Effect of Hydrocolloid Type on Rheological and Sensory Properties of Pureed Carrots

Home , Food rheology

Effect of hydrocolloid type on rheological and sensory properties of pureed carrots

Madhu Sharma

A Thesis

Presented to

The University of Guelph

In partial fulfilment of requirements for the degree of

Master of Science

Food Science

Guelph, Ontario, Canada

ABSTRACT

Effect of hydrocolloid type on rheological and sensory properties of pureed carrots

Madhu Sharma Advisor:

University of Guelph, 2015 Dr. Lisa Duizer

Hydrocolloids are added to pureed foods to give desired consistency based on visual judgement, due to the existing qualitative guidelines. The current study was undertaken to understand how different hydrocolloids affect texture and other sensory modalities of pureed carrots when viscosity is kept within a specific range. Eight hydrocolloids and one commercial sample were tested using small (rheology) and large deformation (rheology and

TPA) instrumental measurements. Sensory analysis was also conducted. Hydrocolloids showed differences in gel strength (small deformation) and ease of deformation to make a swallow-able bolus (large deformation) and similarities in elastic behaviour. Trained panel sensory results indicated textural similarities among some hydrocolloids. Partial napping gave a product map and associated descriptors of each hydrocolloid for appearance, flavour and texture. Hydrocolloids with similarities in texture differed in appearance and flavour. This data can be used for understanding the impact of hydrocolloids on foods for individuals with dysphagia.

ACKNOWLEDGEMENTS

This thesis would not have been possible without the support and guidance of my advisor Dr. Lisa Duizer. It was only because of her trust and confidence in me which made all the stages of this research a great learning cum enjoyable experience. You made me love sensory and gave the much needed encouragement with ‘positive reinforcement’ at all times. It was only because of your constant guidance that now statistics seems so much more interesting. Thank you Lisa for editing and re-editing my work which gave the thesis such a great look. I owe my deepest gratitude to Dr. Milena Corredig, my advisory committee member, who has always been there to clarify all my doubts. Thank you Milena for guiding me to analyse all the rheology data and spending so much time in improving my thesis. I will always remember you for helping me anywhere and anytime, taking time off from your busy schedule and investing the same in me, be it just after your knee surgery or in-between conference meetings. I feel myself to be lucky to have Lisa and Milena as my advising gurus.

I am indebted to Eleana Kristo, for always supporting me and making me comfortable in using rheometers and answering all my questions. Whenever I had the slightest doubt, I would just run to you and you were always there to help me, even during your maternity leave!!!!! I will never forget your caring and calm attitude and your smiling face even though I always had bag full of questions for you.

I would like to thank CP Kelco, Ingredion Inc., GIC and Marsan Foods for supplying the hydrocolloids and commercial product for testing in this research.

Thank you to my colleagues and friends who have helped me in every possible way from sensory setting to making me understand statistics. The huge amount of work involved in arranging everything for sensory evaluation became easy only because of my lab mates. Patti, Stefanie, Elizabeth, Thais and Nicholas, I will always remember the fun we had while working together in the kitchen and preparing so much purees.

This whole process has been a smooth sailing with the blessings of my parents and in-laws. A big thanks to my husband and lovely kids for always being supportive, appreciative and being around whenever I needed them. I know that they have been eagerly waiting for this moment and are more excited about me achieving this milestone in my life. Thank you to my family friends who have always offered to help in making this whole thing a big hit.

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TABLE OF CONTENTS ACKNOWLEDGEMENTS ...... III LIST OF TABLES ...... VII LIST OF FIGURES ...... IX LIST OF ABBREVIATIONS ...... XI 1. GENERAL INTRODUCTION ...... 1 2. LITERATURE REVIEW ...... 4 2.1 DYSPHAGIA ...... 4

2.1.1 Physiological changes and dysphagia ...... 6

2.1.2 Psychological effects of dysphagia ...... 7

2.1.3 Treatment / Management of dysphagia ...... 8

2.2 PUREED FOODS ...... 9

2.2.1 Existing standards of pureed foods ...... 11

2.3 TEXTURE ...... 15

2.3.1 Hydrocolloids as texturizing or structuring agents ...... 16

2.4 TECHNIQUES FOR MEASURING TEXTURAL PROPERTIES OF PUREED FOODS ...... 21

2.4.1 Structural properties using Rheological measures ...... 21

2.4.2 Breakdown properties using Rheology and Texture Profile Analysis ...... 27

2.4.3 Sensory properties of pureed foods ...... 31

2.4.4 Correlation of Instrumental and Sensory evaluation ...... 34 3. TEXTURAL CHARACTERISATION OF PUREED FOODS WITH HYDROCOLLOIDS USING INSTRUMENTAL TECHNIQUES ...... 37 3.1 INTRODUCTION...... 37

3.2 MATERIALS AND METHODS ...... 40

3.2.1 Materials ...... 40

3.2.2 Sample Preparation ...... 41

3.2.3 Viscosity Measurement ...... 41

3.2.4 Rheological Properties ...... 42

3.2.5 Mechanical Properties ...... 43

3.3 DATA ANALYSIS ...... 44

3.4 RESULTS AND DISCUSSION ...... 44

3.4.1 Viscosity ...... 44

3.4.2 Small Deformation Tests ...... 47

3.4.3 Texture Profile Analysis (TPA) ...... 60

3.4.4 Discussion ...... 62

3.5 CONCLUSIONS ...... 64

4. TEXTURAL CHARACTERISATION OF PUREED CARROTS WITH HYDROCOLLOIDS USING SENSORY TECHNIQUES OF NAPPING® AND DESCRIPTIVE ANALYSIS ...... 65 4.1 INTRODUCTION...... 65

4.2 MATERIALS & METHOD ...... 67

4.2.1 Samples ...... 67

4.2.2 Sensory Evaluation ...... 68

4.2.3 Data Analysis ...... 72

4.3 RESULTS AND DISCUSSION ...... 74

4.3.1 Effect of hydrocolloids on Appearance, Flavour and Texture of pureed carrots: 74

4.3.2 Effect of hydrocolloids on texture of pureed carrots: ...... 90

4.3.3 Comparison of trained panel and Napping® (texture) results ...... 93

4.4 CORRELATIONS OF INSTRUMENTAL AND SENSORY MEASUREMENTS ...... 94

4.5 CONCLUSION ...... 98

5. OVERALL CONCLUSIONS AND RECOMMENDATIONS ...... 99 REFERENCES ...... 104 APPENDIX A - ANOVA TABLES OF INSTRUMENTAL PARAMETERS IN PUREED CARROTS USING DIFFERENT HYDROCOLLOIDS ...... 137 APPENDIX B – FACTOR LOADINGS FOR HYDROCOLLOIDS AS OBTAINED IN PARTIAL NAPPING ...... 142 APPENDIX C - ANOVA TABLE OF SENSORY TEXTURE ANALYSIS OF PUREED CARROTS MADE WITH DIFFERENT HYDROCOLLOIDS...... 145

LIST OF TABLES

Table 2.1 - Hydrocolloids used in food industry...... 17

Table 3.1 - Concentration of each hydrocolloid matched with viscosity values of ThickenUp® at shear rate 41-50 s-1...... 42

Table 3.2 - Apparent viscosity measured at three shear rates (10, 50 and 100 s-1) measured at 55°C for pureed carrot formulations with different hydrocolloids...... 46

Table 3.7 - Results of Texture Profile Analysis (TPA) using TA.XT plus Texture Analyser for pureed carrots using different hydrocolloids...... 61

Table 4.1 – Attributes evaluated by trained panel with definition and references used along with their intensity values on a 15cm line scale...... 71

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Table 4.2 - Eigen values and percent of variance for major dimensions of partial napping (appearance) using multiple factor analysis...... 76

Table 4.3 - Correlation of attributes / descriptors (supplementary variables) with first four dimensions of Multiple Factor Analysis for Partial Napping (Appearance)...... 77

Table 4.4 - Eigen values and percent of variance for major dimensions of partial napping (Flavour) using multiple factor analysis...... 80

Table 4.5 - Correlation of attributes / descriptors (supplementary variables) with first four dimensions of Multiple Factor Analysis for Partial Napping (Flavour)...... 81

Table 4.6 - Eigen values and percent of variance for major dimensions of partial napping (Texture) using multiple factor analysis...... 84

Table 4.7 - Correlation of attributes / descriptors (supplementary variables) with first four dimensions of Multiple Factor Analysis for Partial Napping (Texture)...... 85

Table 4.8 - Summary of attributes obtained for three tested sensory modalities of pureed carrots formulations with different hydrocolloids using partial napping...... 89

Table 4.9 – Mean scores and standard deviations from trained panel for pureed carrot formulations with different hydrocolloids...... 91

Table 4.10 - Correlation of instrumental measures with sensory attributes...... 96

