietician, and food technology. The outcomes of the international standardized terminology aim to improve patient safety, as well as to reduce miscommunication between manufacturer, consumer, and professional sectors

(Cichero et al., 2017). IDDSI framework was introduced, which categorizes the dysphagia diet into eight levels where drinks are measured from Level 0 to 4 while foods are measured from Level 3 to 7 (Figure 2.3). Pureed food is classified under

Level 4.

Table 2.1 Classification of texture-modified food from selected countries (Cichero et al., 2013)

Country Terminology (least to most modified) Australia Regular Texture A Texture B Texture C Soft Minced and Smooth (1.5 cm) moist pureed (0.5 cm) Ireland Texture A Texture B Texture C Texture D Soft Minced and Smooth Liquidised moist pureed United Texture E Texture D Texture C Texture B Kingdom Fork Pre-mashed Thick Thin mashable (0.2 cm) puree puree (1.5 cm) Japan Level 5 Level 4 Level 3 Level 2 Level 1 Level 0 Normal Soft food Paste type Jelly food Smooth Smooth diet with jelly food jelly rough with food surface protein, without except protein fish and meat USA Regular Dysphagia Dysphagia Dysphagia advanced mechanically pureed (< 2.5 cm) altered (0.6 cm)

13

Figure 2.3 Classification of dysphagia diets into eight levels according to International Dysphagia Diet Standardization Initiative (IDDSI) framework (IDDSI, 2017).

However, there are limitations of IDDSI framework. The lack of objective measurements for texture-modified food is one of the drawbacks of the framework.

The characteristics of food for each level are subjective, relying on descriptions such as the presence of a visible lump, ability to form shape, ability to eat with spoon or fork, and requirement of chewing. The food testing methods also have been based on subjective methods such as (i) fork pressure test (applying a fork to the food sample to observe its behavior when pressure is applied), (ii) fork drip test (assessing whether the food sample flow through the prongs of a fork), and (iii) spoon tilt test (to determine the stickiness and cohesiveness of food sample). These testing methods can cause inherent variability due to the different levels of force applied by the individual

(Cichero et al., 2017). Therefore, the classification and descriptions of texture- modified foods depend highly on visual assessment instead of instrumental measures.

14 Using pureed food as an example, the characteristics and testing methods in IDDSI framework were listed in Table 2.2.

Table 2.2 Characteristics of pureed food (Level 4) according to IDDSI framework (International Dysphagia Diet Standardization Initiative, 2017)

Type of food Characteristics/ Descriptions  Usually eaten with a spoon or food  Cannot be drunk from a cup  Cannot be sucked through a straw  Does not require chewing  Can be piped, layered, or molded Pureed food  No lumps  Not sticky  Liquid must not separate from solid  Falls off the spoon in a single spoonful when tilted and continues to hold shape on a plate

2.3 Thickening Agent

Starch and gum have been widely used as an ingredient in food due to their thickening purpose. Food industries also rely heavily on these ingredients because they can give products certain desired taste, texture, and mouthfeel (Chen & Ramaswamy,

1999). The food industries have created some choices to support people with dysphagia. These choices can be categorized into two main groups: (1) powdered thickeners that can be added to food or liquid and (2) pre-thickened products

(Zargaraan et al., 2013). There are still limited choices of dysphagia-oriented food in the market especially in Malaysia. For instance, there is only one company

(Simply Puree) in United Kingdom that producing a range of texture-modified foods with different levels (Texture B, C, D, and E).

Both thickener and pre-thickened product for the management of dysphagia use polysaccharides as thickening agent, which generally consisting of modified starch or gum (Payne et al., 2012). These polysaccharides have been used in texture modification because of their ability to absorb water, causing an increase in viscosity.

15 As mentioned by Clavé et al. (2006), the increase in food viscosity can help to increase the safety of swallow in patients with dysphagia, but it also may impair the efficacy of swallow if the residues are increasing in the mouth (or throat). Hence, it is vital to understand the effect of thickeners on the swallowing process in patients with dysphagia. According to Saha & Bhattacharya (2010), the effects of thickening agent depend largely on the type and concentration used and the food model in which it is used. There are still multiple sources of starch or gum that have not been properly tested for their characteristics and suitability in thickening foods for dysphagia needs.

The data comparing the effects of starch and gum on safe swallowing and acceptability of patients with dysphagia are also limited in pureed food.

2.3.1 Starch

Starch is the major reserve polysaccharide in plants which composed of two polymers: amylose and amylopectin (Figure 2.4). Amylose is a linear chain of glucose units that linked together by α-1,4 glycosidic bonds which make up about 15 to 30% of starch (Srichuwong et al., 2005). Amylopectin, the dominant component (70 to

85%), has the same basic structure as amylose, but it is larger and heavily branched with α-1,6 glycosidic bonds (Jobling, 2004). These two components form the alternate layer of amorphous and crystalline in starch granule. The botanical origins for producing starches can be divided into cereal (maize, rice, and wheat), tuber (potato), root (cassava), legume (mung bean and green pea), and stem of palm (sago) (Karim et al., 2008). More than 80% of the starch production in the world market come from maize and is mostly produced in USA (Waterschoot et al., 2015a). Wheat and potato starches are mainly produced in Europe (Jobling, 2004). In Asia, cassava (or tapioca) and sago starch are mainly produced (Jobling, 2004; Singhal et al., 2008).

16

Figure 2.4 Primary structure of amylose and amylopectin in starch (Sanyang et al., 2018)

2.3.1(a) Physicochemical Properties of Starch

The composition and structure of starch granules vary between different botanical sources and variability providing starches of diverse properties and functionalities (Table 2.3).

Table 2.3 Morphological and physicochemical properties of starches from different botanical sources (Karim et al., 2008; Murphy, 2000; Waterschoot et al., 2015a)

Sources of starch Properties Rice Tapioca Sago Maize Oval, Round, Granular shape Polygonal Oval, truncated truncated polygonal Granular size (µm) 3-8 4-35 15-65 5-30 Amylose content (%) 4-29 17-20 24-31 23-28 Gelatinization 68-78 62-73 69-74 62-72 temperature (ºC) Clear cohesive, Cooked properties Opaque gel Opaque gel Opaque gel tendency to gel

Gelatinization is a phase transition of the starch granules from an ordered state to disordered state, which usually achieved by heating starch with sufficient water

(Altay & Gunasekaran, 2006). The gelatinization temperature of most starches is in

17 the range between 60 to 80ºC (Copeland et al., 2009). During gelatinization, the starch granules absorb water and start to swell. The initial swelling takes place in the amorphous regions of the granules and causes destabilization in the crystalline regions

(Hsu et al., 2000). The crystalline regions irreversibly disrupted as evidenced by a loss of birefringence (Palav & Seetharaman, 2006). Then, the amylose slowly leaches out from the swollen granules increase the viscosity of the solution.

Pasting is usually related to the development of viscosity which also involving granular swelling, leaching of molecular components from the granules, and total disruption of the granules (BeMiller, 2011). Brabender Viscoamylograph (BVA) and

Rapid Visco Analyzer (RVA) are usually used to evaluate the pasting properties of starch (Hagenimana & Ding, 2005) When the heating continues, more and more amylose molecules, as well as amylopectin, are leached out from the granules. The maximum viscosity (called peak viscosity) is achieved when the granules are fully swollen (Considine et al., 2011). The maximum viscosity is then followed by a decrease in viscosity due to the breakdown of granules and the dispersion of starch molecules in the solution (Waterschoot et al., 2015b). Several factors are affecting the rate and extent of swelling and breakdown of the starch such as the type of starch, composition of starch (for example the presence of protein and lipid), temperature, and shear force (Debet & Gidley, 2007). In general, the higher the amylose content, the lower the peak viscosity (Copeland et al., 2009). During the cooling phase, the solubilized starch polymers begin to re-associate in an ordered structure. Thiis process is called retrogradation. Then, the viscosity increased due to the formation of gel which held together by intermolecular interactions involving amylose and amylopectin molecules and known as final viscosity (Fu et al., 2015).

18 2.3.1(b) Applications of Starch in Foods

Starch is one of the most commonly used thickening agents in food. According to Copeland et al. (2009), approximately 60 million tons of starches are extracted annually worldwide from various botanical origins, and 60% are used in foods. This is because starch is considered as a natural ingredient. It is also cheap, abundant, and easily available in the market (Chantaro et al., 2013). According to Saha &

Bhattacharya (2010), the use of starch at low concentration (2 to 5%) also possibly does not contribute any remarkable taste to food. Hence, starch has been added into many foods like sauce, soup, cream-based product, and dessert (Srichuwong et al.,

2012). For instance, tapioca starch which essentially contribute minimal flavor to the food system is commonly used in pudding, fish crackers, soup, and baked goods

(Otegbayo et al., 2013). Besides, tapioca starch has been widely used in baby food as a thickener because it can provide the desired texture and stability, as well as its low flavor contribution (BeMiller & Whistler, 2009). Native tapioca starch also usually forms a clear and smooth texture when cooked (Russ et al., 2016). In addition, sago starch which is one of the native starches has been used in food for many years mainly for the production of vermicelli, bread, and biscuit (Ahmad et al., 1999). The properties of sago starch are it is easy to gelatinize, exhibit high viscosity, and low in gel syneresis (Maaruf et al., 2001). Due to these reasons, sago starch also has been used in jellies, puddings, and soups in Southeast Asia (Karim et al., 2008).

However, the use of native starch in industrial applications is limited because of its low solubility in water and low resistance towards processing conditions that involve heat, shear, and acid (Sun & Yoo, 2015). Several attempts had been carried out by researchers to improve the functional properties of starch. First, starch is subjected to physical or chemical modification to obtain the desired properties such as

19 quick dispersion in cold or hot food and higher resistance towards the processing conditions (Ashogbon & Akintayo, 2014). Secondly, with the drive towards more natural food system, mixing of starches or mixing of starch and gum is another way to improve the functional properties of native starch without modification (Arocas et al.,

2009; Waterschoot et al., 2015b). Sun & Yoo (2015) reported that the blend of rice starch with tapioca starch resulted in higher gel strength and better freeze-thaw stability. Additionally, the quality of noodles which made by blending of potato starch and rice starch was shown to improve in transparency and slipperiness (Sandhu et al.,

2010). The blends of oat, potato, and corn starch with xanthan gum also were tested in strawberry sauce and found that the sensory and texture properties of the sauce were stable for three months.

2.3.2 Gum

Gum, also known as hydrocolloid, is categorized based on its source (botanical, animal, seaweed, microbial, and synthetic) or chemical structure (glucan, protein, xylan, galactomannan, and many others) (Li & Nie, 2016). According to Li & Nie

(2016), as in 2013, the food hydrocolloid market is growing significantly and is projected to reach $8.8 billion by 2018 with North America as the largest consumer for food hydrocolloid. The main reason for the extensive use of gum as food additives is due to the presence of many hydroxyl groups in the structure that can increase their ability to bind with water.

Xanthan gum is a non-linear anionic microbial polysaccharide that produced by Xanthomonas campestris (Ahmed & Ramaswamy, 2004). The primary structure of xanthan gum composed of two glucose units, two mannose units, and one glucuronic acid (Figure 2.5). Its main chain consists of β-D-glucose units linked at the 1- and 4-

20 positions, which is the same as in cellulose (Garcı́a-Ochoa et al., 2000). Trisaccharide side chain which composed of a D-glucuronic acid unit between two D-mannose units is attached to every second glucose residue of the main chain. Xanthan gum is accepted as a safe food additive under United States Food and Drug Administration (FDA) without any specific quantity limitations and also designated by European Union as

E415 (Lopes et al., 2015). Xanthan gum has been commonly used as thickening agent and stabilizer in a wide variety of foods such as frozen foods, bakery products, juice, powder beverages, yogurt, sauces, and gravies (Lopes et al., 2015). The advantages of xanthan gum as thickener include high viscosity at low concentration, high shear- thinning behavior, and stable towards pH, temperature, and enzyme (Demirci et al.,

2014). The stability of xanthan gum can be explained through its conformation in solution where the side chain wraps around the main chain to protect the labile linkages from adverse conditions (Sworn, 2000).

Figure 2.5 Primary structure of xanthan gum (Sworn, 2000).

Guar gum is a natural and non-ionic polysaccharide which extracted from the ground endosperm of guar (Demirci et al., 2014). It is a high molecular weight

21 carbohydrate with white to yellowish white (Tripathy & Das, 2013). Guar gum molecules consist of a linear chain of β-1,4-linked mannose units with randomly attached α-1,6-linked galactose units (Figure 2.6) (Martín-Alfonso et al., 2018). Due to its low cost and ability to produce a highly viscous solution at low concentration, guar gum is widely used as a thickener and stabilizer in foods (Demirci et al., 2014).

For instance, the incorporation of guar gum in salad dressing, sauce, and canned soup able to improve product stability and appearance (Mudgil et al., 2014). The thickening process of guar gum in solution occurs when the galactose side chains interact with water molecules by forming strong hydrogen bonds between them (Tripathy & Das,

2013). Similar to xanthan gum, the FDA has approved guar gum as a food additive

(Tripathy & Das, 2013) and designated by the European Union as E412.

galactose unit

mannose units

Figure 2.6 Primary structure of guar gum (Tripathy & Das, 2013).

2.3.3 Commercial Thickener for Dysphagia

For diet management of dysphagia, a commercial thickener is usually added into food and drink. However, its availability only limited to selected pharmacies and normally sold at a higher price. At first, the commercial thickeners available in the market are mainly formulated from modified corn starch. Lotong et al. (2003) reported that there was an issue closely related to corn starch due to its strong starchy flavor thus reducing the acceptability of the thickened drinks. Garcia et al. (2005) also

22 reported that thickened liquid with modified starch was unstable where the viscosity continued to increase over time. It is undesirable because the over-thickened product may increase choking risk in people with dysphagia (Hadde, Nicholson, & Cichero,

2015).

As a result, there has been a shift toward gum-based thickener due to undesirable properties found in the starch-based thickener. Xanthan gum and guar gum are the polysaccharides that typically used in the gum-based thickener. Xanthan gum gained popularity over modified starch in thickened liquid because it possesses a range of desirable properties, such as having a better taste, more stable viscosity over time and less affected by amylase (Vilardell et al., 2016). It also eliminates grainy texture and gives smooth texture when compared to starch-based thickener (Cichero, 2013).

However, recent review by Cichero (2013) had established that gum reduces the bioavailability of medicine used, which may cause medical complications in critical patients. Gum as non-starch polysaccharides, particularly galactomannan tends to pass through, relatively untouched until the intestines. Since gum only can be digested by the gut microflora, it may cause an issue in patients receiving strong antibiotics that reduce the gut microflora. Unlike gum, starch can be broken down through all phases of digestion, starting from the mouth until further processes in the small intestine where water and nutrients are absorbed (Moret-Tatay et al., 2015).

Besides that, a number of studies have found that inconsistencies of thickness level exist when individuals make up their own thickened beverages using a commercial thickener (Adeleye & Rachal, 2007; Steele et al., 2003). This variability has been reported by Glassburn & Deem (1998) where the clinicians (even experienced speech-language pathologist) in the hospital were not consistent in their ability to thicken liquids. There are several factors that may lead to this variation include the

23 type and temperature of the beverage, thickener brand, and thickening techniques

(Pelletier, 1997). Apart from the need of standard guidelines and training to ensure consistent viscosity, Mills (1999) and Zargaraan et al. (2013) proposed that the use of pre-thickened foodstuffs is another potential alternative to overcome the shortcomings of commercial thickener.

2.4 Characterization of Pureed Food

The characteristics of pureed food after addition of thickener mostly examined through instrumental measures (rheological and textural analyses). Several testing modes and applications can be carried out by rheometer and textural analyzer to predict the effectiveness of a pureed food for swallowing among patients with dysphagia. This is because the instrumental measurements can be used to determine the structural changes during processing and molecular interactions of foodstuff (Zargaraan et al.,

2013). Besides, sensory evaluation has been developed as a scientific tool for measuring and analyzing human responses towards a product as perceived through senses of sight, smell, touch, taste, and hearing (Foegeding et al., 2011). It also plays an essential role in characterizing pureed food for patients with dysphagia because instrumental methods which often conducted under a controlled condition cannot completely explain the complex texture and sensory attributes of food (Janssen et al.,

2007). With the combination of instrumental measurements and sensory analyses, it can help to develop safe foods with desired sensory properties and at the same time increase oral and nutrient intake among patients with dysphagia.

2.4.1 Line Spread Test

Line spread test (LST) was developed in the 1940s to measure the consistency of liquid-like foods (Nicosia & Robbins, 2007). LST is an empirical test of rheology

24 to quantify the consistency of a standard amount of thickened product by measuring the distance traveled across a flat surface after the sample released from a confined chamber (Mann & Wong, 1996). It only requires a hollow cylinder, a laminated sheet of paper marked with concentric circles, and a flat surface (Figure 2.7). The sample to be tested is first placed into the hollow cylinder, and then the cylinder is lifted to allow the sample to spread for a fixed period (Dahl, 2015). This test is easy, fast, and relatively cheap to use if compared with a viscometer (Ettinger et al., 2014). The simplicity of LST also makes it one of the most popular ways to use by clinicians in measuring the thickened liquid for patients with dysphagia.

Figure 2.7 Set up for the Line Spread Test

LST has been successfully used in multiple literatures in estimating the viscosity of thickened beverage. According to Budke et al. (2008) and Paik et al.

(2004), the line spread measurements were correlated well with viscosity measured using viscometer. Nicosia & Robbins (2007) also reported that LST was able to differentiate between liquids with very different consistencies. On the other hand, only a few researchers have studied the use of LST on texture-modified food. There is still no standard has been developed for the use of LST in the evaluation of pureed food for patients with dysphagia. Paik et al. (2004) categorized dysphagia-oriented foods

25 into three levels based on LST and viscosity (measured by viscometer), as shown in

Table 2.4. Additionally, Dahl (2015) evaluated the LST measurements of pureed food together with visual inspection by looking at the thickness and absence of water separation.

Table 2.4 Categorization of dysphagia-oriented foods by LST and viscosity measurements (Paik et al., 2004)

LST (cm) Dysphagia-Oriented Foods Viscosity (Pa∙s) 0 – 1.0  Thick rice gruel > 10  Crushed potato  Cooked ground vegetable (mixed with 4.5% of thickener)  Cooked ground meat, cooked ground meat (mixed with 4.5% of thickener) 1.1 – 2.9  Cooked ground vegetable 0.1 – 9.9  Thin soup with starch  Cream soup  Thin rice gruel 3.0 – 3.9 Thick, fluid-type rice 0.01 – 0.09

One of the limitations of LST is that its measurement only can be carried out at one temperature and one holding time (Budke et al., 2008). It is challenging to control all those critical factors such as temperature changes and holding time.

Secondly, the increase in viscosity of thickened product may cause LST to limit its ability in measuring the distance of spread. This statement can be supported by a study conducted by Ettinger et al. (2014), who worked on pureed food and mentioned that the thick pureed product showed non-distinguishable readings (0 cm) using LST. This result fairly well with Park et al. (2014) who described that the thickened products showed similar LST results at high concentration although their viscosities were different.

Overall, LST may be enough to be used as a screening test to differentiate a broad category of the thickened product but cannot be used to measure viscosity

26 (Nicosia & Robbins, 2007). Hence, other instrumental analyses may require to give detail information on the rheological and textural properties of the thickened product.

2.4.2 Rheological Measurements

Rheology is the study of deformation and flow of matter, ranging from liquid

(viscous) to solid (elastic) (Wendin et al., 2010). Rheological measurements are usually used to analyze the physical properties of food samples, particularly its flow and viscoelastic behavior (Moelants et al., 2013). In most cases, rheometer is more preferred to be used for viscosity measurement compared to viscometer. The main reason is the extended applications of rheometer which allow the flow behavior of a sample over a wide range of shear rates to be studied, unlike the viscometer which only able to perform viscosity measurements at one shear rate each time. The shear rates ranged from 0.1 to 100/s are mostly used and most relevant for food texture studies (Alvarez et al., 2004). Besides, several studies also have suggested that the shear rate of 50/s to be representative of the swallowing process and as a national standard for comparing the products (Hong et al., 2012; Paik et al., 2004; Payne et al.,

2011) in spite of the normal shear rate of swallowing was estimated from 1 to 1000/s.

The shear rate of swallowing process for dysphagia patients is also not well-known because it varies with their medical conditions (Park et al., 2014).

The study of flow properties of food using rheometer able to provide specific terminologies to discuss foods as well as the mathematical reference to describe the changes of viscosity (Germain et al., 2006). For example, the rheological data (shear stress versus shear rate) of semi-solid foods are mostly fitted and described by using mathematical modeling, namely Casson and Herschel-Bulkley models (Alonso et al.,

1995). Both models provide rheological parameters such as the flow behavior index,

27 consistency coefficient, and yield stress. Most of the pureed food exhibit non-

Newtonian (shear-thinning behavior) with yield stress (Colin-Henrion et al., 2007).

The shear-thinning behavior can be defined as the decrease of viscosity with the increase of shear rate. In the opposite side, only a few fluids (honey, oil, and pure water) exhibit Newtonian behavior where the viscosity remains constant irrespective of the amount of shear applied for constant temperature. Furthermore, yield stress is another useful rheological parameter to be identified in order to prepare desirable food for dysphagia patients (Zargaraan et al., 2013). Yield stress can be defined as the minimum stress that required to initiate the flow of a sample which is relevant to swallowing action. The higher the yield stress, the higher the force needed to initiate the flow and make the swallowing process more difficult for patients with dysphagia.

Pureed food usually exhibits pronounced viscoelastic properties. In order to study the viscoelastic properties of food, small amplitude oscillatory shear (SAOS) test, also called dynamic rheological test is frequently used. SAOS test is a non- destructive technique where the sample is initially subjected to very low applied stress

(often below the yield stress of a sample) (Gunasekaran & Ak, 2000). The small stress range where the structure is not destroyed is called linear viscoelastic region (LVR)

(Figure 2.8). The length of LVR also can be used to determine the stability of a sample

(Norazatul Hanim et al., 2016). The longer the length, the higher its stability and not easily break down.

28

Figure 2.8 Schematic illustration of the oscillatory stress sweep test used to determine the linear viscoelastic region.

Once LVR is determined, an oscillatory test over a range of frequency

(frequency sweep test) can be carried out to gain insight on the internal structure of food substances (Moret-Tatay et al., 2015). The parameters that can be obtained from the oscillatory frequency sweep test include elastic modulus (G’), viscous modulus

(G”), and phase angle (δ) (Colin-Henrion et al., 2007). If G’ is larger than G”, the sample is more towards solid-like behavior. If G” is larger than G’, the sample behaves more liquid-like. Moreover, the tangent of phase angle provides information on viscoelastic properties of a sample, considering both elastic and viscous modulus (tan

δ = G”/G’) (Sharma et al., 2017). A phase angle of 90º indicates a fully viscous material whereas a fully elastic material is characterized by a phase angle value of 0º

(Ahmed & Ramaswamy, 2007).

2.4.2(a) Rheological Measurements on Thickened Beverages

There are extensive literatures that worked on the rheological properties of thickened beverages for people with dysphagia. National Dysphagia Diet (NDD) has been used exclusively as a reference in many papers related to thickened beverages.

29 This NDD guideline (NDD Task Force, 2002) categorizes thickened beverages based on their viscosity: thin (1-50 cP), nectar-like (51-350 cP), honey-like (351-1750 cP), and spoon-thick (above 1750 cP). In addition, factors that affect the viscosity of thickened beverages such as type of dispersing medium and type of thickener had been well researched (Garcia et al., 2005; Garin et al., 2014; Moret-Tatay et al., 2015; Payne et al., 2012). For example, the rheological measurements on six different thickeners were carried out in different media, namely water and cordial (Sopade et al., 2007), milk, (Sopade et al., 2008a) and fruit juice (Sopade et al., 2008b). Some of the above- cited authors also applied various rheological models to study the flow behavior of each dispersing medium or each thickener within the concentration range studied.

Moreover, other researches also studied on the effects of standing time before consumption (Dewar & Joyce, 2006b, Garcia et al., 2005) and temperature (Adeleye

& Rachal, 2007) towards viscosity of thickened beverages.

2.4.2(b) Rheological Measurements on Dysphagia-Oriented Pureed Food

The effectiveness of a pureed food for safe swallowing among patients with dysphagia is highly depending on its rheological properties. There are number of pureed foods such as infant puree (Ahmed & Ramaswamy, 2006), and fruit and vegetable-based puree (Alvarez et al., 2004; Moelants et al., 2013; Diamante & Liu,

2016) have been examined using rheological measures. However, from the literarures, only a few studies worked on the rheological properties of dysphagia- oriented pureed foods (Sharma et al., 2017) compared to thickened beverages.

Therefore, the information relating to the objective measurement of dysphagia- oriented pureed foods has been relatively scanty (Steele et al., 2015).

30 According to Zargaraan et al. (2013), most of the research on dysphagia- oriented products only focused on viscosity. Further investigation on the effect of dynamic rheological properties on swallowing of pureed food also should be carried out. This is because most of the pureed foods exhibit non-Newtonian behavior and this makes them impossible to characterize entirely with only one viscosity measurement

(Cichero et al., 2017). Additionally, the use of thickening agent not only increasing the viscosity but also gives elastic properties to the food (Payne et al., 2012).

Therefore, this leads to the explanation of why the use of a single-point viscosity measurement such as at the shear rate of 50/s provides an oversimplified view on pureed food.

Besides, Chen (2014) reported that the involvement of saliva could not be avoided in human swallowing process but often excluded in instrumental testing. The inclusion of saliva in instrumental testing is important in predicting the texture and sensory attributes especially in starch-based food (Foegeding et al., 2011). This is because starch-based foods are sensitive to salivary amylase in the saliva of mouth.

When a person eats, saliva is secreted and mixed into the bolus. Salivary amylase is known to catalyze the hydrolysis of α-1,4-glycosidic bonds in starch and thus reducing the viscosity of the thickened food (Vallons et al., 2015).

2.4.3 Textural Measurements

Texture is usually considered as the most critical quality indicator that determines the consumer acceptance of pureed food. For pureed food like porridge, firmness and consistency are the greatest important textural attributes among sensory factors (Murugkar et al., 2015). It is known that the deformation mode in the swallowing process not only involves compression or a simple flow in a uniform tube,

31 but a mixed mode consisting of more than two modes like compression and shear

(Nishinari et al., 2016). Consequently, many studies have characterized the texture of pureed food using a few instrumental analysis as well as different probes have been used. Both texture profile analysis (TPA) and back extrusion test which can perform compression mode are usually carried out using texture analyzer.