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LIST OF FIGURES

Figure 2.1 - Stages Of Swallowing...... 5

Figure 2.2 - Food Texture Modification Scale...... 12

Figure 2.3 – Existing Guidelines For Pureed Foods ...... 14

Figure 2.4 - Relationship Of Texture With Rheology And TPA...... 16

Figure 2.5 - Example Of Determining Linear Viscoelastic Region Using Strain Sweep. .... 23

Figure 2.6 - Stress Response To Applied Strain Deformation With Phase Angle...... 24

Figure 2.7 - Complex Modulus (G*) And Phase Angle (Δ) Are A Function Of Elastic Modulus (G´) And Viscous Modulus (G´´)...... 25

Figure 2.8 - Rheological Characterisation Of Safe-Bolus...... 26

Figure 2.9 - Texture Profile Analysis – Instrumental Parameters Obtained And Their Sensory Significance...... 29

Figure 3.1 - Shear Thinning Behaviour Of Pureed Carrot Formulations With Different Hydrocolloids. Apparent Viscosity Was Measured With Shear Rate Ramp From 1 – 150 s-1 In 8 Min At 55ºC...... 45

Figure 3.2 - Variations Of Elastic (A) And Viscous Modulus (B) As A Function Of Strain For Mixtures Of Pureed Carrots Containing Different Hydrocolloids, At Various Concentrations To Obtain a Viscosity At 50 s-1 Of About 3 Pa s...... 50

Figure 3.3 - Variations Of Elastic (A) And Viscous Modulus (B) As A Function Of Frequency For Mixtures Of Pureed Carrots Containing Different Hydrocolloids, At Various Concentrations To Obtain A Viscosity At 50 s-1 Of About 3 Pa s...... 54

Figure 3.4 - Average Values Of Two Replicates For (A) Elastic Modulus - G´ And (B) Viscous Modulus - G´´ For Mixtures Of Pureed Carrots Containing Different

Hydrocolloids, At Various Concentrations To Obtain A Viscosity At 50 s-1 Of About 3 Pa s...... 58

Figure 4.1 – Structure Of Data Table For Multiple Factor Analysis For Napping ® ...... 73

Figure 4.2 - Product Map Generated Using Multiple Factor Analysis Of Appearance Data On Factor 1 And Factor 2...... 78

Figure 4.3 - Product Map Generated Using Multiple Factor Analysis Of Flavour Data On Factor 1 And Factor 2...... 82

Figure 4.4 - Product Map Generated Using Multiple Factor Analysis Of Texture Data On Factor 1 And Factor 2...... 86

LIST OF ABBREVIATIONS

LTC……………………………………………………………… Long Term Care Centres

SAOS…………………………………………………… Small Amplitude Oscillatory Shear

LVR…………………………………………………………… Linear Viscoelastic Region

TPA………………………………………………………………... Texture Profile Analysis

DA……………………………………………………………………... Descriptive Analysis

MCS (i)…………………………………………………………………... Uni-Pure® D2560

Unipure……………………………………………………………… Uni-Pure® Dys-sperse

CMC………………………………………………………………. Carboxymethyl Cellulose

PN……………………………………………………………………………. Partial napping

UFP…………………………………………………………………….. Ultra Flash Profiling

Chapter 1

1. GENERAL INTRODUCTION

Chewing and swallowing of food involves a series of regulated and time sequenced activities.

Swallowing is the outcome of the coordinated act of numerous nerves and muscles working rhythmically so as to have a safe swallow. Within healthy individuals, the act of swallowing occurs without problems. However, physiological changes related to aging, and neurodegenerative diseases such as Alzheimer’s and Parkinson’s and stroke are major precursors for the onset of dysfunction in the swallowing mechanism (Khan, Carmona, & Traube, 2014). This swallowing disorder known as Dysphagia contributes to morbidity and increased mortality in the elderly, owing to the increased risk of choking and aspiration, malnutrition and lowered immune response

(Perlman et al., 2004). According to Perlman et al. (2004) dysphagia kills more than 50,000 people per year in the United States alone. The prevalence of dysphagia in Canada is more than 200,000 persons at any given time (CASLPO, 2007). A study of long term care homes in Ontario found swallowing disorders in 68% of the residents and in another study it was found that about 30 –

45% of elderly individuals living independently have dysphagia (Roy, Stemple, Merrill, &

Thomas, 2007; Steele, Greenwood, Ens, Robertson, & Seidman-carlson, 1997).

Treatment of dysphagia is important to improve quality of life and self-esteem within individuals living with this condition (Ekberg, Hamdy, Woisard, Wuttge-Hannig, & Ortega, 2002). Modified texture foods and thickened fluids are recommended as part of the compensation strategy to aid in safe-swallow (Steele et al., 2014). These modifications address the slow reflux actions of nerves and muscles involved in the swallowing process. Texture modifications are achieved through different processes including chopping, mincing, pureeing and blending so as to have the right

1 textured food for an individual with swallowing dysfunction (Keller, Chambers, Niezgoda, &

Duizer, 2012). The use of texturing agents – hydrocolloids, is inevitable in the preparation of such modified foods because they provide uniform consistency and have shear thinning and water holding properties. The right consistency and texture are important for modified foods but current qualitative standards for pureed foods create ambiguity leading to ‘subjective’ differences in the final product. Quantifiable standards for pureed foods will help in designing right-textured foods.

Inappropriate textures have been the cause of fatal choking incidents (Jukes et al., 2012;

Berzlanovich, Fazeny-Dörner, Waldhoer, Fasching, & Keil, 2005). This is a true challenge, especially considering that dysphagia is on an increasing trend owing to an increase in life expectancy, particularly in Canada, which is currently passing through a period where the population born during the baby boom period is aging.

Existing standards specify viscosity as the sole criteria for different classifications of thickened fluids but it has been proven that there are other rheological measures which have to be taken into consideration while designing safe-swallow drinks ( Claes et al., 2012; Adeleye & Rachal, 2007;

Eleya & Gunasekaran, 2007). Qualitative standards for pureed food are based on descriptive terms such as: thick puree - thick enough to form furrows with prongs of a fork and thin puree - spreads out if spilled (British Dietetic Association, 2011; IASLT & INDI., 2009). These lay emphasis on viscosity as the criteria for deciding consistency and texture. For developing standards, it becomes imperative to understand the major factors / measures which have to be addressed for easy and smooth swallow action.

This research proposes to reduce current subjectivity by carrying out a detailed study of the rheological and sensory parameters of pureed foods prepared with different hydrocolloids. This

2 research is an investigation of the effect of selected hydrocolloids on the texture of pureed foods.

We hypothesize that there is no effect of hydrocolloid type on pureed food texture, if the viscosity is kept within a specific range.

Specific objectives of this research were:

1. To determine concentrations of hydrocolloids matched for a specific viscosity range in

pureed carrots.

2. Instrumental characterization of pureed carrots with rheological testing and Texture Profile

Analysis.

3. Sensory characterization so as to quantify important textural parameters perceived during

oral processing/swallowing.

4. To understand relations between oral processing and instrumental measurements.

Chapter 2

2. LITERATURE REVIEW

2.1 DYSPHAGIA

Chewing food, one of the most basic human responses, comes as a natural instinct. It involves both involuntary and voluntary actions which are triggered through the sight, smell and feel of food

(Koç, Vinyard, Essick, & Foegeding, 2013). Once food is chewed and the bolus is ready, the normal swallowing action is a complex, multi-stage sequence of voluntary and involuntary movements and reflexes that involve several muscles and nerves of the head and neck region

(Cichero et al., 2013; Germain, Dufresne, & Gray-Donald, 2006; Humbert & Robbins, 2008). One complete swallow act can be classified into three main stages (Figure. 2.1): Oral Preparation Stage

– where the food is masticated, mixed with saliva, formed into a bolus and propelled to the back of the oral cavity, Pharyngeal Stage – where the prepared bolus from the posterior tongue region of the mouth is pushed into the pharynx and Esophageal Stage – where several peristaltic actions in the esophagus make easy passage of the bolus to the stomach region (Garcia & Chambers, 2010;

Logemann, 2007). Dysphagia is a word of Greek origin, dys (with difficulty) and phagia (to eat)

(Koidou, Kollias, Sdravou, & Grouios, 2013). Dysphagia is a swallowing dysfunction which can affect any or all stages involved in food oral processing during the movement of the bolus from the mouth to the stomach (Logemann, 2007). Although it can affect people of all ages, it is more prevalent in the elderly population owing to physiological changes making them more susceptible to neurological diseases (Garcia & Chambers, 2010; Ekberg et al., 2002; Nilsson, Ekberg, Olsson,

& Hindfelt, 1996). Even without neurological diseases the process of aging alters an individual’s

4 sensorimotor skills and increases the time involved in each stage of swallowing ( Sura, Madhavan,

Carnaby, & Crary, 2012; Logemann, 2007).