In TPA, the food sample is compressed instrumentally twice in a reciprocating motion that imitates human mastication condition (Funami, 2016). TPA is initially designed for the measurement of solid foods. It can measure multiple parameters, namely hardness, cohesiveness, adhesiveness, chewiness, resilience, gumminess, and springiness in one experiment by generating a force-time curve (Figure 2.9). For semi- solid or liquid foods, support of container or cup is needed (Funami, 2016). The same author also mentioned that TPA sometimes has its own limitations where it cannot be used to compare among samples of different viscoelastic nature. Besides, Ramaswamy et al. (2015) also reported that TPA could not be used to measure samples that are neither in liquid nor a firm gel.

Figure 2.9 A representative curve of texture profile analysis (TPA) [“Overview of Texture Profile Analysis,” n.d.]

32 Back extrusion test is one of the texture assessments that is useful for samples with high consistency or with suspension of particles. According to Ramaswamy et al.

(2015), back extrusion test able to bridge the information gap between liquid and gel type samples which means intermediate semi-solid samples are also suitable in this test. It has been used in many products such as pureed carrot (Ettinger et al., 2014), porridge (Carvalho et al., 2014), food hydrocolloids (Cevoli et al., 2013), yoghurt

(Eroglu et al., 2016) and tomato ketchup (Sit et al., 2014). Besides, back extrusion test is simple and fast (Brusewitz & Yu, 1996). The measurement started when the plunger is forced down into the sample that contained in a cylindrical cup, and then the sample flows upward through the annular place to give a force-time curve (Tawongsa &

Abdelmoula, 2014). The parameters obtained from the test consisted of firmness

(maximum or peak force obtained as a result of compression), consistency (positive area of the graph), cohesiveness (maximum negative force), and viscosity index

(negative area of the curve) (Figure 2.10).

Figure 2.10 A typical curve of texture profile analysis (TPA) (Nasaruddin et al., 2012)

33 2.4.4 Sensory Evaluation

Sensory evaluation which involves preference or acceptability of food is an essential area of research. It is imperative especially in the development of new product: (1) to evaluate the effect of new added ingredients or processing conditions on the particular product and (2) to know more about what factors that affecting the preference and acceptability of consumers towards a particular product. Since pureed food is usually modified and formulated for patients with dysphagia to be safe for swallowing, its consistency that resembles baby food in presentation makes it less appealing (Stahlman et al., 2001). It also often has unpleasant taste or mouthfeel, unlike natural foods due to the addition of the thickener. In order to increase the appeal of the food, boosting the aroma and flavor of the pureed food has been found to be one way to enhance the human sensory experience (Cichero, 2016). For instance,

Henry et al. (2009) reported that the addition of oyster sauce, ginger, and garlic could help to increase food intake among hospitalized elderly.

The sensory evaluation consists of some testing methodologies that can be used to study the intensity of food perception and acceptability among consumers (Lawless

& Heymann, 1998). To carry out sensory studies among vulnerable groups like patients with dysphagia, it is vital to take into account the appropriate testing method or scale to be used. They may encounter problem with simple testing method due to visual difficulties, hearing impairment, difficulty in writing or expressing themselves, and becoming fatigued if the sample is too many (Methven et al., 2016). For example,

Pelletier & Lawless (2003) reported that facial scale was found to be suitable in testing food preference for nursing home residents with neurogenic problem and having both reading and communication problems while the 9-point hedonic scale required less

34 time to complete and was slightly better in identifying the taste acceptance patterns if the residents possess the skills to understand the test.

In literature, the sensory data related to the rating of swallowing difficulty perception were limited. Therefore, a reliable method for sensory evaluation of swallowing difficulty remains to be established (Hayakawa et al., 2014). Numerical sensory data are needed to investigate the food texture precisely. Most of the sensory tests in previous studies used healthy or young adults as panelists (Methven et al.,

2016). Sharma et al. (2017) conducted a descriptive analysis on texture perception of pureed carrot which prepared by different hydrocolloids using nine healthy trained panelists. They reported that the sensory attributes of pureed carrots were different depending on the type and concentration of thickeners added. Ishihara et al. (2011) assessed the swallowing difficulty of food gel made by different gums by sensory test with healthy adults. They concluded that the cohesiveness and surface lubricity determine the swallowing ease of bolus, where the miscibility with saliva is crucial.

The only drawback of using healthy adults as sensory panelist is they may perceive swallowing difficulty differently from patients with dysphagia. However, training of patients with dysphagia is extraordinary challenging due to their trouble in swallowing as well as suffer unstable medical condition (Kohyama et al., 2015).

In order to measure the perceived intensity of food, the method used should be straightforward, easy to understand, and not very cognitively demanding for patients with dysphagia. Structured and unstructured line scales, also known as visual analog scale (VAS), is one of the methods that has been widely used in recent years for rating liking and quantifying the intensity of perception and swallowing difficulty of foods (Methven et al., 2016) (Figure 2.11). VAS has been used for healthy adults

(Kremer et al., 2007; Laguna et al., 2016), older patients (Seo & Hummel, 2009), and

35 patients with cognitive diseases (Sienkiewicz-Jarosz et al., 2013). For unstructured line scales, the participants will be required to rate the attributes on the 100 mm lines with descriptors labeled at both ends. The scale will be marked “Not at all” (on the left end – 0 mm) and “Extremely” (on the right end – 100 mm) for rating intensity. The

VAS score will be determined by measuring the distance on the line between the left- hand end to the point which the participant will be marking. It is easy to use because reference product standard is not essential (Methven et al., 2016). The same authors also proposed that structured scales can be used to give better guidance and improve consistency. The structured scales is presented similarly as unstructured scales, but the only difference is equal points are drawn on the 100 mm line.

Figure 2.11 Visual analog scale (VAS) (a) Unstructured line scale; (b) Structured line scale.

36 CHAPTER 3

EVALUATION OF PUREED RICE PORRIDGE PREPARED BY USING DIFFERENT STARCHES AND GUMS

3.1 Introduction

This chapter was designed to evaluate the suitability of two different starches

(sago and tapioca) and gums (xanthan and guar) as thickener for pureed rice porridge model at different level of addition using rheological and textural properties. A commercial dysphagia-oriented rice porridge product that normally used at medical institutions and nursing homes was also included as a reference.

3.2 Materials and Methods

3.2.1 Materials

Both starches (sago and tapioca) and gums (xanthan and guar) which used as thickener were obtained from Sim Company Sdn. Bhd. (Penang, Malaysia). The basic ingredients of pureed rice porridge were purchased from the local wet market in

Penang, Malaysia. A commercial dysphagia-friendly porridge product (Healthy Food

Co., Ltd., Japan) was included as a reference (Refer to Appendix A). The commercial product uses polysaccharide and edible gum as thickening agent.

3.2.2 Sample Preparation

The pureed rice porridge was prepared according to the method described by

Cheung (2014) with modification, using the ingredients as listed in Table 3.1. The rice grain was ground into powder form using dry mill blender (Model MX-GM1011H

Panasonic, Malaysia) for 1 min. The rice powder was mixed with all the basic ingredients and cooked for 12 min using steam jacketed pot (Model TDB/6, GROEN,

37 Unified Brands, Mississippi, USA). The control sample without any addition of thickener was prepared according to the procedures above. The amount of thickener used was varied between 1 to 3% based on the total weight of ingredients. For samples with thickener, the starch was added during the cooking whereas gum was dispersed on the cooked porridge and mixed by using a food processor (Model MK-5087M Panasonic, Malaysia) for 2 min after cooking. The cooked porridges were then sieved (mesh size approximately 1000 μm) immediately.

For commercial porridge product, it was prepared according to the manufacturer's instructions, where the package was boiled for 4 min in hot water. All the samples were left to cool to room temperature (25°C) prior to analyses.

Table 3.1 Recipe used for the preparation of pureed rice porridge

Ingredients Weight (g) Rice powder 20.0 Water 474.0 Salt 2.5 Onion powder 1.4 Garlic powder 0.5 Ginger powder 0.5 Black pepper 0.1 Chicken seasoning granule 1.0 Total 500.0

Amount of thickener used Starch or gum 1% 5.0 Starch or gum 2% 10.0 Starch or gum 3% 15.0 Notes: The amount of thickener used was varied between 1 to 3% (5.0-10.0 g) based on the total weight of ingredients (500 g).

3.2.3 Line Spread Test (LST)

The test was conducted using a clear glass plate (19.5 cm x 19.5 cm) laid on top of a sheet marked with concentric circles spaced 1.0 cm apart from 2.0 cm to 5.0 cm radius. The testing procedure was conducted by following the method described by Budke et al. (2008) with slight modification. The rice porridge (5 g) was poured

38 into the hollow glass cylinder (2.0 cm in diameter and 2.9 cm in height) that positioned at the center of the circles. After 10 min, the cylinder was lifted to allow the sample to spread on the glass plate for 1 min. The average measurements of LST were made based on the sample spreading at the four quadrants of the circle. This procedure was repeated three times for each sample.

3.2.4 Rheological Measurements

The rheological properties of pureed rice porridge were evaluated through both stepped flow and oscillatory frequency sweep tests using controlled stress AR 1000 rheometer (TA Instruments, New Castle, DE, USA) equipped with a temperature controller. All the measurements were carried out at 37°C using parallel plate geometry (20 mm diameter) with a gap of 1.0 mm. The sample was allowed to equilibrate for 30 s after loading on the rheometer plate. All the rheological measurements were performed in triplicate.

Stepped flow test data were obtained over a shear rate range from 0.1 to 100/s.

The apparent viscosity at 50/s, the representative shear rate for swallowing, was selected for comparison among samples (Zargaraan et al., 2013). The concentration of each thickener was selected based on the viscosity value similar to the commercial product. The data collected were then fitted to the well-known power law model

(Equation 3.1) and Casson model (Equation 3.2) to describe the rheological behavior of the samples.

휎 = 퐾훾̇ 푛 (3.1)

0.5 0.5 휎 = 퐾표푐 + 퐾푐훾̇ (3.2)

where 휎 is the shear stress (Pa), 훾̇ is the shear rate (s-1), K is the consistency

n index (Pa∙s ), and n is flow behavior index (dimensionless). Casson yield stress (휎표푐)

39 was calculated as the square of the intercept ( 퐾표푐 ) which obtained from linear regression of the square roots of shear stress-shear rate data.

Oscillatory frequency sweep test was carried out over the range from 0.1 to

10.0 Hz. The linear viscoelastic region for each sample was also determined from oscillatory stress sweep test at 1 Hz. TA Rheology Advantage Data Analysis software

(version V5.7.0) was used to determine the experimental data of storage modulus (G’), loss modulus (G”), and loss tangent (tan δ).

3.2.5 Textural Measurements

The textural properties of pureed rice porridge were determined through back extrusion test using TA-XT2 Texture Analyzer (Stable Micro Systems, United

Kingdom). Fifty-five grams of each sample was weighed into back extrusion vessel and the tests were carried out using disc plunger (diameter 35 mm) at the following settings: test speed: 1.50 mm/s, pre-test speed: 1.00 mm/s, post-test speed: 10 mm/s, distance: 15 mm, and return distance: 65 mm. The parameters obtained from the test consisted of firmness (maximum or peak force obtained as a result of compression) and cohesiveness (maximum negative force). All of the measurements were carried out at 25ºC and were replicated three times for each sample.

3.2.6 Statistical Analyses

Statistical analyses were conducted by using SPSS Statistics Desktop 22.0

(IBM Corporation, US). The results obtained were represented as the mean values of three individual replicates ± standard deviation (SD). Comparison of the mean was performed by one-way ANOVA using Tukey's test at 5% probability level.

40 3.3 Results and Discussion

3.3.1 Line Spread Test

In order to ensure compliance towards the IDDSI framework in terms of the ability to hold shape on a plate, LST was utilized fto develop the pureed rice porridge in this study. Since no standard has been developed for LST in the evaluation of pureed food for patients with dysphagia, the suitable concentration for each thickener was selected according to the characteristics of pureed food as listed in the IDDSI framework. As stated in the Table 2.2 (Section 2.2.1), the pureed rice porridge that suitable for patients with dysphagia should have smooth texture without any lump, not sticky, able to hold shape on a plate, and the liquid must not separated from the solid.

Figure 3.1 shows the LST measurements of different samples at all concentrations (1-3%) involved. The shorter distance spreads on the surface, the higher its consistency. As expected, the measurement values were decreased with higher consistency, due to increase concentration of thickener. By increasing the concentration of thickener, the starch or gum molecules begin to come into contact with one another, and thus the movement of molecules becomes restricted due to high viscosity (Saha & Bhattacharya, 2010).

The control sample (without the addition of thickener) was too runny and cannot hold shape on a plate (Figure 3.2a). This may cause choking risk for patients especially for those having difficulty in swallowing thin liquid. The pureed riice porridge with 1% starch (0.6 cm) showed less spreading than control sample (1.0 cm) but also cannot hold shape on a plate. However, the pureed rice porridge with the addition of 1% gum or 2% starch which showed less spreading values than

41 control sample were found to be suitable because they complied to the IDDSI framework (Figure 3.2b). For commercial product, there was no spreading (0 cm) and fulfilled to IDDSI framework based on the visual observation (Figure 3.2c).

On the other hand, pureed rice porridge samples with the addition of 2% gum and 3% starch or gum that showed no spreading (0 cm) were not selected because they were considered as very thick and sticky (Figure 3.2d).

One of the limitations of this test is that an increase in viscosity of thickened sample may cause LST to limit its ability in measuring the distance of spread. This statement also supported by a study conducted by Ettinger et al. (2014), who worked on pureed food and mentioned that the thick pureed product shows zero reading requires further instrumental analyses.

Gum 1%

Figure 3.1 LST measurements of pureed rice porridges formulated with different thickeners at different concentrations.

a b c d Gum 2%

Figure 3.2 Pureed rice porridge (a) without thickener (control sample); Gum 3% (b) with 1% gum and 2% starch; (c) commercial product; (d) with 3% starch, 2% and 3% gum.

42 3.3.2 Flow Behavior Test

To validate the results obtained from LST, the apparent viscosity (at the shear rate 50/s) of pureed rice porridge prepared with different thickeners were measured to determine the suitable concentration of each thickener by using commercial product as a reference. Based on the results tabulated in Figure 3.3, the addition of both types of thickeners (gum and starch-based) at 3% were shown to have higher apparent viscosity values compared to the reference sample. This result confirmed the findings from LST which indicates that 3% thickener in pureed rice porridge may be too thick for safe swallowing. Hence, the thickening of pureed rice porridge with 1% gum or

2% starch that produced samples with close apparent viscosity to the reference sample

(about 3 Pa∙s) were selected for further analyses. This apparent viscosity values (about

3 Pa∙s) have been found to be within the range (2.7-3.6 Pa∙s) as reported on previous study (Sharma et al., 2017) that worked on pureed carrot for people with dysphagia.

14.00 h

(Pa∙s) 12.00

10.00

8.00 g

6.00 f ef de d 4.00 c c c c c 2.00 b b a Apparent viscosity at at 50/s viscosity Apparent 0.00

1% 2% 3% Samples

Figure 3.3 Result of apparent viscosity at 50/s of pureed rice porridge samples containing different thickeners. The concentration of each thickener was selected based on the viscosity value similar to the commercial sample. Values with the same letter are not significantly different from each other at p < 0.05.

43 The stepped flow test data were then performed using mathematical models to study the rheological properties of pureed rice porridge after selection of suitable concentration for each thickener. The shear stress-shear rate data were well-fitted to the power law model with high determination coefficients (R2 above 0.98), and yield stress was calculated by using the Casson model, as shown in Table 3.2. All samples were non-Newtonian (showing shear-thinning behavior) over the shear rate range (0.1-

100/s) at 37ºC, since the n values were in the range of 0.16 to 0.34. The addition of each type of thickener caused not much difference in the n values, except for xanthan gum. The lower the n value, the greater the shear-thinning behavior. The shear- thinning behavior can be explained by continuous deformation due to breakage of hydrogen bonds between amylose molecules which resulting in the reduction of flow resistance and viscosity (Rohaya et al., 2013). Meanwhile, the greater shear-thinning behavior of rice porridge with the addition of xanthan gum was due to the ability of xanthan gum to form a complex aggregate with weak intermolecular forces in solution through hydrogen bonding and polymer entanglement (Figure 3.4), but at the same time these aggregates can be readily disrupted under shear (Sworn, 2000).

Table 3.2 Flow properties of pureed rice porridges prepared by different thickeners at selected concentration over a shear rate range from 0.1 to 100/s

Power Law Casson Yield Stress Samples n 2 n K (Pa∙s ) R 흈풐풄 (Pa) Control 0.27 ± 0.01bc 8.46 ± 0.17a 0.98 ± 0.01 6.03 ± 0.03a

Guar 1% 0.34 ± 0.01d 37.13 ± 0.77b 0.99 ± 0.01 25.37 ± 0.68b Xanthan 1% 0.16 ± 0.01a 78.55 ± 2.68d 0.98 ± 0.01 67.12 ± 2.38d Sago 2% 0.26 ± 0.00b 53.96 ± 1.18c 0.98 ± 0.01 39.48 ± 1.22c Tapioca 2% 0.29 ± 0.01bc 51.46 ± 1.39c 0.98 ± 0.01 37.23 ± 0.79c

Commercial 0.30 ± 0.02c 39.11 ± 2.47b 0.98 ± 0.02 26.72 ± 2.10b Note: Values were expressed as mean ± standard deviation of triplicate samples; values followed by the same letters in the same column were not significantly different at p < 0.05.

44

Figure 3.4 Schematic illustration of the ability of xanthan gum to form a complex aggregate in solution (Norton et al., 1984).

According to Funami (2011) and Yoon & Yoo (2016), K and yield stress obtained from the rheological models can be used to perceive ease of swallowing.

Zargaraan et al. (2013) also proposed that yield stress is another important property to be considered in the preparation of desirable food texture for dysphagia patients. Yield stress can be defined as the minimum stress that initiating the flow of a sample. The lower the yield stress, the easier the sample to be swallowed as less force required from the tongue to swallow (Yoon & Yoo, 2016). The pureed rice porridge with guar gum showed similar K and 휎표푐 values with the commercial product. The lower of K and 휎표푐 values achieved by guar gum sample compared to other thickened rice porridge was due to its flexible structure which inhibits the formation of intramolecular hydrogen bonding (Wielinga, 2000), making it easy to swallow. In contrast, the addition of xanthan gum resulted in the highest consistency and yield stress of pureed rice porridge was related to the interactions between gelatinized granules enhanced by xanthan gum

(Kim & Yoo, 2006), which can be difficult to swallow. Based on the results, the addition of sago and tapioca starch in pureed rice porridge showed similar K and

흈풐풄 values. However, both starch samples resulted in higher K and 흈풐풄 values compared to the guar gum sample and commercial product, which probably

45 caused by the strengthening of the amylose matrix structures (Russ et al., 2016).

It can be thus suggested that both starch samples are more difficult to swallow compared to the pureed rice porridge with guar gum and the commerical product.

3.3.3 Oscillatory Frequency Sweep Test

Table 3.3 presents the G’, G”, and tan 훿 of pureed rice porridge samples at

6.28 rad/s and 37°C. All samples exhibited weak gel-like properties, as shown by values of G’ which was higher than G”, as well as the tan 훿 values ranging from 0.19 to 0.51.

Table 3.3 Storage modulus (G’), loss modulus (G’’), and tan 훿 at 6.28 rad/s for different pureed rice porridge samples Samples G’ (Pa) G” (Pa) tan 휹 Control 70.12 ± 4.90a 17.14 ± 1.12a 0.24 ± 0.01a

Guar 1% 155.87 ± 6.25b 79.57 ± 0.43b 0.51 ± 0.02b Xanthan 1% 195.93 ± 3.88c 37.20 ± 0.64c 0.19 ± 0.00c Sago 2% 153.13 ± 10.44b 29.92 ± 1.00d 0.20 ± 0.01c Tapioca 2% 93.10 ± 3.38d 25.98 ± 0.22e 0.28 ± 0.01d

Commercial 67.10 ± 2.29a 27.15 ± 0.43e 0.40 ± 0.01e Note: Values were expressed as mean ± standard deviation of triplicate samples; values followed by the same letters in the same column were not significantly different at p < 0.05.

Tan 훿 provides information on viscoelastic properties of a sample, considering both solid-like and liquid-like behavior (tan 훿 = G”/G’) (Sharma et al., 2017).

Furthermore, tan 훿 can be one of the rheological parameters used to perceive the ease of swallowing. The lower the tan 훿, the higher the contribution of solid-like behavior of the sample, and the higher the energy required to break the intermolecular bonding

(Leite et al., 2012). It is apparent from the results that pureed rice porridge thickened with 1% xanthan gum (with lower tan 훿 and higher G’) had more solid-like behavior compared with other samples, hence more difficult to swallow. A large difference in

46 viscoelastic behavior of pureed rice porridge with xanthan gum compared to the commercial product can be related to the rigid rod-like structure of xanthan gum with extraordinary stability (Dogan et al., 2011)

Beside xanthan gum, it is noticeable that the guar gum samples showed the highest tan 훿 which means that the contribution of liquid-like behavior was higher after the addition of guar gum in pureed rice porridge. Such a tendency was in good agreement with the results of Yoo et al. (2005) and can be explained by the high substitution ratio of guar gum which allowing water to penetrate easily. Compared with xanthan gum, the pureed rice porridge thickened with guar gum had significantly lower G’ value with a more significant contribution of viscous properties, indicating less stiff structure for easy swallowing.

For starch, there is a positive relationship between the G’ and its amylose content. The higher the amylose content, the higher the G’. Sullivan et al. (2010) reported that more energy is needed to break down the linearity and extensive hydrogen bonding of amylose molecules. Since sago starch contains higher amylose content (27%) than tapioca starch (17%) (Wattanachant et al., 2002), the pureed rice porridge with sago starch showed significant higher G’ value than tapioca starch. The higher G’ and lower tan 휹 of sago starch sample imply that it is more difficult to swallow compared to tapioca starch. Compare with guar gum sample, pureed rice porridge with tapioca starch showed significantly lower tan 휹 and G’ value.

Therefore, besides guar gum sample, the lowest G’ value from purred rice porridge would also suggest a weaker structure and easier to be swallowed.

Therefore, the findings from this test would seem to indicate that the ease in swallowing for patients with dysphagia might depend on both the high tan 휹 as well as low G’ (low contribution of solid-like behavior) of the sample.

47 3.3.4 Textural Measurements

Many research suggested that foods that are soft and cohesive are more suitable and safer to swallow for people with dysphagia (Cichero, 2016; Tokifuji et al., 2013).

The soft texture is preferred because it can be processed more easily by a tongue-palate compression without teeth mastication (Aguilera and Park, 2016) and improved the miscibility of the food with saliva (Sharma et al., 2017). Cohesiveness defined as the degree to which sample hold together in a mass, is another parameter to determine the ease of swallowing since a “scattered” bolus may cause choking easily (Pascua et al.,

2013; Ishihara et al., 2011).

Figure 3.4 demonstrates the firmness and cohesiveness of pureed rice porridge samples obtained using back extrusion test. In general, all thickened samples showed higher firmness and cohesiveness values compared with the control sample. However, the results showed that the cohesiveness values were close to each other among all thickened samples, implying that the type of thickener had less effect on the cohesiveness of pureed rice porridge. Taking commercial product as the reference, the pureed rice porridge with guar gum showed no significant difference in firmness.

Meanwhile, the firmness of pureed rice porridge with guar gum was lower than pureed rice porridge with xanthan gum which can be described by its flexible conformational structure as compared with the rigid conformational structure of xanthan gum molecules. From the results, pureed rice porridge with sago starch also showed higher firmness compared to tapioca starch. This observation was consistent with the findings of G’ in this study (Section 3.3.3) which noted that higher amylose content of sago starch exhibited firmer structure of rice porridge and assumed to be more difficult to swallow as compared to tapioca starch sample.

48

1.2 E 1.0

0.8 D e C d 0.6 c b B b B 0.4

0.2 A a

0.0

Firmness, Cohesiveness Firmness, (N) Control Guar 1% Xanthan 1% Sago 2% Tapioca 2% Commercial Samples

Firmness Cohesiveness Figure 3.5 Textural properties (firmness and cohesiveness) of pureed rice porridges prepared by different thickeners. The letters (A-E) represented significant differences in firmness values; the letters (a-e) represented significant differences in cohesiveness values at p < 0.05.

49 3.4 Conclusion

The effects of type and concentration of thickener on the rheological and textural properties of pureed rice porridge were investigated. First, LST was utilized to develop the pureed rice porridge that complies with the IDDSI framework. Since the pureed rice porridge with the addition of either 1% gum or 2% starch were fulfilling to the IDDSI framework, it is expected that these samples are safe for patients with dysphagia. To validate the results of LST, the suitable concentration for each thickener was also determined by using the commercial product as a reference. The overall results showed that the thickening of pureed rice porridge with 1% gum or 2% starch produced samples with close apparent viscosity to the commercial product at the specific shear rate (50/s). These results confirmed the findings from LST and hence

LST can be considered to be a useful screening tool to evaluate the consistency of pureed food.

The results of the present study also revealed that the pureed rice porridge which had similar apparent viscosity with the commercial product at a specific shear rate gave differences in other rheological (n, K, and yield stress) and textural properties

(firmness and cohesiveness). Each thickener had its synergistic effect with pureed rice porridge and resulted in variation of ease of swallowing. The synergistic effect of guar gum with pureed rice porridge can be implied to be almost similar to the commercial product which evident through the results of K, 휎표푐, and firmness obtained in this study. The strong structure of pureed rice porridge with xanthan gum, evident through high yield stress, high G’, low tan δ, and high firmness indicates its difficulty in swallowing. The pureed rice porridge with tapioca starch which exhibited similar flow properties as sago starch had softer structure due to its lower G’ and firmness may also help to ease swallowing.