ORAL Phase PHARYNGEAL Phase1

ESOPHAGUS Phase PHARYNGEAL Phase 2

Figure 2.1 - Stages of Swallowing (Garcia & Chambers, 2010).

Dysphagia can, therefore, be a consequence of anatomical and physiological changes occurring with age or as a result of various degenerative neurological disorders such as Parkinson’s,

Alzheimer’s, multiple sclerosis, congenital abnormalities, dementia, various forms of cancer (such as head and neck cancer, cancer of the brain, nose, oral cavity, pharynx, larynx, and esophagus), severe head trauma and cardiovascular conditions ( Easterling & Robbins, 2008; CASLPO, 2007;

Logemann, 2007; Terrado, Russell, & Bowman, 2001). It can also occur as a consequence of medical interventions such as stomach stapling or following head and / or neck surgery and as a side-effect of neuroleptic medications or the insertion of a tracheostomy tube (CASLPO, 2007).

2.1.1 Physiological changes and dysphagia

The upper aerodigestive tract is involved both in swallowing and breathing mechanisms; therefore it is important that there be balanced coordination of these two activities for a safe swallowing action ( Forster, Samaras, Gold, & Samaras, 2011; CASLPO, 2007; Cichero & Atherton, 2007).

The pharynx acts as a passage for airflow and food. It is dilated during breathing and constricted during swallowing while pushing the bolus into the esophagus (Matsuo & Palmer, 2009). While swallowing, various mechanisms close the airway path of the pharynx so that it can be used only for the passage of food. Any irregularity or poor coordination in this activity can lead to trickling of food particles to the trachea and into the lungs.

The aerodigestive tract undergoes structural and functional changes with aging which can result in swallowing dysfunction (Roy et al., 2007). Motor skills, gestures and coordination are weakened in older adults leading to slow, delayed or ineffective reflex action (Kendall & Leonard, 2001;

Nilsson et al., 1996; Tracy et al., 1989). The time of bolus formation and its passage through the pharynx increases with age but in dysphagia the aryepiglottic fold closure relative to pharyngeal

6 bolus transit is delayed affecting proper closing and opening of the airway (Sura et al., 2012;

Kendall & Leonard, 2001). This causes liquid or food to enter the airway below the vocal folds leading to choking, asphyxiation, or aspiration pneumonia which may be fatal in some cases (Ney,

Weiss, Kind, & Robbins, 2009; Samuels & Chadwick, 2006). It causes respiratory infections and poor oral hygiene condition (Ekberg et al., 2002; Steele et al., 1997).

Dysphagia is also a common consequence of acute stroke, developing in 50% to 75% of stroke cases. This then leads to other severe complications such as aspiration, malnutrition, and pneumonia (Teasell, Martino, Richardson, Bhogal, & Speechley, 2013; Ney et al., 2009).

2.1.2 Psychological effects of dysphagia

Dysphagia brings anxiety, stress and panic during mealtimes leading to loss of appetite (Ekberg et al., 2002). It causes major social discomfort as individuals with dysphagia feel embarrassed being unable to perform the basic task of ‘eating’. This results in decreased self-esteem, poor physical and mental health and irritated behavior (Forster et al., 2011; Roy et al., 2007; Ekberg et al., 2002).

Individuals with dysphagia prefer to eat alone and tend to stay away from celebrations such as social and family gatherings during festivals and holidays where ‘eating and drinking’ are an integral part (Ekberg et al., 2002). They prefer to stay in isolation, with 25 – 36% of elders with dysphagia confirming fear of socializing (Leow, Huckabee, Anderson, & Beckert, 2010; Ekberg et al., 2002). This causes depression – a feeling that they can never get cured, leading to the onset of a vicious cycle of low appetite, dehydration, malnutrition, and reduced physical activity leading to death in some cases. In a study analyzing the social and psychological consequences of dysphagia, it was found that 41% of subjects experienced ‘anxiety’ during mealtimes. More than

50% of subjects confirmed a ‘lowering of diet intake’ with 44% confirming weight loss. Only 39% believed this condition to be ‘treatable’(Ekberg et al., 2002).

Reduced food intake leads to weight loss, dehydration and malnutrition. These conditions weaken the immune system making older adults more prone to illness and / or disabilities (Terrado et al.,

2001). This also contributes to lethargy and reduced mobility leading to a deterioration of cognitive skills and internal organ functions (Heiss, Goldberg, & Dzarnoski, 2010; Leow et al., 2010).

2.1.3 Treatment / Management of dysphagia

Considering the adverse implications of dysphagia along with a rise in the number of people being affected each year and the subsequent economic burden; its management is of core importance.

The treatment course to be adopted depends on its evaluation by a speech language pathologist using non-instrumental techniques including bedside screening and instrumental techniques such as video fluoroscopy, endoscopy, ultrasound, and manometry (Koidou et al., 2013; Ney et al.,

2009). A number of treatments have been suggested including active exercise so as to strengthen tongue, head and neck muscles, changes in the swallowing act such as eating small volumes, double swallow, postural correction therapy such as sitting upright at 90°, sitting upright or keeping the head of the bed elevated for 30-45 minutes after eating and compensation strategies

(Ecker, Eiss, & Lements, 2008; Humbert & Robbins, 2008; Logemann, 2008; Terrado et al., 2001).

Compensation strategies aim at improving diet and nutritional intake and provide proper hydration

(Sura et al., 2012; Logemann, 2008). The most common treatment in this category includes the prescription of modified texture foods and thickened fluids. Modified food texture improves the safety of swallowing (Speyer, Baijens, Heijnen, & Zwijnenberg, 2010). Dietary modification— altering the consistency of foods and liquids—is a fundamental aspect of dysphagia, and the degree

8 of dietary modification is based on each patient’s swallowing capacity (Garcia & Chambers, 2010).

This change in consistency of foods and/or drinks slows down the process of swallowing and allows a better control of bolus transportation through the pharynx (Quinchia et al., 2011; Penman

& Thomson, 1998). Proper assessment and correct textures are important for maintaining adequate nutritional intake and swallowing safety (Terrado et al., 2001).

2.2 PUREED FOODS

Pureed foods, as the name implies, are foods that have been blended and / or ground to a form which requires less chewing and oral manipulation to make a cohesive bolus (Hotaling, 1992;

Curran & Groher, 1990). This bolus is easy to push with the tongue into the pharynx, thus making swallowing easy (Keller et al. 2012). Pureed foods are a class of modified texture foods which are mainly prescribed for oropharyngeal dysphagia – a condition where the oral and motor muscles related to biting and chewing are weakened (Keller et al., 2012). These foods are soft, smooth and semi-solid, mechanically altered with or without the addition of texturizing agents and / or liquids such as water, milk, juice, or gravy, during preparation. Foods with modified texture are the best choice for people with impaired swallowing to help maintain regular diet and nutrition. These are made either in-house or available commercially in bulk or individual-portion size (Ettinger &

Duizer, 2014). The degree of texture modification – pureed and minced, varies according to the severity of dysfunction in the swallowing mechanism. This is decided based on an evaluation by a speech language pathologist and then given as per the recommendations of a dietitian / nutritionist (Garcia & Chambers, 2010). The right texture is of utmost importance for pureed foods for safety. If the food is “too thin”, it will flow rapidly through the oropharyngeal region without proper control and will lead to aspiration risk. If the food is too thick, it will not be completely

9 pushed in the pharynx region leading to choking or residue-after-swallow (Cichero et al., 2013;

Curran & Groher, 1990). Currently pureed foods are the source of food intake in 15-30% of residents in long-term care settings (Keller et al., 2012; Hotaling, 1992).

While the importance of pureed diets for management of dysphagia is well-recognized, research in the past has focused on what should not be included such as nuts, raw fruits & vegetables and stringy foods. At the present time the definition of pureed foods is qualitative and subjective.

For instance, the criteria of a pureed food to be served in long term homes in Canada is based on eye-ball judgment after pureeing / blending regular menu-foods in a food processor. These criteria include not oozing or not spreading on plate (Ilhamto, Anciado, Keller, & Duizer, 2014; Garcia

& Chambers, 2010). Texture is typically characterized by terms such as not too sticky, no large pieces, not too thin (Ilhamto et al., 2014). The lack of objective standards leads to differences in consistency across brands of commercial pureed foods (Ettinger & Duizer, 2014). Additionally, within long term care homes, this leads to differences in consistency of final pureed food, between nutrition managers and cooks and also between individual cooks, resulting in foods of different textures being served to dysphagia individuals (Keller & Duizer, 2014a; Ilhamto et al., 2014). The difference in texture is also observed by the consumers (Keller & Duizer, 2014b). Textures have variously been described as stringy, sticky, gritty, thick and rubbery, with consistency ranging from watery to dry.

Inappropriate texture of modified foods can lead to choking and, asphyxiation, highlighting the importance of the correct texture of pureed foods for safety and efficacy (Jukes et al., 2012;

Berzlanovich et al., 2005). In some cases this can lead to death of an individual.