50 CHAPTER 4

CHARACTERIZATION OF INSTANT RICE PORRIDGE: PHYSICOCHEMICAL, RHEOLOGICAL, AND TEXTURAL ANALYSES

4.1 Introduction

In this modern lifestyle, people tend to be more demanding on foods that require fast preparation and convenience. Cooking rice porridge that suitable for patients with dysphagia can be a very time consuming and tedious process, where blending or straining to remove lumps are needed during preparation. In order to overcome this problem, efforts of developing instant rice porridge (powder form) were carried out in this study. This developed instant rice porridge that specially produced for patients with dysphagia is ready for reconstitution in a short time by using hot water, hence it is suitable for working families, hospitals, and nursing homes. In addition to easy and fast preparation, the drying of rice porridge also can help to extend the product’s shelf life.

As a continuation from Chapter 3, the drying process was applied to those selected freshly prepared rice porridge samples. The experiments were then divided into two main sections: (1) analyses on instant rice porridge and (2) analyses on reconstituted rice porridge. In the first section, the effect of different types of thickener on physicochemical and pasting properties of instant rice porridge was evaluated. In the second section, the rheological properties, textural properties, and the effect of salivary amylase on the reconstituted rice porridge were carried out in order to evaluate the ease of swallowing for patients with dysphagia.

51 4.2 Materials and Methods

4.2.1 Preparation of Instant Rice Porridge

The fresh pureed rice porridge samples with 1% gum (xanthan and guar) and

2% starch (tapioca and sago) were subjected to hot air drying in a cabinet dryer at 80ºC for 3 h. The control sample without any addition of thickener was also prepared for comparison. All the dried samples were then ground into powder form and passed through a 1 mm sieve before they were kept in air-tight containers and stored in a desiccator. The concentration for each thickener was selected based on the results provided in the previous chapter (Section 3.3.1 and 3.3.2).

4.2.2 Analyses on Instant Rice Porridge

4.2.2(a) Moisture Content and Water Activity

The moisture content of the powder sample was measured by the oven drying method following AOAC 925.10 (AOAC, 2000). The water activity (aw) was determined by using a digital aw meter (AquaLab Series 3, METER Group, Inc., USA) at 25 ºC. All the measurements were also performed in triplicates.

4.2.2(b) Swelling Power and Solubility

The method outlined by Sun & Yoo (2015) was used similarly to determine the swelling power and solubility of rice porridge powder in triplicate. The sample (0.5 g) was weighed into a beaker and mixed with 100 g distilled water. The dispersion was then moderately stirred for 1 h at room temperature, followed by heating at 95 ºC in a water bath for 30 min. The hot mixture was cooled to room temperature using an ice

52 water bath and centrifuged (Model 4000, Kubota Corporation, Japan) at 2100 × g for

20 min. The supernatant was collected in a pre-weighed aluminum dish. The swelling power was calculated using the weight of wet sediment in the centrifuge tube based on

Equation 4.1:

Weight of wet sediment (g) Swelling power (g/g) = (4.1) Weight of dry sample

The supernatant was then evaporated for 4 h in an oven at 120 ºC. The solubility was calculated using the following Equation 4.2:

Weight of dried supernatant (g) Solubility (%) = × 100% (4.2) Weight of dried sample (g)

4.2.2(c) Bulk Density (Tapped Density)

The tapped density was measured according to the method described by

Gbadamosi & Oladeji (2013) with minor modification. The rice porridge powder sample (2.5 g) was inserted into a 5 mL graduated cylinder. The cylinder was tapped continuously for 100 times and the density (g/mL) was calculated as weight of powder

(g) per powder volume (mL).

4.2.2(d) Pasting Properties

The pasting properties of rice porridge powder were measured using the Rapid

ViscoTM Analyzer (Model RVA Series 4, Newport Scientific Pvt. Ltd., Warriewood,

Australia) according to Marta & Tensiska (2017) with slight modification. The rice porridge powder (2.5 g, adjusted to 12% moisture basis) was weighed directly in the aluminum RVA sample canister, followed by the addition of distilled water to make the total constant sample weight of 27.5 g. A programmed heating and cooling cycle

53 were used respectively where the samples were held at 30ºC for 1 min, heated to 95ºC for 3.7 min, held at 95ºC for 2.5 min before cooling to 50ºC in 3.8 min, and then held at 50ºC for 2 min. The measurements were replicated three times for each sample. The parameters obtained from this analysis consisted of peak viscosity, breakdown viscosity, relative total setback, and pasting temperature. The relative total setback was calculated based on Arocas et al. (2009) using the following Equation 4.3:

Final viscosity − Trough viscosity (Pa ∙ s) Relative total setback = (4.3) Final viscosity (Pa ∙ s)

4.2.3 Analyses on Reconstituted Instant Rice Porridge

4.2.3(a) Line Spread Test

To select the most suitable ratio of rice porridge powder to hot water, a preliminary test was conducted for each sample with different thickener using LST

(Table 4.1). The final ratio for each rice porridge powder sample was selected based on its compliance with the characteristics of pureed form listed in IDDSI framework

(Table 2.2). The testing procedure of LST was conducted as previously described in

Section 3.2.3.

Table 4.1 List of the different volume of hot water used (mL) to obtain the optimal ratio for each sample (1 g)

Xanthan Guar Tapioca Sago Samples Control 1% 1% 2% 2% Amount of hot water (mL) 6, 7, 8 10, 12, 14 10, 12, 14 6, 7, 8 6, 7, 8

4.2.3(b) Rheological Measurements

This analysis was performed using the same methods as described earlier in

Section 3.2.4.

54 4.2.3(c) Textural Measurements

This analysis was performed using the same methods as described earlier in

Section 3.2.5.

4.2.3(d) Effect of Salivary Amylase

The effect of salivary amylase on the viscosity of reconstituted rice porridge was carried out based on the method described by Chung et al. (2012) with modification. The changes in viscosity were determined by using rheometer and followed the procedures of stepped flow test which described earlier in Section 3.2.4.

To study the effect of salivary amylase on the rice porridge, measurements were made on each sample by using artificial saliva either with α-amylase or without α-amylase.

The saliva to sample ratio of 1:4 was used (Sanz & Luyten, 2006). The formulation of artificial saliva (listed in Table 4.2) was adapted from Hur et al. (2009) and it was adjusted to pH 6.8 ± 0.2.

Table 4.2 Compositions of artificial saliva (Hur et al., 2009)

Componnets Concentration Volume Mass (g/L) (mL) (mg) Potassium chloride, KCl 89.6 10.0 Potassium thiocyanate, KSCN 20.0 10.0 Sodium phosphate, NaH2PO4 88.8 10.0 Sodium sulfate, NaSO4 57.0 10.0 Sodium chloride, NaCl 175.3 1.7 Sodium bicarbonate, NaHCO3 84.7 20.0 Urea 25.0 8.0 α-amylase type VI-B from porcine pancreas 290.0 (Sigma-Aldrich, A3176) Mucin from porcine stomach type II 25.0 (Sigma-Aldrich, M2378) Uric acid 15.0 Note: All chemicals and reagents used in this test were analytical grades.

55 4.2.4 Statistical Analyses

Statistical analysis was conducted using SPSS Statistics Desktop 22.0 (IBM

Corporation, US). The results obtained were represented as the mean values of three individual replicates ± standard deviation (SD). Comparison of the mean was performed by using one-way ANOVA using Tukey’s test at 5% probability level. The correlation between response variables was calculated using Pearson Correlation analysis.

4.3 Results and Discussion

4.3.1 Analyses on Instant Rice Porridge

4.3.1(a) Moisture Content and Water Activity

Table 4.3 presents the moisture content and aw of the rice porridge powder samples. Moisture content is a measurement of the total amount of water present in a sample. The results showed that the moisture content values increased with the presence of thickener in rice porridge powder. This is because thickener can act as a water-binding agent where it holds water and prevents the water loss during the cooking process (Alam et al., 2009). Nevertheless, the moisture content of all samples were in the range of 7.02-7.81%. The moisture content values obtained from this study were found almost similar with previous work carried out by Mandge et al. (2014) who reported 8% was the desired moisture content for their developed instant multigrain porridge.

56 Table 4.3 Moisture content and water activity of different rice porridge powders

Samples Moisture content (%) aw Control 7.02 ± 0.16a 0.31 ± 0.00b Xanthan 7.53 ± 0.05ab 0.27 ± 0.00a Guar 7.42 ± 0.34ab 0.25 ± 0.01a Sago 7.61 ± 0.16b 0.32 ± 0.00b Tapioca 7.81 ± 0.16b 0.36 ± 0.00c Note: Values were expressed as mean ± standard deviation of triplicate samples; values followed by the same letters in the same column were not significantly different at p < 0.05.

Water activity determines the ability of water in food to react with microorganisms. The higher the water activity, the higher the amount of free water in food, and hence the faster the microorganisms will be able to grow. All the aw values of rice porridge powder samples in this study varied from 0.25-0.36. These values also were in line with previous results obtained by Loypimai &

Moongngarm (2015) and Moussa et al. (2011) who worked on instant porridge.

Besides, the significantly lower aw values obtained by rice porridge powders with xanthan and guar gum indicated that gum has greater water holding capacity than starch, which can help to retain water during cooking or drying process.

According to Abdel-Haleem & Omran (2014), most of the microbial activity, fungi, and yeasts are inhibited when aw below 0.6, 0.7, and 0.8, respectively. In addition, Fernández-López et al. (2009) mentioned that the ideal range of aw for low moisture food should be between 0.11 to 0.40. Food with low aw is often desirable to the consumers due to the perception that microorganisms are unable to grow in dry condition, and thus the shelf life of food can be extended

(Ijabadeniyi & Pillay, 2017). However, according to Beuchat et al. (2013), many microorganisms such as Salmonella spp., Escherichia coli O157:H7, Listeria monocytogenes, Cronobacter sakazakii, Staphylococcus aureus, and Clostridium botulinum capable to survive in low aw foods. Finn et al. (2013) also added that presence of low numbers of food pathogens like Salmonella in food pose a risk

57 even though their growth are inhibited. Therefore, control measures such as appropriate preparation methods and proper storage condition should be implemented to limit the contamination and other unexpected risk.

4.3.1(b) Swelling Power and Solubility

Swelling power is the ability of the granules to increase in size with water absorption (Kaur et al., 2011). Solubility is the extent to which the components of the powder particles dissolve in water (Dhanalakshmi et al., 2011). Both of these parameters are the key to determine the reconstitution quality of the instant powder.

The swelling power and solubility values of the rice porridge powder samples were in the range of 9.94-17.58 g/g and 28.33-53.75% respectively, as summarized in Table

4.4. The results indicated that the swelling power of rice porridge was increased in the presence of thickener. This can be supported by Rojas et al. (1999) who reported that the presence of hydrocolloids (xanthan, alginate, and carrageenan) helped to promote the capacity of wheat starch granules to swell. However, Song et al. (2006) reported that the starch-hydrocolloid mixture exhibited lower swelling power than control sample because water could not penetrate starch phase due to the increase in viscosity of the continuous hydrocolloid phase.

Table 4.4 Swelling power and solubility of different rice porridge powders

Samples Swelling power (g/g) Solubility (%) Control 9.94 ± 0.34a 28.33 ± 1.00a Xanthan 17.58 ± 1.17c 48.05 ± 1.35b Guar 14.96 ± 0.81b 53.75 ± 2.41c Sago 11.36 ± 0.14a 30.12 ± 1.41a Tapioca 13.75 ± 0.54b 30.25 ± 0.63a Note: Values were expressed as mean ± standard deviation of triplicate samples; values followed by the same letters in the same column were not significantly different at p < 0.05.

58 Based on the results, the greatest swelling power of rice porridge powder with xanthan gum could be due to the ability of xanthan gum to form interactions among the gelatinized granules (Mandala & Bayas, 2004). The same authors also mentioned that the xanthan gum could entrap and keep the gelatinized starch granules closely, thus increasing the forces on these granules to facilitate water absorption and enhance the swelling process. Besides, the presence of guar gum in rice porridge powder showed the second highest value in swelling power. The possible explanation for the high swelling power of guar gum sample obtained in this study can be associated with the high branching degree of guar gum as well as its great hydration capacity (Yoo et al., 2005).

The swelling power of a powder sample also can be influenced by the size of starch granules. The presence of tapioca starch in rice porridge powder exhibited higher swelling power compared to the control sample. The observed higher swelling power could be interpreted as the result of the larger granule size of tapioca starch (4-

35 µm) which capable of holding more water than the rice starch (1-3 µm) (Sun &

Yoo, 2015). In relation to the smaller granule size of rice starch, the control sample had lowest swelling power due to strong associative force within the granular arrangement and hence required more energy to initiate the relaxation (Qazi et al.,

2014). Also, the difference in swelling properties among starches could be attributed to variation in amylose content. According to Lii et al. (1996), the higher the amylose content, the lower the extent of granular swelling. This is because amylose acts as an inhibitor of swelling in starch (Singh et al., 2003). This can be proven by the rice porridge with sago starch that showed lower swelling power in this study with the reason of sago starch has higher amylose content than tapioca starch.

59 For the solubility test, no significant difference in solubility values was observed between the control sample and sample with starch. This is probably because starch is generally considered to be insoluble in water (Li & Nie, 2016). With the presence of more starch, aggregation of starch components may occur where more hydrogen bonding of starch-water being replaced by hydrogen bonding between aligned chains of amylose, especially during heating and cooling conditions (Murphy,

2000). In contrast to its low swelling power, the high solubility of the control sample could be due to its small granule size. The small granule size of starch probably results in granule suspension and loss in supernatant during centrifugation (Lin et al., 2013).