2.2.1 Existing standards of pureed foods

Increased demand for pureed foods and unwarranted consequences of feeding improper texture has been recognized globally at all levels of dysphagia management. Until recently, each nursing center was using its own set of descriptors leading to extreme confusion during patient transfer from one center to the other (Cichero & Atherton, 2007). In order to have clarity about the appropriate consistency among all the parties involved and uniformity in terminology across various institutions and organizations, standards have been developed in a few countries for thickened fluids and modified foods. Diet descriptors for dysphagia in each of these countries were outlined through conferences and focus group meetings with speech language pathologists, dietitians, nurses, food service staff, commercial companies, training institutes for dietitians and nurses and scientists (Cichero & Atherton, 2007; Robbins, Kays, & Mccallum, 2007). Literature reviews and current practices being followed were the basis of classification (Cichero & Atherton,

2007). The absence of relevant scientific evidence has been acknowledged in these documents and while there exists some objective measures for thickened fluids (viscosity) and minced foods

(particle size), the standards for pureed foods are ‘purely subjective’ with ‘descriptive words’

(Cichero et al., 2013; IASLT & INDI., 2009). These descriptors have overlapping terms which create confusion and hence inconsistencies in the food being served. For example, in the United

States, one of the descriptions for Dysphagia Pureed is ‘very cohesive’ and for Dysphagia

Mechanically Altered is ‘cohesive’, clearly bringing in the factor of subjectivity in the final product. Visual judgment is the means of assessing the consistency specified in these standards

(Robbins et al., 2007) which also leads to subjectivity. There is a need to have objective standards for pureed foods similar to those developed for thickened liquids.

Generally the scale / spectrum for texture modification (Figure. 2.2) ranges from regular foods / unmodified texture to a liquidized variant (IASLT & INDI., 2009). Guidelines exist, although not very sophisticated, for texture modification, with particle-size being specified in some countries

(such as Ireland, the UK, USA and Australia) for minced foods, but for pureed foods it is totally descriptive. It is characterized with terms like thick puree, thin puree, puree, smooth puree, dysphagia pureed, semi-pureed and liquidized (Cichero et al. 2013; Keller et al. 2012). These words show that viscosity is a key aspect of pureed foods. However, to date, viscosity is purely a subjective term and has not been measured objectively in pureed foods.

Regular Minced Pureed Thickened Foods Foods Foods Fluids

Figure 2.2 - Food Texture Modification Scale (IASLT & INDI., 2009).

In Canada, the national guidelines for texture modified foods are at the development stage, with each province following descriptors provided by its health services ( Keller & Duizer, 2014a;

Alberta Health Services, 2012; Houjaij, Dufresne, Lachance, & Ramaswamy, 2009). It is an irony that although the number of people requiring modified texture foods is more than those requiring thickened fluids, there are no quantitative standards for the former (Steele et al., 1997). Figure 2.3 outlines standards developed in a number of countries. It highlights the different terms used for

12 describing pureed foods. This has been well recognized and led to a global initiative by group of volunteers from diverse professions including nutrition & dietetics, medicine, speech pathology, occupational therapy, nursing, patient safety, engineering, food science & technology from around the world to work together to establish an international standardized terminology and definitions for texture modified foods and thickened liquids for persons with dysphagia – International

Dysphagia Diet Standardization Initiative (IDDSI; web address: www.iddsi.org) (Cichero et al.,

2013). The need for scientific-based and instrumental objective standards for pureed foods has been highlighted in the first document released by IDDSI. Canada’s interest is evident from the fact that the inaugural meeting of IDDSI took place in Toronto in June 2012.

The right texture of pureed foods is important for ‘safety’ and ‘liking’ by the population for whom it is meant. If modified foods are not liked by consumers, the whole purpose of providing pureed foods, to maintain regular diet and nutritional intake, will be lost. Pureed foods are never the first choice but have to be taken for maintaining good health, similar to a medical prescription (Keller

& Duizer, 2014a). These foods are often referred as baby food, unnatural, unappealing, tasteless and bland (Keller & Duizer, 2014a). A study by Keller et al (2014) reveals a strong dislike for pureed foods, resulting in poor intake and weight loss. The reluctance towards pureed foods is further strengthened due to lack of choices (Germain et al., 2006). This calls for instrumental and sensory testing to understand and obtain desired results. If texture is described quantitatively using important parameters from a swallowing point of view, it will increase safety and efficacy, reduce confusion among the personnel involved directly and indirectly and give clear guidelines to industries. The demand and importance of quantitatively classifying modified texture foods

(Wendin et al., 2010; Houjaij et al., 2009) is increasing.

Figure 2.3 – Existing guidelines for Pureed Foods ( Cichero et al., 2013; Keller et al., 2012; British Dietitic Association, 2011; IASLT & INDI., 2009; Cichero & Atherton, 2007)

2.3 TEXTURE

Texture has been defined as ‘‘the sensory and functional manifestation of the structural, mechanical and surface properties of foods detected through the senses of vision, hearing, touch and kinesthetics’’ (Szczesniak, 2002). Within all food attributes, texture has been deemed to be an important attribute (Funami, 2011; Kealy, 2006). In addition, the right texture in pureed foods is critical as these are “the foods” available for individuals with swallowing dysfunction which are safe to swallow. Pureeing food however modifies the structure and changes the original properties of the food so as to make it easier to swallow. It is important to understand how these modifications affect the swallowing mechanism and sensory perception. Understanding the physical structure of pureed foods, mechanical properties and microstructure gives an insight as to how it is perceived in the initial stages of eating (Pascua, Koç, & Foegeding, 2013; Chen, 2009).

During oral processing, food is subjected to mastication resulting in deformation and flow throughout the swallowing and digestion process. Information about this behavior can be gained by rheological testing and texture profile analysis (TPA) (Chen & Stokes, 2012). It has been proven through computer simulation techniques that the rheological properties of fluids influence bolus transportation through the pharynx (Meng, Rao, & Datta, 2005). Commercial thickened liquids within a specific viscosity range such as those with custard, honey-thick consistencies can vary greatly with regard to viscoelastic properties – underlining the importance of including rheological parameters in designing foods for dysphagia (Payne, Methven, Fairfield, & Bell, 2011). Initial perception of texture is based on its rheological properties and subsequent breakdown of food is based on mechanical attributes which are measured by Texture Profile Analysis (Figure. 2.4)

(Chen & Stokes, 2012; Funami, 2011; Borwankar, 1992).

Figure 2.4 - Relationship of texture with rheology and TPA (Borwankar, 1992).

2.3.1 Hydrocolloids as texturizing or structuring agents

Hydrocolloids or hydrophilic colloids refer to those polysaccharides and proteins which have distinct characteristics of thickening, gelling and stabilizing solutions, emulsions and foams (Saha

& Bhattacharya, 2010). The long polymer chain and high molecular weight of hydrocolloids make them suitable for a number of applications in food even at concentrations below 1% such as to inhibit ice crystal formation, to control flavor release, and to prevent sedimentation (Williams,

2006). In pureed foods, hydrocolloids are used as texturizing agents to give desired consistency and to control syneresis. While providing these functional properties, textural and sensorial differences occur due to hydrocolloid type, molecular structure and concentration. An insight into the behavior of hydrocolloids will help in formulating the right-textured pureed foods with acceptable sensory properties. Various sources of hydrocolloids (Table 2.1) include plants, plant exudates, seeds, animals, seaweed as well as microbial sources (Milani & Maleki, 2012).

Table 2.1 - Hydrocolloids used in food industry (Milani & Maleki, 2012).

Source Hydrocolloid

Modified Corn Starch

Plant Cellulose and its derivatives

Pectin

Gum Arabic

Plant Exudate Gum Ghatti

Gum Karaya

Guar Gum Seed Locust Bean Gum

Xanthan Microbial Gellan

Carrageenan

Seaweed Alginates

Agar

Chitin and Chitosan Animal Gelatin

2.3.1.1 Starch

Starch, the most commonly used hydrocolloid thickener in pureed food, consists of two polysaccharides – amylose and amylopectin. Both amylose and amylopectin consists of linear α

(1, 4) linked glucopyranose units, with amylopectin having extensive branching via (1, 6) linkages

17 while amylose is almost linear-chain molecule (Rapaille & Vanhemelrijck, 1997). Both molecules have high molecular weight and are present in an aggregated state. Starch occurs naturally as granules, with size ranging from 2-100 µm depending on the source (BeMiller & Whistler, 1996).

Swelling of granules attribute different properties to starch which is a characteristic of its source

(corn, potato, rice, wheat) and amylose content (Mandala, 2012). Native starch is very sensitive to shear. Once the granules are hydrated, they get swollen and peak viscosity is reached. These get ruptured by shear and increase in temperature resulting in sudden decrease of viscosity (BeMiller

& Whistler, 1996). Modification of starch is done to withstand the effects of adverse processing conditions while maintaining the desired thickening and gelling properties (Murphy, 2000). That is why often modified starch is used, as crosslinking allows for a higher resistance to shear.