The results also revealed that the rice porridge with gum showed higher solubility values than starch. This is because gum is usually considered as a water-soluble hydrocolloid. Taking rice porridge with guar gum as an example, its highest solubility was mainly because of the presence of high percentage of water-soluble polysaccharides (33-40% galactose units) in guar gum. Consequently, the galactose units also prevent strong cohesion of the main backbone and allow water to penetrate easily to hydrate or dissolve the gum (Wielinga, 2000).

4.3.1(c) Bulk Density (Tapped Density)

The bulk and tapped density are the indicators of the packing and arrangement of the particles (Mirhosseini & Amid, 2013). During drying and packing, the total volume of the inter-particle voids can change and thus tapped density is often measured instead of bulk value to obtain more reproducible result (Mirhosseini &

Amid, 2013). Tapped density is the measurement value results after a volume of powder has been tapped under specific condition. Based on the results recorded in

Figure 4.1, the tapped density of rice porridge powder samples were ranged from 0.86

60 to 0.93 g/mL. A lower bulk density values (0.57-0.70 g/mL) were obtained from the study conducted by Mayachiew et al. (2015) who worked on extruded instant rice porridge with bean. This indicates that the bulk density of a particulate food material could vary depending on the ingredients added and their interaction. According to

Roongruangsri & Bronlund (2016), bulk density can be affected by the type of drying and drying conditions (temperature, air velocity, and air humidity). The same authors also reported that higher bulk density was obtained in pumpkin powder prepared by hot air drying compared to freeze drying.

In this experiment, the control sample (without thickener) had the highest bulk density, which similar to the study conducted by Mayachiew et al. (2015). Besides, the presence of thickener reduced the bulk density of rice porridge powder, which means that the larger volume is required for the small quantity of sample in packaging.

Furthermore, the rice porridge powder with gum showed lower bulk density (0.71-0.81 g/mL) compared to starch (0.86-0.89 g/mL), which probably can be related to the highly negative correlation (r = -0.978) found between bulk density and swelling power in this study. The negative correlation means the higher the swelling power of the sample, the lower the bulk density. These results also can be supported by Marta

& Tensiska (2017) and Roongruangsri & Bronlund (2016) which reported a similar trend. During heating, the starch granules absorb water and swell which cause the volume fraction of granules to be increased and also bulk density to be decreased.

Taking control sample as an example, it was shown to have the least swelling power but the highest in bulk density values.

61 1.00 e d c b 0.80 a

0.60

0.40

0.20 Tapped density (g/mL) density Tapped

0.00 Control Xanthan Guar Sago Tapioca Samples

Figure 4.1 Tapped density of different rice porridge powders. Values with the same letter are not significantly different from each other at p < 0.05.

4.3.1(d) Pasting Properties

The pasting characteristics of rice porridge powder samples were depicted in

Table 4.5. Overall, the pasting properties of control sample were notably different from the samples with a thickener. The presence of thickener showed significantly increased in peak viscosity of rice porridge powder, where gum had a more pronounced effect compared to starch. According to Shi & Bemiller (2002), the increase in viscosity of the starch-hydrocolloid mixture was due to the interaction between hydrocolloid molecules and solubilized amylose and amylopectin molecules during starch gelatinization. For instance, the higher peak viscosity of guar gum sample could partly be attributed to its high branching degree that increases guar-amylose interactions

(Juszczak et al., 2004). Peak viscosity can be defined as the maximum viscosity of the swollen granule before rupture and often refers as the water binding capacity of the starch (or mixture) (Chantaro et al., 2013). Most of the authors relate the greater swelling power with higher peak viscosity (Fadzlina et al., 2005; Karim et al., 2008;

Weber et al., 2009). A positive correlation was found between swelling power and

62 peak viscosity of rice porridge powder in this study (r = 0.910). Therefore, the significantly higher peak viscosity achieved by the rice porridge with gum lends support to the statement above that the presence of gum increased the capacity of starch granules to swell. Besides swelling power, the amount of amylose in starch also can affect the viscosity. As reported by Zaidul et al. (2007), high amylose content had been associated with lower peak viscosity. This is because amylose molecules tend to bind to each other very strongly (Lai, 2001) and in turn, reduce the swelling process. In the case of sago starch with high amylose content, the sample showed lower peak viscosity compared to tapioca starch.

Breakdown is the tendency of a sample towards shear force during the holding period at 95ºC (Karim et al., 2008). Again, the presence of sago starch helped in reducing the breakdown of rice porridge. This can be explained by the presence of high amylose content in sago starch that strengthens forces within the granules and prevents breakdown. Nevertheless, the high breakdown of rice porridge with gum was connected to high swelling power. Weber et al. (2009) reported that high swelling indicates a low degree of binding forces within the swollen granules and hence have weak swollen granule structure. This suggests that these samples are less resistance to shear and have a higher tendency to loss viscosity upon heating and holding (Nadiha et al., 2010). Furthermore, the significantly high breakdown of gum samples can be related to the fact that the presence of hydrocolloid can increase the shear force applied on the granules and increase the number of granular components released into the continuous phase (Mandala & Bayas, 2004).

Total setback is generally identified as the degree of retrogradation of starch

(aggregations of gelatinized starch), especially amylose molecules during cooling. For correct comparison among the different rice porridge powders, relative total

63 setback was calculated instead of total setback. The rice porridge with starch

(sago and tapioca) showed no significant difference in relative total setback value compared to control sample. Their relative total setback values were also higher than rice porridge with gum. Since total setback is positively correlated with the texture of products (Chantaro et al., 2013), control and starch samples which showed higher tendency to retrograde might form firmer structure after cooling.

The lower relative total setback value of rice porridge with gum indicated that the presence of gum restricts the tendency of starch to retrograde. The xanthan gum sample which had the lowest relative total setback value of was also in good agreement with Arocas et al. (2009). Leite et al. (2012) explained such effect occurs due to competition between xanthan gum and amylose molecules to form the intermolecular bond, hence reducing the amount of amylose-amylose interactions which are responsible for starch retrogradation. Retrogradation is also linked to syneresis which is undesirable particularly in dysphagia-oriented foods because the greater the syneresis, the higher the risk of aspiration (Funami, 2011). As a consequence, the significant lowest relative total setback value attained by xanthan gum sample implies it is safer for patients with dysphagia due to its higher ability to resist water separation.

Pasting temperature is the temperature when starch starts to swell. The results clearly show that the presence of thickener decreased the pasting temperature of rice porridge powder. The highest pasting temperature of the control sample was consistent with the study conducted by Hussain (2015) who worked on native rice starch and linseed gum blends. The plausible explanation of this effect is the negative relationship found between pasting temperature and swelling power in this study (r = -0.895). The stronger interaction between rice starch granules which can be indicated by its least

64 swelling power and peak viscosity cause more energy required to break the intra- and intermolecular bonds, resulting in a rather high pasting temperature. However, the reduced pasting temperature of samples with gum could lead to higher starch-gum interactions due to water penetration and earlier pasting (Hussain, 2015). The instantaneous swelling effect is very favorable and plays an essential role in rice porridge powder that aims for fast preparation.

Table 4.5 Pasting properties of different rice porridge powders determined using Rapid ViscoTM Analyzer (RVA)

Viscosity (Pa·s) Relative Pasting temperature Samples Peak Breakdown total setback (°C) Control 0.43 ± 0.02a 0.05 ± 0.00a 0.50 ± 0.01c 94.82 ± 0.34c Xanthan 4.41 ± 0.17d 2.56 ± 0.07c 0.26 ± 0.01a 48.47 ± 0.14a Guar 4.43 ± 0.12d 2.97 ± 0.13d 0.38 ± 0.02b 48.40 ± 0.10a Sago 0.99 ± 0.03b 0.13 ± 0.00ab 0.48 ± 0.02c 87.12 ± 2.48b Tapioca 1.45 ± 0.06c 0.27 ± 0.02b 0.49 ± 0.03c 84.37 ± 1.24b Note: Values were expressed as mean ± standard deviation of triplicate samples; values followed by the same letters in the same column were not significantly different at p < 0.05.

4.3.2 Analyses on Reconstituted Instant Rice Porridge

4.3.2(a) Line Spread Test

The most suitable ratio of rice porridge powder to hot water for each sample was selected (Table 4.6) based on their compliance with the characteristics of pureed form listed in IDDSI framework. All these samples showed no spreading occurs. As reported earlier in Section 3.3.1, the properties of pureed food that suitable for patients with dysphagia should not be too thick, no water separation, and able to hold shape on a plate. In this study, an increased amount of water to higher than the selected ratio resulted in water separation and unable to hold shape, particularly for control and starch samples (Figure 4.2). These samples exhibited both liquid and solid phase when more water is added which may pose a choking risk for patients with swallowing

65 difficulty. At the relatively lower amount of water, the sample became too thick or sticky for swallowing, which can be referred to Figure 4.3.

Table 4.6 List of suitable ratio of rice porridge powder to hot water for each sample

Samples Ratio of rice porridge powder to hot water Control 1:6 Xanthan 1% 1:12 Guar 1% 1:12 Sago 2% 1:7 Tapioca 2% 1:7

a b

Figure 4.2 (a) Control sample with water separation (ratio 1:7); (b) Control sample without water separation (ratio 1:6).

a b

Figure 4.3 Reconstituted rice porridge with guar gum (a) Too thick for swallowing and sticky texture (ratio 1:10); (b) Not too thick and able to hold its shape (ratio 1:12).

66 4.3.2(b) Flow Behavior Test

Table 4.7 illustrates all the rice porridge samples with and without the presence of thickener were well fitted to the power law model with high determination coefficients (R2 above 0.90) and yield stress were calculated by using Casson model.

All the samples showed non-Newtonian shear-thinning behavior (as evidenced by the n less than 1) with yield stress. Such behavior also common in foods such as ketchup

(Koocheki et al., 2009), mayonnaise (Štern et al., 2007), yogurt (Yu et al., 2016), and potato puree (Alvarez et al., 2004).

Table 4.7 Flow properties of reconstituted rice porridge samples prepared by different thickeners at selected ratio over a shear rate range from 0.1 to 100/s

Power Law Casson Yield Stress Samples n 2 n K ( Pa∙s ) R 흈풐풄 (Pa) a b b Control 0.19 ± 0.00 102.76 ± 4.08 0.90 ± 0.03 91.41 ± 3.88 b a a Xanthan 0.26 ± 0.01 74.85 ± 9.83 0.99 ± 0.01 59.03 ± 9.28 bc c c Guar 0.28 ± 0.00 139.45 ± 6.92 0.99 ± 0.01 110.35 ± 5.28 c b a Sago 0.34 ± 0.01 102.78 ± 5.10 0.98 ± 0.01 62.42 ± 3.38 bc d c Tapioca 0.33 ± 0.05 152.38 ± 12.65 0.99 ± 0.01 111.54 ± 7.54 Note: Values were expressed as mean ± standard deviation of triplicate samples; values followed by the same letters in the same column were not significantly different at p < 0.05.

Compared with the control (n = 0.19), the rice porridge with thickener showed significantly higher value of n in the range of 0.26-0.34. This finding indicated the control sample had most response towards shear. Consequently, it highlights the importance of thickener to reduce the rate of disruption upon shear in the reconstituted rice porridge. Based on the results, the n values of rice porridge with gum were also lower as compared to starch. As discussed in earlier chapter (Section 3.3.2), the rice porridge with xanthan gum showed greater shear-thinning behavior, due to the ability of xanthan gum to form a complex aggregate with weak intermolecular forces in solution. For rice porridge with guar gum, its high degree of shear-thinning characteristic can be explained by the unique guar gum structure. The structure of guar

67 gum consisted of a mannan main chain with alternate galactose branches inhibits the formation of intramolecular hydrogen bonding. This keeps the molecule in an extended form and allows it to interact with amylose molecules through intermolecular bonding readily, hence makes it higher tendency to loss viscosity with increasing shear rate

(Yoo et al., 2005). Besides, the n value of thickened food is crucial because it correlated to the sensory properties of the food. Marcotte et al. (2001) noted that low value is required if high viscosity and good mouthfeel (less slimy) characteristics are desired in food.

The most remarkable result to emerge from this flow behavior test data is that all the samples showed increment in term of K and 휎표푐 values after drying and reconstitution process, except for rice porridge with xanthan gum. This is because xanthan gum is considered as a thermoreversible gel where its structure can return to the original state upon cooling (Sworn, 2000). The same author also pointed out that the consistency of xanthan gum can recover almost instantaneously upon the removal of shear even though it is highly shear-thinning. The lowest K and 휎표푐 of rice porridge with xanthan gum suggest a less stiff structure which can be easier to swallow. On the other hand, the presence of tapioca starch in rice porridge contributed to highest in K and 휎표푐, which can be expected to cause difficulty in swallowing. Those high values obtained by tapioca starch sample may due to its high swelling power. In the case of guar gum sample, its presence showed greater effects on the increase of K and 휎표푐 compared to xanthan gum sample. It is probable that depolymerization of guar gum molecules occur during heating and shearing conditions where more galactose units removed from the main chain of mannose units and in turn cause the number of mannose units to be increased in the sample, hence allows the formation of intramolecular bonding between gum to be increased (Rao et al., 1981; Bradley

68 et al., 1989). Moreover, it is apparent from the results that both the control sample and rice porridge with sago starch attained similar K, yet the latter one had lower 휎표푐 value.

This can lead to the assumption that sago starch sample will be easier to swallow compared to the control sample.

4.3.2(c) Oscillatory Frequency Sweep Test

As was mentioned in Results and Discussion (Section 3.3.3), tan 훿 was the main parameter in this test because it can be used to perceive ease of swallowing by considering both solid-like (G’) and liquid-like behavior (G”). The lower the tan 훿, the higher the contribution of solid-like behavior. According to Ishihara et al. (2011), the strong solid-like structure can limit the miscibility of food with saliva and make it difficult to swallow.

The tan 훿 of different rice porridge samples at 6.28 rad/s and 37°C were represented in Figure 4.4. Overall, all the samples were characterized as weak gel and indicated solid-like behavior predominantly. Since the tan 훿 values were in the range of 0.1 - 1.0, all the samples were considered as safe-swallow food meant for dysphagia

(Ishihara et al., 2011). It is also interesting to note that all samples showed not significantly different in tan 훿, except for rice porridge with guar gum. Given the flexible conformation of guar gum, it was expected that the highest tan 훿 was related to its higher branching ratio and greater hydration capacity that allows water to penetrate easily between molecules (Li & Yeh, 2001). Therefore, it had the least stiff structure with lowest G’ compared to other samples, which make it easy to swallow.

69 0.40 b 0.35 0.30 0.25

δ 0.20 a tan 0.15 a a a 0.10 0.05 0.00 Control Xanthan Guar Sago Tapioca Samples

Figure 4.4 Tan 훿 at 6.28 rad/s for different reconstituted rice porridge samples. Values with the same letter are not significantly different from each other at p < 0.05.

Based on Figure 4.5, rice porridge with xanthan gum exhibited higher G’ compared to guar gum. There is evidence to support the finding that xanthan gum could act as a protective agent against starch granular integrity loss by surrounding the starch granules and forming a network around them when a force was applied

(Mandala et al., 2002). As a consequence, more energy is required to break the strong inter-particle bonding between starch and xanthan gum (Leite et al., 2012). In addition,

Dogan et al. (2011) and Mandala & Bayas (2004) reported that xanthan gum could strengthen the structure of starch because of its trisaccharide side chain able to align closely with the backbone, making the xanthan gum a stable and rigid rod.

3000 d 2500

2000 c c 1500 G' b 1000 a 500

0 Control Xanthan Guar Sago Tapioca Samples Figure 4.5 Storage modulus (G’) at 6.28 rad/s for different reconstituted rice porridge samples. Values with the same letter are not significantly different from each other at p < 0.05.

70 Furthermore, the results obtained from this analysis demonstrated that G’ was negatively correlated with swelling power (r = -0.800). The negative correlation means the lower the swelling power, the higher the G’ value. This is in line with previous findings of Lii et al. (1996) who reported that the rigidity of the granular starch structure was inversely proportional to the degree of granular swelling. This correlation is likely because low swelling power indicates a high degree of bonding within the swollen granules and hence a strong swollen granules structures

(Weber et al., 2009). Taking control sample as an example, its higher G’ compared to rice porridge with tapioca and sago starch could be attributed to its low swelling power and strong intra-granular bonds.

4.3.2(d) Textural Measurements

Textural properties of different rice porridge samples were shown in Figure

4.6. The firmness and cohesiveness of the reconstituted rice porridge samples were in the range of 1.11-2.08 N and 1.05-2.43 N respectively. The rice porridge with gum showed significantly lower in firmness and cohesiveness. These results were consistent with the previous finding of Kaur et al. (2015) who investigated the effects of different starch-gum combinations on the textural properties of noodle. In addition, the results also confirmed the earlier findings of this study where the soft texture was characterized by low G’ and high swelling power. This can be proven by the positive relationship found between firmness and G’ (r = 0.800) whereas the negative relationship between firmness and swelling power (r = -0.700) in this study. Moreover, the firmness also was highly negatively correlated with solubility (r = -0.930) and further support the study of Seetapan et al. (2015) who mentioned that more soluble and leachable polymeric molecules from starch granule resulting in a weaker structure.

71 Compared to rice porridge with gum, the control and both starch samples showed firmer structure could be contributed partly by their significantly higher relative total setback values (greater tendency to retrograde [Section 4.3.1(d)]. According to Wang et al. (2015), retrogradation process determines the initial hardness of starch- based food. The higher the total setback value, the greater the tendency for starch retrogradation, hence the firmer the structure of the sample.

3.0 D 2.5 d c C C 2.0 b B 1.5 a A a 1.0

0.5

0.0 Firmness, Cohesiveness Firmness, (N) Control Xanthan Guar Sago Tapioca Samples

Firmness (N) Cohesiveness (N)

Figure 4.6 Textural properties (firmness and cohesiveness) of different reconstituted rice porridge samples. The letters (A-E) represented significant differences in firmness values; the letters (a-e) represented significant differences in cohesiveness values at p < 0.05.

Cohesiveness measures the internal binding force which holds the food sample as a bolus during swallowing (Funami et al., 2012). The rice porridge with xanthan gum was lowest in the internal binding force, may be attributed to the formation of complex aggregates with weak intermolecular forces by xanthan gum in solution. Kaur et al. (2005) and Wang et al. (2015) reported that the less amylose leaching due to the complex formation might reduce its availability to form intermolecular hydrogen bonding which in turn caused decreased in the cohesiveness of the structure. Since guar gum molecules had higher solubility and able to form interaction with simple

72 structure of amylose chain, guar gum samples showed significantly higher cohesiveness compared to xanthan gum. Compared to control and sago starch sample, the presence of tapioca starch showed higher cohesiveness in rice porridge. This observed higher value could be interpreted by the high swelling power and solubility of tapioca starch sample. The leached molecules from tapioca starch can bind to the swollen restricted rice starch granule and hence enhance the cohesive energy (Seetapan et al., 2015).

4.3.2(e) Effect of Salivary Amylase

The main digestive enzyme in saliva is α-amylase. Enzyme of α-amylase is considered as an endohydrolase enzyme that responsible for the hydrolysis of starch by randomly cleaving α-1,4 glycosidic bonds in amylose and amylopectin to produce smaller molecules (Bornhorst et al., 2014). The mechanical structure of starch-based food could be broken down when in contact with human saliva and caused the viscosity of the food to be decreased. As was stated in Section 2.1.3, low viscosity can increase the risk of choking among patients with dysphagia.

Table 4.8 clearly shows the salivary amylase reduced the viscosity of all rice porridge samples. As expected, the control sample and rice porridge with starch showed higher changes in viscosity (94-97%) when in contact with salivary amylase.

This is in good agreement with Hanson et al. (2012) who reported that the saliva reduced the viscosity of starch-thickened water nearly 100%. Chen (2014) also mentioned that the interaction between amylase enzyme and starch ingredients is instantaneous and its effects on food consistency are also immediately obvious.

73 Table 4.8 Changes in apparent viscosities at 50/s of different reconstituted rice porridge samples before and after addition of salivary amylase

Viscosity at 50/s (Pa·s) Samples Changes in Viscosity (%) Without Amylase With Amylase c Control 2.78 ± 0.12 0.14 ± 0.03 95.12 ± 0.91 b Xanthan 3.01 ± 0.17 1.10 ± 0.02 62.07 ± 2.55 a Guar 4.48 ± 0.03 2.16 ± 0.03 52.05 ± 0.97 c Sago 3.57 ± 0.14 0.07 ± 0.00 97.93 ± 0.22 c Tapioca 4.35 ± 0.09 0.09 ± 0.01 97.95 ± 0.11 Note: Values were expressed as mean ± standard deviation of triplicate samples; values followed by the same letters in the same column were not significantly different at p < 0.05.

The effect of salivary amylase on the rice porridge with gum was less pronounced as compared to starch, which can be hypothesized to be safer in swallowing for patients with dysphagia. This finding appears to be well supported by Vallons et al. (2015) who proposed that the thickener which less susceptible to salivary amylase can help to improve the safety of swallowing among patients with dysphagia. The gum samples was less sensitive to the action of salivary amylase was mainly due to the absence of the particular α-1,4 glycosidic bond in the gum structure. For instance, xanthan gum molecules composed of α-1,3 bonds, β-1,2 bonds, and β-1,4 bonds which are not susceptible to salivary amylase. In addition to the bonds, there are other factors that lead to the inhibitory effect of gum on amylase activity. Brennan et al. (1996) and Sworn (2000) stated that xanthan and guar gum could act as a physical barrier to α-amylase-starch interaction by forming a layer around the starch granules, protecting them from enzyme attack. This also can be supported by Slaughter et al. (2002) who have addressed that the presence of gum may limit the water availability required for the break down of glycosidic bonds in starch.

Besides, Slaughter et al. (2002) reported that guar gum is a non-competitive inhibitor

74 of α-amylase where it binds directly to α-amylase and causes guar-amylase complex inactive.

75 4.4 Conclusion

The comparison of behaviors for different thickeners in instant rice porridge under physicochemical, pasting, instrumental (rheological and textural), and salivary amylase analyses were carried out in this chapter. The suitable volume of hot water to reconstitute each rice porridge powder sample also was successfully determined by

LST. In conclusion, rice porridge powder with gum exhibited distinct and more desired properties compared to starch under certain testing conditions. This chapter also significantly showed the potential of xanthan gum to be used as a thickener in instant rice porridge which can be proved by its high swelling power, high solubility, low pasting temperature, low n value, low K, low yield stress, and low firmness. All of these properties are able to contribute to good reconstitution quality of instant powder and the ease swallowing for patients with dysphagia. For rice porridge powder with sago starch, it showed the most similar to the control sample (without thickener) in several aspects, namely swelling power, solubility, K, tan 훿, cohesiveness, and effect of salivary amylase. Besides, the statistical analysis (correlation) also highlighted the importance of swelling power in the preparation of instant rice porridge for patients with dysphagia. Swelling power was found to have positive correlation with peak viscosity (r = 0.910) and negative correlation with bulk density (r = -0.978), pasting temperature (r = -0.895), firmness (r = -0.700), and G’ (r = -0.800).

76 CHAPTER 5

SENSORY EVALUATION OF INSTANT RICE PORRIDGE AMONG PATIENTS WITH DYSPHAGIA

5.1 Introduction

This chapter primarily focuses on the effect of thickener types on the sensory acceptability of the developed instant rice porridge among patients with dysphagia in

Hospital USM, Kelantan. The correlation analysis between instrumental and sensory parameters also was carried out to give better insight into the characteristics of the developed instant rice porridge samples.

5.2 Materials and Methods

5.2.1 Participants

Twenty participants (12 males and 8 females, 27-72 years, mean age 52.5 years, SD 13.8) were recruited from Hospital USM, Kelantan. The participants were individuals who were diagnosed with oropharyngeal dysphagia based on their medical record or clinical dysphagia examination that was carried out by an experienced speech-language therapist. No subject reported any problems with their five main senses (touch, taste, sight, hearing, and smell) and they were allowed to consume pureed food. Before the start of the sensory test session, each participant was informed of the procedures and written consent was obtained before the evaluation. Ethical approval was obtained from the Human Research Ethics Committee of USM (Protocol

Code: USM/JEPeM/17080367, Refer to Appendix B).

77 5.2.2 Samples and Preparation

Five samples were evaluated by each participant which include instant rice porridge (i) without any presence of thickener (control), (ii) with presence of xanthan gum, (iii) with presence of guar gum, (iv) with presence of sago starch, and (v) with presence of tapioca starch. All samples were prepared using hot water (refer Table 4.6 for the finalized ratio of rice porridge powder to hot water for each sample) and served at room temperature to participants.

5.2.3 Procedures

The sensory test was carried out in a closed room and supervised by a speech- language pathologist to monitor choking. Visual Analog Scale (VAS) was used to rate several sensory attributes, namely thickness, stickiness, swallowing effort, graininess, and overall acceptability (Table 5.1, Refer to Appendix C). All participants were required to rate the attributes on the 100 mm lines with descriptors labeled at both ends. The samples (about two teaspoons each) were placed in plastic cups (coded with random three-digit numbers) and presented to the participant one after another. The presentation order of the samples was randomized to minimize the effect of the order on responses. All participants were also reminded to rinse their mouth with provided water for cleansing purposes before testing each sample. Participants were allowed to have short rest periods in between if they feel fatigued during testing. The participants did not need to finish up the whole sample, only as much as they needed to make their evaluation. The testing process for each participant took about 30 minutes. Monetary incentive was given to the participants after the sensory test as a token of appreciation.

78 Table 5.1 Definitions for sensory attributes of the instant rice porridge samples (Janssen et al., 2007; Jiménez et al., 2013)

Sensory attribute Definition Thickness The viscous consistency of the food in mouth after the food is compressed via up-and-down motions of the tongue against the palate Stickiness The feeling of a sticky sensation by the tongue, palate, and throat, making it difficult to swallow Swallowing effort The effort required to transfer the food to the back of the palate and swallow Graininess The degree to which the food contains granules that can be perceived in the mouth

5.2.4 Statistical Analyses

The VAS score was determined by measuring the distance on the line between the left-hand end to the point which the participant marked. The sample mean values for each sensory attributes and instrumental measurements (rheology and texture) were calculated by using Excel (Microsoft Office, 2016). The Pearson’s Correlation (p <

0.05) was performed on sensory attributes and Principal Component Analysis (PCA) was performed on sensory attributes and instrumental measurements (XLSTAT software version 2018.1).