Modified starch has been used in thickened fluids commercially and as a thickener in pureed foods in Long Term Care Centers (LTCs).

2.3.1.2 Cellulose Derivatives

Cellulose is the world’s most abundant naturally occurring polymer present in plant cell walls. It is a high molecular weight linear polymer of β (1, 4) linked glucopyranose (Williams, 2006). The hydroxyl groups on the glucose residues are substituted by etherification by reacting with appropriate reagent to obtain water-soluble cellulose derivatives, suitable for applications in food

(Zecher & Gerrish, 1997). These derivatives include methyl cellulose - MC (methyl chloride as reactant), methyl hydroxypropylcellulose (methyl chloride and propylene oxide as reactant) and sodium carboxymethylcellulose - CMC (sodium chloroacetate as reactant) (Zecher & Gerrish,

1997). The strong water binding capability of CMC makes it an important ingredient for

18 minimizing water exudate or syneresis (Zecher & Gerrish, 1997). MC and CMC have been recently used to thicken fluids for dysphagia (Damodhar, 2011).

2.3.1.3 Pectin

Pectin is an anionic heteropolysaccharide consisting of galacturonic acid units with α (1, 4) bonds as backbone and interrupted by the insertion of 1, 2-linked L-rhamnose in adjacent or alternative positions (Funami, 2010). They are classified as high methoxyl pectin (HM) or low methoxyl pectin (LM) depending on the degree of esterification of carboxyl groups, present in galacturonic acid, with methanol (May, 1997). Conventional sources of pectin include citrus peel and apple pomace. Alternative sources include sugar beet pulp, sunflower heads and mango waste

(Srivastava & Malviya, 2011). Both HM and LM pectin have been studied to understand the effect on swallowing pressure and sensory properties when used to prepare thickened fluids for people with swallowing disorders (Damodhar, 2011). Sugar beet pectin has acetyl group, ferulic acid and protein moieties in its structure, which make it a potential oil-in-water emulsifier (Siew &

Wiiliams, 2008).

2.3.1.4 Xanthan Gum

Xanthan gum is an extracellular anionic heteropolysaccharide secreted by the micro-organism

Xanthomonas campestris (Urlacher & Noble, 1997). It is a high molecular weight gum with a cellulosic backbone of β - (1→4) linked D-glucose units having two mannose and one glucuronic acid on every other glucose residue (Williams, 2006). The terminal mannose residue is pyruvated while the non-terminal mannose residue at the backbone is acetylated (Williams, 2006). It forms a weak network with coil-helix transition, a stiff 5-fold helical structure with the side-chains folded

19 in and associated with the backbone (Williams, 2006). Xanthan gum has been extensively studied for use in dysphagia diets (Cichero, 2013; Funami, Ishihara, & Nakauma, 2012; Damodhar, 2011;

Nakauma, Ishihara, Funami, & Nishinari, 2011; Nishinari et al., 2011; Sworn, Kerdavid, & Fayos,

2008).

2.3.1.5 Gellan Gum

Gellan gum is a bacterial (Sphingomonas elodia) heteropolysaccharide consisting of a linear tetra saccharide repeat unit of β (1,3) glucopyranose, β (1,4) glucuronopyranose, β (1,4) glucopyranose and α (1,4) rhamnopyranose (Williams, 2006). It is available in two forms – high-acyl and low- acyl gellan gum. High-acyl is the native form of gellan gum with two acyl substituents – acetate and glycerate while in low-acyl form, the acyl groups are absent (Milani & Maleki, 2012). This causes differences in the type of gel formed, with the native form forming soft elastic gels and de- acylated material forming hard brittle gels (Williams, 2006). The gelation mechanism involves a disorder-order transition from coil to helix-form. Low-acyl gellan gum forms gels in the presences of cations while high-acyl gellan gum is capable of forming self-supporting gels (Sworn, 2000).

Gellan gum is being studied for use in dysphagia diets and also used commercially in dysphagia pureed diets (Med-Diet Inc., 2014, Trisco Foods, 2014; Funami, Ishihara, Nakauma, Kohyama, &

Nishinari, 2012). It is being used in pharmaceutical formulations to aid in easy swallow (Anupama,

Kiran, & Rao, 2015).

2.3.1.6 Carrageenan

Carrageenan, a hydrophilic charged (anionic) polysaccharide, obtained from certain species of red seaweed (Rhodophyceae class) is a high molecular weight linear polysaccharide consisting of

20 repeating galactose units and 3, 6-anhydrogalactose both sulphated and non-sulphated, joined by alternating α-(1,3) and β-(1,4) glycosidic linkages (Thomas, 1997). The three types of carrageenan used in the food industry, namely kappa, iota and lambda, differ in their degree of sulphation, having one, two and three sulphate ester groups respectively. This results in differences in gel strength, texture, solubility and synergises (Funami, 2010; Campo, Kawano, Silva, & Carvalho,

2009). All are soluble in water and hybrids of carrageenan are being increasingly used to obtain desired characteristics (Williams, 2006). The gelation mechanism involves conformational transition of coil to helix and further self-association of helices resulting in three dimensional gel structure (Williams, 2006). Kappa- and iota- carrageenan have been studied for use in dysphagia thickened fluids (Cichero, 2013; Damodhar, 2011) and are used in commercial frozen treats

(pudding consistency) for dysphagia, along with other gums and starches

(http://www.lyonsreadycare.com/treats.html).

It has been shown that fluids with similar apparent viscosities flow differently, signifying the importance of viscoelastic properties in thickened fluids (Payne et al., 2011). Similar studies on pureed foods will give idea about important textural parameters to be considered while making standardized pureed foods.

2.4 TECHNIQUES FOR MEASURING TEXTURAL PROPERTIES OF PUREED FOODS

2.4.1 Structural properties using Rheological measures

Rheology is the science of flow and deformation, describing how a product deforms or flows under an applied stress (Melito & Daubert, 2011; Tabilo-Munizaga & Barbosa-Cánovas, 2005). The two extremes of material behaviour are solid-like i.e., elastic and liquid-like i.e., viscous. Most foods and all pureed foods are non-Newtonian in nature exhibiting viscoelastic properties – a

21 combination of elastic and viscous properties (Foegeding et al., 2011). Addition of hydrocolloids

/ thickeners in the form of starch, gum or a combination of starch and gum is an integral part of pureed foods (Funami, Ishihara, Nakauma, et al., 2012). Hydrocolloids, in pureed foods, aid in holding water, shear thinning, stabilizing while providing desired consistency and cohesion resulting in texture modification (Funami, 2011). This makes pureed foods a gel-system and imparts viscoelastic properties which can be understood using instrumental measures.

2.4.1.1 Small Amplitude Oscillatory Shear

Information about a pureed foods’ viscoelastic properties, can be obtained from dynamic oscillatory rheological tests also known as Small Amplitude Oscillatory Shear (SAOS) (Fischer

& Windhab, 2011). Results from these tests will give an idea about the primary structure of food,

These tests are non-destructive in nature, i.e., the strain deformations are low enough that the material structure is not broken down (Weitz, Wyss, & Larsen, 2007). This explains the elastic and viscous characteristics giving information about microstructure which play an important role in mechanical behaviour, breakdown pattern and sensory perception (Çakır et al., 2012; Coster &

Schwarz, 1987).

The small strain range where the structure is not destroyed, known as linear viscoelastic region

(LVR) is the region where material exhibits a linear relationship between stress and strain before going to the non-linear region. For this a strain sweep at fixed frequency is performed by increasing the amplitude of strain and finding the region where strain response is linear to the applied stress or LVR (Figure. 2.5).

Figure 2.5 - Example of determining Linear Viscoelastic Region using Strain Sweep.

An oscillatory test in the LVR over a range of frequencies (Frequency Sweep) gives data about various parameters which explain material behaviour (Hyun et al., 2011). These include elastic or storage modulus (G´), viscous or loss modulus (G´´), complex modulus (G*) and phase angle (δ).

In this test, a deformation is applied and the resulting stress response is measured (Figure 2.6).

Phase angle measures the difference between deformation applied and response measured in material. In the case of a perfect elastic, solid stress is proportional to deformation (δ = 0º) and for an ideal viscous fluid, stress and deformation are out-of-phase (δ = 90º). For viscoelastic material, phase angle varies between 0º to 90º.

Elastic Stress Behaviour

Stress

Figure 2.6 - Stress response to applied strain deformation with phase angle.