5.3 Results and Discussion

5.3.1 Correlation between Sensory Attributes

The effect of different thickeners on the sensory characteristics and acceptability of instant rice porridge were evaluated by patients with dysphagia. The average scores for the attributes for each sample were shown in Figure 5.1.

The instant rice porridge with xanthan gum had the lowest score in thickness, stickiness, swallowing effort, and graininess but highest in overall acceptability rating.

This result was consistent with Vickers et al. (2015) who reported that the fluid

79 thickened with xanthan gum was lower on the thickness and adhesive-related attributes. Based on Table 5.2, the overall acceptability of instant rice porridge showed negative correlation with all other attributes, where stickiness recorded the highest value (r = -0.891). Except for xanthan gum, the presence of guar gum and both starches increased the stickiness of instant rice porridge. Due to the significant high positive relationship found between stickiness and swallowing effort (r = 0.948) in this study, the results point to the probability that the less sticky texture of instant rice porridge was more acceptable by participants mainly because it is easier to swallow. This can be further strengthened by Ishihara et al. (2011) who proposed that swallowing effort is one of the important attributes associated with personal palatability.

Thickness 7.0 6.0 5.0 4.0 Overall 3.0 Stickiness acceptability 2.0 1.0 0.0

Swallowing Graininess effort

Control Xanthan Guar Sago Tapioca

Figure 5.1 Mean scores of sensory attributes of the instant rice porridge samples with different thickeners among patients with dysphagia (n = 20).

80 Table 5.2 Pearson’s Correlation coefficients of the five sensory attributes of the developed instant rice porridge samples

Swallowing Overall Variables Thickness Stickiness Graininess effort acceptability Thickness 1 Stickiness 0.229 1 Swallowing 0.354 0.948 1 effort Graininess 0.587 0.377 0.624 1 Overall -0.504 -0.891 -0.819 -0.248 1 acceptability Note: Values in bold were different from 0 with a significance level α = 0.05.

Apart from stickiness, the ease in swallowing can be achieved by manipulating the graininess of the instant rice porridge. The high grainy texture of rice porridge caused difficulty in swallowing among patients with dysphagia. According to Rofes et al. (2014), grainy foods that cause residues in the mouth (or throat) not only can lead to choking during swallowing but also can put the patients at risk for respiratory complications. The presence of starch and gum helped in reducing graininess of instant rice porridge, where the latter was more pronounced. As reported by many previous findings in the literature, starch-based thickener imparted a grainy texture while gum- based thickener has more therapeutic advantages because it was found to reduce granularity and thus improve the safety of swallow (Alvarez et al., 2008; Rofes et al.,

2014; Vilardell et al., 2016). Sharma et al. (2017) also reported that xanthan gum can help to reduce granularity which is similar to pureed carrot perceived as being very smooth.

Graininess was found to have a contribution to the sensory perceived thickness of instant rice porridge (r = 0.587) in this study. For instance, control sample was perceived to have the highest value of graininess as well as highest value of thickness.

This positive relationship also was in accordance with Matta et al. (2006) who reported that beverage prepared with starch-based thickener imparted grainy texture as well as

81 higher perceived thickness compared to gum-based thickener. Besides, the thickness was negatively correlated with overall acceptability (r = -0.504), indicating that the increase in thickness can decrease the overall acceptability of instant rice porridge among patients with dysphagia. Similar results were reported by Zargaraan et al.

(2015) who found that too high viscosity can lead to food refusal by patients with dysphagia. Dewar & Joyce (2006) also stressed that too high in viscosity may aggravate swallowing and give rise to malnutrition and dehydration among patients with dysphagia. Therefore, the observed lower overall acceptability in instant rice porridge with sago starch than tapioca starch could be attributed to its thickness.

5.3.2 Correlation between Sensory Attributes and Instrumental Measurements

Principal Component Analysis (PCA) is one of the multivariate analytical statistical techniques that is able to reduce the set of dependent variables to a smaller set of underlying variables (known as factors) based on the correlation among the original variables (Harry T. Lawless & Heymann, 1998). In this section, PCA was used to help us to better understand the behaviors of thickener in instant rice porridge by profiling the similarities or differences among analyzed samples based on the correlation between sensory attributes and instrumental measurements.

Based on Figure 5.2, the first two principal components (PC) were extracted explaining 74.16% of the total variance (45.709% for PC1 and 28.37% for PC2). The parameters that are close to each other are positively correlated; parameters that are separated by 180º are negatively correlated; and parameters that are separated by 90º are independent (Cañeque et al., 2004). Taking the first quadrant of the biplot as an example, graininess was located near to G’, G”, firmness, thickness, and cohesiveness, indicating that they were positively correlated with each other which can be proven

82 through their correlation coefficients obtained in Table 5.3. The control sample was located in the first quadrant and representing the grainy, firm, thick, and cohesive texture. The high firmness, thickness, and cohesiveness imparted by control sample can be related to its high solid-like behavior (G’) that required more energy to break the intermolecular bonding, and hence more difficult to swallow. As mentioned above

(Section 5.3.1), the high grainy texture of the control sample also was not suitable for patients with swallowing difficulty because it may increase the risk of choking.

The instant rice porridge with the presence of tapioca and sago starch were located on the second quadrant. On the second quadrant, there were two sensory attributes (swallowing effort and stickiness) and three rheological measures of n

(shear-thinning behavior), K (consistency), and yield stress. All of these parameters were positively correlated. The high positive correlation between stickiness and n (r =

0.724) in this study also can be supported by Vickers et al. (2015) who reported the similar result in thickened drinks. However, all the parameters on this quadrant were negatively correlated to overall acceptability that was located on the opposite quadrant.

These results would seem to imply that the instant rice porridge with both starches which showed lower score in overall acceptability were due to their higher values for rheological measures, stickiness, and swallowing effort.

Another remarkable result to emerge from the second quadrant is the positive correlation between swallowing effort and n (r = 0.619). The positive correlation obtained in this study was in line with O’Leary et al. (2010) who proposed that thickened liquids with greater shear-thinning (low n value) provide safer swallowing among patients with dysphagia. This is because the high apparent viscosity at low shear rates prior to swallowing can prevent the fluid to rapidly entering the airway, and the shear-thinning may make the fluid easy to swallow due to less muscular force

83 needed. In contradiction with the earlier finding of Nishinari et al. (2011), they reported that the solution with high viscosity at low shear rate caused more difficulty in swallowing as the bolus may split into small pieces and stay longer in the oral cavity.

Besides n value, the findings from this study underlined that the low K of instant rice porridge with low yield stress helped to increase the ease of swallowing.

This lends support to the study conducted by Sharma et al. (2017) who worked on pureed carrots. In their research, they also mentioned that the increase in ease of swallowing was resulted from the easy mixing of saliva with food and thus giving the perception of smoothness. Furthermore, Zargaraan et al. (2015) highlighted that the increase of the ease of swallow due to the increase of K is true for liquid but not necessarily for foods in semi-solid form.

In the present study, the apparent lack of correlation between sensory perceived thickness and instrumental measure of K (r = 0.167) indicated that the differences in consistency among samples were less likely to be distinguished by the participants in sensory evaluation. This may be consistent with Nyström et al. (2015) who stated that the patients with dysphagia were only able to evaluate the ease of swallowing for the respective model fluids and less able to assess other attributes that are related to the mouthfeel.

On the left side of the biplot, the presence of gum was shown to have more desirable characteristics in instant rice porridge. The presence of guar gum has been shown to aid in modifying the texture of instant rice porridge by reducing its graininess, thickness, firmness, and cohesiveness. It is also interesting to note that the instant rice porridge with xanthan gum exhibited properties unlike instant rice porridge with sago and tapioca starch. The instant rice porridge with xanthan gum was less

84 sticky, low n, low K, low yield stress, and easy to swallow. Therefore, it was the most acceptable sample among patients with dysphagia.

Figure 5.2 Principal component plot showing relationships between sensory attributes and instrumental measurements (rheology and texture) for instant rice porridge samples developed by different thickeners.

85 Table 5.3 Pearson’s Correlation analysis on sensory attributes and instrumental measurements (rheology and texture) of the developed instant rice porridge

Variables n K Yield stress G' G" tan d Firmness Cohesiveness Thickness -0.454 0.167 0.300 0.494 0.938 0.220 0.330 0.325 Stickiness 0.724 0.755 0.442 0.028 0.071 0.139 0.492 0.675 Swallowing effort 0.619 0.594 0.288 0.323 0.267 -0.111 0.675 0.792 Graininess -0.092 0.165 0.125 0.933 0.749 -0.573 0.927 0.849 Overall acceptability -0.488 -0.661 -0.440 0.091 -0.251 -0.463 -0.227 -0.419 Note: Values in bold were different from 0 with a significance level α = 0.

86 5.4 Conclusion

In summary, the sensory evaluation of five different instant rice porridge samples was successfully conducted among patients with dysphagia. Patients can accept all of the samples and no choking happened during sensory testing. The goal to evaluate the characteristics of instant rice porridge that is suitable and acceptable for patients with dysphagia was achieved by using PCA together with Pearson’s correlation analysis. The combination of sensory evaluation and instrumental measurements (rheology and texture) are also beneficial to reveal more information regarding the influence of each thickener in developed instant rice porridge. The control sample imparted a firm structure with grainy texture. The instant rice porridge with sago and tapioca starch which exhibited sticky texture, high yield stress, high consistency, and low shear-thinning behavior were hard to swallow. The instant rice porridge with xanthan gum exhibited characteristics opposite to instant rice porridge with both starches and was most desirable for patients with dysphagia.

To sum up, the overall acceptability of a food product is usually affected by various factors which cannot be described by a single attribute. The findings from this study highlight the importance of swallowing effort, stickiness, and rheological parameters in determining the overall acceptability of instant rice porridge that is suitable for patients with dysphagia.

87 CHAPTER 6

CONCLUSION AND RECOMMENDATIONS

6.1 Conclusion

The work in this study presented findings that could help to understand the suitability of different starch and gum as thickener using pureed rice porridge as the food model for patients with dysphagia. The suitable concentration for each thickener was determined using commercial dysphagia-oriented porridge product as the reference in Chapter 3. The overall results found that different instrumental measures

(rheology and texture) which contributed differently in predicting the ease of swallowing are important in the development of texture-modified food for patients with dysphagia.

This was further stressed that it is insufficient to only focus on viscosity measurement at specific shear rate because the pureed rice porridge which had similar apparent viscosity with commercial product showed differences in other rheological and textural properties.

The instant rice porridge that was ready for reconstitution in a short time using hot water was developed in Chapter 4. The correlation analysis between instrumental measurements and sensory evaluation also were carried out in Chapter 5 to give better insight on the behavior of thickeners in instant rice porridge while producing the right texture of food. The findings of this study indicate that xanthan gum has the potential to be used as a thickener in instant rice porridge.

In conclusion, this study has successfully developed instant rice porridge that is suitable for consumption and was sensorily accepted by selected patients with dysphagia. This could indicate the possibility of introducing instant rice porridge as another food choice for patients with dysphagia, with cheaper cost to reduce their financial burden.

88 6.2 Recommendations

The developed instant rice porridge with the presence of xanthan gum has the advantages of high swelling power and solubility as well as low pasting temperature that make it ready for reconstitution in a short time using hot water. Due to such reason, application of this developed instant rice porridge appears to be promising in nursing homes and hospitals which require fast preparation and convenience. However, the nutritional quality of this developed instant rice porridge should be further studied and discovered towards the opportunity of developing a new enriched pureed food for patients with dysphagia. Development of food with complete nutritional value will help to overcome the malnutrition problem among patients with dysphagia, albeit if taken in small quantity.

The lack of standardizing guidelines and objective measurements have contributed further to affect the safety, reliability, and quality of texture-modified food.

Therefore, it is necessary to develop the quantitative standard which provides us the acceptable ranges of consistency and texture for pureed food. Further swallowing studies and involvement of larger sample size in sensory evaluation test also need to be carried out to help in delivering better treatment outcomes among patients who have dysphagia.

This present study has some limitations and weaknesses. Despite this, the author believes this research has revealed that a few parameters which can affect the ease of swallowing and overall acceptability of pureed food. The knowledge from this research could serve as the basis for future studies and development of texture- modified food in pureed form.

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107 APPENDICES

Appendix A Commercial dysphagia-oriented rice porridge that used as a reference

Appendix B Ethical approval letter from the Human Research Ethics Committee of USM

Participant Number: ______Date: ______

Sample code: ______

1. Thickness

Extremely Not at all

2. Stickiness

Not at all Extremely

3. Swallowing effort

Least difficult Most difficult

4. Graininess

Not at all Extremely

5. Overall pleasantness

Extremely Extremely unpleasant pleasant

Comments/ Suggestions:

Appendix C Example of sensory evaluation form

LIST OF PUBLICATIONS

Syahariza, Z. A., & Yong, H. Y. (2017). Evaluation of rheological and textural properties of texture- modified rice porridge using tapioca and sago starch as thickener. Journal of Food Measurement and Characterization, 11(4), 1586–1591.

Yong, H. Y., Syahariza, Z. A., Uthumporn, U., & Karim, A. A. (2017). Rheological and textural properties of texture-modified rice porridge: Comparison between starch and gum as thickener. In International Conference on Food Science and Nutrition 2017 (pp. 20–25).