The elastic modulus (G´) is the energy stored in the system during shearing while the viscous modulus (G´´) represents the energy dissipated leading to permanent deformation during shear. If

G´ is much higher than G´´, it behaves solid-like and if G´´ is higher than G´, material property is more liquid-like (Tabilo-Munizaga & Barbosa-Cánovas, 2005). Dependency of these moduli on frequency gives an idea about the strength of gel-system.

Complex modulus is a measure of material stiffness and rigidity (Payne et al., 2011; Mezger,

2006). It takes into account both elastic and viscous factors as shown in Equation 2.1 and Figure

2.7 (Mezger, 2006).

(2.1)

Figure 2.7 - Complex modulus (G*) and phase angle (δ) are a function of elastic modulus (G´) and viscous modulus (G´´) (Mezger, 2006, pg 120).

Coster & Schwarz (1987) suggested classification of foods and drinks meant for people with swallowing disorders based on two parameters – viscosity range and elasticity range (Figure. 2.8).

Both of these parameters have an important role in the food sample (starting material) and the way they get changed in the entire oral manipulation cycle until a swallowable bolus is achieved. It

25 depicts that both viscosity and elasticity should be within a specific range and also should be in specific relation to each other when food is ready to be swallowed.

Figure 2.8 - Rheological characterisation of safe-bolus (Coster & Schwarz, 1987).

Wendin et al. (2010) suggested using elasticity as the rheological basis for classifying modified foods based on instrumental and sensory evaluation of commercial foods for dysphagia. Similarly

Funami et al. (2012) emphasized the importance of elasticity as a contributor to mechanical cohesiveness in non-Newtonian fluids. Casanovas et al. (2011) in their study highlighted the importance of viscoelastic behaviour of bolus on swallowing and used shear thinning behavior, thixotropic and viscoelastic characteristics of commercial dysphagia foods for cluster classification. Optimization of viscoelastic parameters is important for designing foods for

26 dysphagia in order to have a cohesive bolus flow (Funami, Ishihara, Nakauma, et al., 2012;

Ishihara, Nakauma, Funami, Odake, & Nishinari, 2011b).

2.4.2 Breakdown properties using Rheology and Texture Profile Analysis

According to Chen (2009), material properties and material strength of a food is the prime factor responsible for oral processing. Since the structure of food is totally destroyed while chewing and subsequent swallowing, it is important to understand its breakdown properties (Foegeding et al.,

2011; Chen, 2009; Kealy, 2006). This information can be obtained from yield stress measurements and texture profile analysis (TPA).

2.4.2.1 Yield Stress

Pureed foods can be categorised either as soft-foods, with reduced particle-size which are easy to swallow or as semi-solid foods. These foods are compressed between the tongue and the palate and have substantial yield stress ( Pascua et al., 2013; Claes et al., 2012; Funami et al., 2012).

Yield stress measures the strength of the internal structure of a material. It represents that stress / force which causes irreversible deformation leading to flow after the internal structure has been ruptured (Funami et al., 2012; Sun & Gunasekaran, 2009; Tabilo-Munizaga & Barbosa-Cánovas,

2005). Cohesiveness is an important criterion for safe-swallow, representing internal binding of structure, and it has been is related to yield stress; hence, it has been stated to be ‘the rheological criterion’ for dysphagia foods (Zargaraan, Rastmanesh, Fadavi, Zayeri, & Mohammadifar, 2013;

Nakauma et al., 2011).

2.4.2.2 Texture Profile Analysis

Texture profile analysis (TPA) was created to mimic human mastication behaviour (Rosenthal,

2010). The sample is compressed two times in a reciprocating action to follow jaw action giving information about five primary textural attributes of hardness, cohesiveness, adhesiveness, springiness and brittleness through a force-deformation curve (Rosenthal, 2010). Secondary textural attributes of gumminess and chewiness can be derived using primary attributes (Bourne,

2002). The sample is compressed with a certain load and its resistance to deformation is measured in the form of stress developed. It is then removed and again compressed for a ‘two-bite’ cycle.

Any tension due to stickiness is measured while removing the load after the first bite.

B H H

D E G J A C D E G I J L A C I F F K

B TPA Instrumental Definition (From Sensory Definition Parameter Fig. above) Force required to compress food with the Hardness Length BC tongue in the first compression cycle

Force required to pull food away from the Adhesiveness plunger, represented by negative force Length EF during completion of first bite

Internal strength of food which makes it hold together in a bolus is represented by 퐴푟푒푎 표푓 ∆퐺퐻퐽 Cohesiveness ratio of positive force area of second bite to Area of ∆ABD the positive force area of second bite

퐿푒푛푔푡ℎ 퐻퐼

Extent to which a food returns to its original 퐿푒푛푔푡ℎ 퐵퐶 Springiness size after being deformed in the first bite OR 푇𝑖푚푒 퐺퐼

푇𝑖푚푒 퐴퐶

Energy required to make a semi solid food Gumminess Hardness X Cohesiveness into swallow able bolus

Energy required to make a solid food into Hardness X Cohesiveness X Chewiness swallow able bolus Springiness

Figure 2.9 - Texture Profile Analysis – Instrumental parameters obtained and their sensory significance (Rosenthal, 1999).

(Rosenthal, 1999). The parameters measured with the texture analyser along with its instrumental and sensory importance considering oral processing is illustrated in Figure 2.9 (Rosenthal, 1999).

This test acts as a bridge between measurable parameters and subjective evaluations of a material

(Chen & Opara, 2013). TPA is used for texture measurement in various foods to know the effect of various treatments on sensory perception (Fernandez, Alvarez, & Canet, 2006). This technique has been used to capture differences in texture of sweet potato puree made with different hydrocolloids (Truong, Walter, & Hamann, 1997). The importance of the TPA test in understanding texture of pureed foods becomes clear from the fact that it is adopted by the Japanese

Society of Dysphagia Rehabilitation and an authorized method in the regulation of “Food for special dietary uses” issued by the Japanese Ministry of Consumers (2009) for characterization of mechanical properties of safe foods for dysphagia (Funami, 2011).

In the process of developing guidelines for dysphagia foods, the National Dysphagia Diet Task

Force analysed 100 foods for eight textural attributes of adhesiveness, cohesiveness, firmness, fracturability, hardness, springiness, viscosity and yield stress using a texture analyser, but the follow-up classification for texture-modified foods was qualitative and not clear (Mccullough,

Pelletier, & Steele, 2003). The characterisation of pureed foods with TPA has captured the wide diversity in texture. Differences in TPA parameters have been observed in various commercial pureed foods and pureed carrots formulated with different thickeners (Ettinger, 2012; Ilhamto,

2012; Wendin et al., 2010). Combining small deformation rheological measurement with large deformation texture profile analysis may be able to capture subtle changes in food structure leading to changes in textural attributes (Kealy, 2006).

2.4.3 Sensory properties of pureed foods

Sensory evaluation helps understand human perception about a particular product by evaluating its characteristics from the initial stages of touch and smell until the final stage of mastication. This is important in the development of new products, to assess the impact of varying ingredients and processing conditions on existing products, comparison ratings with similar competitive products, improve demand of existing products and gain an insight about what is/are the ‘critical parameters’ for liking / disliking a particular product. Sensory properties detail the human psychology part of food while giving an idea about the in-mouth processes associated with its acceptance or rejection

(Bourne, 2002). An insight into these properties can be achieved using various tests that are conducted based on the research objective. Sensory characterisation can be verbal or non-verbal and gives both qualitative and quantitative data depending on the test being conducted. The time, money and effort involved in this exercise vary from few hours to many days, depending on the purpose / objective of the test.

Classical Descriptive Analysis (DA) involves a panel of interested people proficient in describing and discriminating the required sensory attributes. A panel of 9-20 persons is trained for detecting small changes occurring during the mastication. The duration of training varies with product, the attribute being studied and complexity of food. The data obtained with this technique is detailed, robust and precise with focused information about specific attributes such as differences in smoothness of different yogurts (Varela & Ares, 2012). It assumes particular significance in specialty foods such as pureed foods which call for specific texture and where the desired consumers cannot be involved for reasons of safety and ethics. Panelists are trained for specific attributes. Training involves definition of attributes, deciding the intensity level on a reference

31 scale and method of evaluation. A trained panel acts like a well calibrated instrument giving consistent result as a group and with test replicates (Grygorczyk, 2012).

The disadvantage of a trained panel is that it does not capture the general consumer perspective

(Grygorczyk, 2012). In order to capture consumer language and understand their vocabulary of food descriptors, trained panel results are traditionally supplemented with consumer panel testing

(Giacalone, Ribeiro, & Frøst, 2013; Louw et al., 2013). Novel sensory profiling techniques, however, based on consumer perception are being increasingly used to capture the holistic view of a product. These sensory tests also known as rapid profile sensory techniques overcome the limitations of time and money involved in DA as the maximum time involved in rapid profiling is between 1 and 2 hours. These tests differ in methodology and output in the sense that it could be in the form of ranking or sorting the products, free choice description of products or choosing appropriate descriptors from the list provided (Reinbach, Giacalone, Ribeiro, Bredie, & Frøst,

2014). The choice of test depends on the kind of application or end-use. Napping® is a rapid sensory test which enables discrimination and sorting among a set of products based on similarities and differences, with emphasis on capturing individual perception (Perrin et al., 2008). It usually requires 12-15 individuals who are presented with all the products in one go which have to be placed on a A3 or A4 size paper (known as tablecloth or ‘‘nappe” in French language) in such a way that distance between products gives an idea about similarity and differences; the closer the products, the more similar they are perceived. Napping® is combined with Ultra Flash Profiling

(UFP) where after placing all the samples on the tablecloth, each product is characterised by few descriptors so as to give more information about it. The extensive list of attributes generated with this test can be used to decide the attributes which are considered important from consumer

32 perspective and quantitatively analysed using a trained panel. Although Napping® is fast and cost effective and DA is time and money intensive, the latter is an inevitable step for formulating correctly-textured foods, as it captures the subtle changes occurring in the mouth while chewing, mixing with saliva, preparing the bolus and pushing it in the pharynx. Sensory testing of pureed foods using hedonic scales or with individuals involved in the management of dysphagia might give an overall idea about the product but such tests lack the information related to minor textural intricacies during oral propulsive and pharyngeal stages of swallowing and required quantitative data for correlation with instrumental results (Seo, Hwang, Han, & Kim, 2007).

In the past, texture modifications in pureed foods with different thickeners or vitamins have been qualitatively evaluated for liking by dietitians or speech language pathologists (Houjaij et al., 2009;

Kennewell & Kokkinakos, 2007; Cassens, Johnson, & Keelan, 1996). A more detailed sensory characterisation helps in detailing the various attributes perceived during swallowing. Sensory characterisation with a trained panel helps in better understanding the attributes considered significant for dysphagia foods. This is also important to understand relations with instrumental measures which can be further utilised in generating desired end results.

Sensory characterisation of pureed foods meant for individuals with swallowing disorder is a comparatively recent thing (Ettinger & Duizer, 2014; Ilhamto, Keller, & Duizer, 2014; Wendin et al., 2010). Differences in firmness and chewing resistance were observed in commercial solid foods available for management of dysphagia (Wendin et al., 2010). A study by Ettinger & Duizer,

(2014) revealed that commercial pureed foods are significantly different in aroma, colour and perceived thickness. Small variations in liquid added during pureeing led to significant differences in perceived textural attributes of pureed turkey (Ilhamto et al., 2014). Different thickeners added

33 to pureed carrots change the appearance while also changing the textural attributes (Ilhamto et al.,

2014).

2.4.4 Correlation of Instrumental and Sensory evaluation

Instrumental measurements are conducted under controlled conditions such as temperature and shear rate while sensory evaluation measures in-mouth processes with no control of salivary secretion, shear rates and temperature (Grygorczyk, 2012). When behaviour of a food sample is tested instrumentally, temperature is controlled with various methods (like a water-bath) or varied systematically as required for the purpose of research. Shear-rates are also controlled and various flow-properties are obtained. Oral processing is a more complex process with a range of shear rates operating during oral manipulation which is also dependent on the type of food such as solid, semi-solid or liquid food and high- or low- viscous food. It is also dependent on the amount of salivary flow and various enzymes present in saliva which aid in food breakdown. In spite of these differences between instrumental measurements and sensory perception, often correlation analysis between these two types of measurements show how more controlled instrumental tests are related to perceived sensory properties of a food. Sensory testing can be expensive which make it less approachable in the commercial world. Strong correlations can help in predicting sensory behaviour which can be used in changing ingredients and processing conditions as per the requirements.

A comparison of TPA parameters and sensory properties in different therapeutic pureed cakes, showed that the most appropriate food for dysphagic individuals had minimal firmness and springiness, adequate cohesiveness and no adhesiveness (Houjaij et al., 2009). A positive relation was found between two sensory properties (firmness and chewing resistance) and instrumental

34 measures of storage modulus, maximum load and Young’s Modulus (Wendin et al., 2010). A study on thickened beverages, thin-honey and nectar categories, found positive relations between instrumental measures of viscosity and consistency coefficient with sensory perception of thickness, adhesiveness and stickiness (Damodhar, 2011). Back extrusion testing and sensory evaluation of in-house pureed foods highlighted the need for a balance between firmness and adhesiveness so as to have cohesive bolus with minimum slipperiness for safe swallow (Ilhamto,

2012). Minced and pureed peas had positive correlations between elastic and viscous moduli, yield stress and total solids to sensory perception of resistance to compression and time needed to swallow (Tobin, 2014). Total solids and viscous moduli had positive correlations with sensory cohesiveness and effort to form a bolus and negative correlation with moistness and ease of swallow (Tobin, 2014).

Based on high correlation between instrumental parameters and sensory evaluation, Truong et al.,

(1997), concluded that the former could be used for predicting texture of cooked sweetpotato. They found that shear stress (from Uniaxial Compression), fracturability, hardness and gumminess

(from TPA) significantly explain sensory textural attributes of cohesiveness, adhesiveness, hardness and moistness, in case of cooked sweetpotatoes from different cultivars. A study by

Loredo & Guerrero in (2011) predicted the sensory values of hardness, fracturability, adhesiveness, and cohesiveness based on a correlation model established between instrumental and sensory results using argentine foods as reference scale.

In the past studies have been done to increase diet and nutrition uptake of pureed foods by enhancing appearance, taste and various fortifications (Adolphe, Whiting, & Dahl, 2009;

Kennewell & Kokkinakos, 2007; Stahlman et al., 2001). It has been proven that wide differences exist in commercial pureed foods, both instrumental and sensory. This research on pureed carrot formulations using different hydrocolloids, aims to understand textural attributes required for safe swallow foods through a combination of structural, breakdown and sensory properties. This will help in understanding important parameters for developing quantitative standards for modified texture foods and enhance results of efforts directed to increase diet in people with swallowing disorder.

Chapter 3

3. TEXTURAL CHARACTERISATION OF PUREED FOODS WITH HYDROCOLLOIDS USING INSTRUMENTAL TECHNIQUES

3.1 INTRODUCTION

Pureed foods meant for dysphagia need to have specific textural properties in order to be safe for swallowing. These are intended to aid in oral manipulation of food and to contribute to a swallow- able bolus. This will minimize the risk of choking which commonly occurs with dysphagia.

Thickeners / hydrocolloids are often added to pureed foods for product stability and texture.

Thickeners/hydrocolloids are high molecular weight water soluble polysaccharides used for their thickening and water-binding ability. Also known as texture modifiers, hydrocolloids are added to foods to give desired textural properties with appropriate flow characteristics which include increased viscosity (thickening), water retention, firmness and smoothness (Hayakawa et al., 2014;

Funami, Ishihara, Nakauma, et al., 2012; Morris, Kirby, & Gunning, 1999). These are added to foods for a variety of applications such as fat-replacement, inhibition of ice crystal formation in frozen foods, stabilization in acidified dairy beverages and improvement of the quality and shelf- life of dough in bakery products (BahramParvar, Razavi, & Khodaparast, 2010; Bayarri, Chuliá,

& Costell, 2010; Fernández, Alvarez, & Canet, 2008; Gallardo-Escamilla, Kelly, & Delahunty,

2007; Downey, 2002). An in depth rheological characterization of hydrocolloid behaviour is of great use in being able to modulate texture as per the desired requirements for a food (Tárrega,

Martínez, Vélez- Ruiz, & Fiszman, 2014; Arancibia, Costell, & Bayarri, 2013; Fernández, Canet,

& Alvarez, 2009). Although hydrocolloids are used extensively in pureed foods, their impact on textural changes is still at infancy (Ilhamto, 2012).

Starch-based thickeners are the most common hydrocolloid used in commercial dysphagia foods and in preparation of in-house pureed foods in nursing homes (Cichero, 2013; Ilhamto, 2012;

Garcia, Chambers, Matta, & Clark, 2008; Dewar & Joyce, 2006). This may be because they are inexpensive ingredients, easily available, easily dispersed and hence, frequently used in food preparations. Native starch is modified to make it easily dispersible at varying temperatures.

Among the commercially available dysphagia thickeners, ThickenUp® (Nestlé HealthCare

Nutrition) has been used in many research studies (Leonard, White, McKenzie, & Belafsky, 2014;

O’Leary, Hanson, & Smith, 2010; Garcia et al., 2008). Some other starch thickeners specific for use in dysphagia are also available, one of which studied in this research is Unipure® D2560.

Xanthan is the most studied hydrocolloid in dysphagia diets next to starch. It has good water holding capacity, is not affected by external conditions such as temperature and pH and forms a rigid double helical structure at room temperature (Funami, Ishihara, & Nakauma, 2012).

Carrageenan and carboxymethyl cellulose are mainly used in milk-based products but are now finding applications in dysphagia foods (Hayakawa et al., 2014; Cichero, 2013; Tashiro,

Hasegawa, Kohyama, Kumagai, & Kumagai, 2010). Gellan has been used in commercial pureed foods and commonly used in Japan to study swallowing mechanisms (Hayakawa et al., 2014; Med-

Diet Inc., 2014; Funami, Ishihara, Nakauma, et al., 2012; Sheldon, 1999). Pectin is also being investigated for use in special foods (Damodhar, 2011; Tobin, 2014).

Texture is a function of food structure and its response to deformation (Stanley & Taylor, 1993).

These properties can be understood using a combination of rheological techniques, using large and small deformation tests, as they measure different properties of a food system (Fernandez et al.,

2006). Small deformation rheology measures properties of a product without destroying the

38 structure while large deformation tests capture breakdown properties that can be somewhat related to events occurring during mastication (Chen & Engelen, 2012). A combination of both types of tests, in conjunction with sensory testing is needed to better understand the structure, mechanical behaviour and in-mouth perception of a food matrix (Guo, Ye, Lad, Dalgleish, & Singh, 2013;

Kealy, 2006).

Rheological measurements have been used to understand the behaviour of hydrocolloids in a number of thickened pureed food matrices such as commercial baby pureed foods, pureed sweet potatoes, fresh / frozen pureed vegetables with cryoprotectants, and pureed and mashed potatoes with single / mixed hydrocolloids (Álvarez, Fernández, Olivares, Jiménez, & Canet, 2013;

Alvarez, Jiménez, Olivares, Barrios, & Canet, 2012; Fernández et al., 2008; Ahmed &

Ramaswamy, 2007; Downey, 2002; Truong & Walter, 1994). Similar studies on dysphagia- specific thickened beverages have shown differences in the final product based on type of thickener such as starch or gum, type of product such as pre-thickened or thickened at time of serving with instant food thickeners, serving temperature, beverage used in the sample and time gap between preparation and consumption of fluid (Garcia et al., 2008; Adeleye & Rachal, 2007; Dewar &

Joyce, 2006). However, to date, no such studies have been conducted on pureed foods for older adults with swallowing disorders. Analysis of the rheological and mechanical behaviour of hydrocolloid gels have been studied from a ‘safe-swallow’ perspective for dysphagia but the impact of hydrocolloid addition to pureed food matrices is still at a conceptual stage although of great importance because of the implications for the development of products for the health care industry (Rao, 2013; Funami, Ishihara, Nakauma, et al., 2012; Ishihara, Nakauma, Funami, Odake,

& Nishinari, 2011a; Nakauma et al., 2011).

The objective of this research was to understand the impact of different hydrocolloids on the textural properties of a pureed food matrix. Differences in textures were measured to get an insight of changes occurring to the samples, using both small and large deformation tests. At the present time, viscosity is the parameter considered to be important in the design of pureed food. In this work, various matrices were prepared with a similar value of viscosity, to examine how matrices containing different hydrocolloids but having similar viscosity could differ in other rheological properties that may be relevant to the quality of product for dysphagia.

3.2 MATERIALS AND METHODS

3.2.1 Materials

Carrots were purchased from local supermarkets (Guelph, Ontario) and the hydrocolloids were kindly donated for use in the formulation of pureed carrots. Gellan gum (Kelcogel LT100), and xanthan gum (KELTROL®–521) were obtained from CP Kelco (Atlanta, GA, USA). Pectin

(GENU BETA, CP Kelco, Lille Skensved, Denmark), and carboxymethyl cellulose - CMC

(CEKOL®50000P, CP Kelco, Äänekoski, Finland) were also used. Carrageenan (GPI006) was obtained from GPI, New Market, Ontario, Canada. Two commercially dysphagia-specific proprietary thickeners – a modified corn starch – Uni-Pure® D2560 abbreviated as MCS (i) and a starch-gum blend Uni-Pure® Dys-sperse abbreviated as Unipure were supplied by Ingredion Inc.

(Bridgewater, New Jersey, USA). Thicken Up® (Nestle Health Science) specifically designed for thickening, was store bought and used as reference. In addition, a commercial carrot puree product

(Puree Essential Carrot - PE#21734) was sourced from Marsan Foods, Toronto, Canada and included as a basis for comparison.

3.2.2 Sample Preparation

To prepare purees, peeled and sliced carrots were cooked in a steamer for 30 min and then pureed at 1750 rpm using a kitchen mixer (Kitchen Aid Food Chopper KFC3511). The hydrocolloids were added while pureeing (3-5 min) so as to achieve maximum solubility during shearing, at a temperature between 40 - 45°C. Under these conditions, the hydrocolloids would be able to be well dispersed and hydrated. Samples were prepared 24 h before testing, refrigerated (5°C) and either warmed in a water-bath on the day of testing to achieve the desired temperature (55°C) for rheological measurements or left on counter top to achieve room temperature for texture profile analysis (TPA) using Texture Analyser.

3.2.3 Viscosity Measurement

All purees were formulated to obtain a value of viscosity similar to that of ThickenUp® used as reference sample. This was done by matching the apparent viscosity for each hydrocolloid, calculated as an average of values in the shear rate range of 41-50 s-1, to that of the reference.

Viscosity was measured using an Advanced Rheometer AR 1000 with Rheology Advantage

Instrument Control AR software v5.4.0 (TA Instruments Ltd., New Castle, DW, USA) with a 40 mm serrated plate geometry at a gap of 3 mm, by applying a continuous shear rate ramp from 1 –

150 sˉ1 at 55°C. This is the serving temperature of pureed foods in Long-term Care Center.

Temperature was maintained with an external water bath. All tests were carried out in triplicate.

The concentration of each hydrocolloid finalised after matching to the mean (± standard deviation) viscosity values of control at shear rate 41-50 s-1 is as shown in Table 3.1. Apparent viscosity values at shear rates of 10 s-1, 50 s-1 and 100 s-1 were selected for comparison among samples.

Table 3.1 - Concentration of each hydrocolloid matched with viscosity values of ThickenUp® at shear rate 41-50 s-1. Values are the average of three independent experiments.

Viscosity (Pa s) Hydrocolloid Concentration (% w/w) Mean±SD

ThickenUp® 1.6 3.3±0.5

MCS(i) 2.0 3.6±0.4

Unipure 5.0 3.2±0.3

Xanthan 1.2 3.5±0.3

Pectin 0.8 3.6±0.4

CMC 0.5 3.4±0.6

Gellan 0.4 3.4±0.2

Carrageenan 0.8 2.7±0.6

3.2.4 Rheological Properties

Viscoelastic measurements were conducted in a Paar Physica MCR 301 rheometer (Anton Paar

Germany GmbH, Ostfildern, Germany) with a measuring cell (P-PTD 120) equipped with a peltier temperature controller. A Julabo circulator (JulaboWest, Inc., CA, USA) was used as a counter

42 cooling system for the peltier element. A serrated plate geometry (PP50/P2) was used at a 3 mm gap. Small Amplitude Oscillatory Shear (SAOS) tests included a strain sweep, a shear stress sweep and frequency sweep. Linear Viscoelastic Region (LVR) was determined by conducting an amplitude sweep ranging from 0.01% to 100% strain at a frequency of 1 Hz. The mechanical spectra were performed from 100-0.1 Hz at 0.1% strain. Viscoelastic parameters of storage modulus (G´), loss modulus (G´´), complex modulus (G*), complex viscosity (*) and phase angle

(δ) at 1 Hz and frequency slopes were analysed for comparing the different pureed carrot formulations. A continuous shear stress ramp test was conducted from 1-300 Pa at a frequency of

1 Hz to determine the yield and flow point. The yield point was considered as the limiting shear stress value of LVR range. The crossover point, G´ = G´´ in this case was taken as the flow point.

Yield point gives an idea about structure strength, where the bonds starts to rupture whereas flow point gives information related to breaking of internal structure resulting in final flow (Mezger,

2006). All the tests were conducted in duplicate at 55°C and a peltier hood (H-PTD 200) was used for uniform temperature control.

3.2.5 Mechanical Properties

Texture Profile Analysis was done using a TA.XT plus Texture Analyser (Stable Micro Systems

Ltd, Godalming, Surrey, UK). Pureed carrot sample (weight 50±1 g) was loaded in a 40 mm diameter beaker and tapped to level the surface. On the testing day, samples were taken out of refrigerator and held at room temperature (~20ºC). Test settings included penetrating the sample with a 2.54 cm crosshead acrylic cylindrical probe at a speed of 180 mm min-1 up to a strain level of 33.3%. A two bite compression was performed and all measures were made in triplicate for each sample. Data was collected using Exponent software (Stable Micro Systems Ltd, Godalming,

Surrey, UK). Exponent Stable Micro Systems software was used to extract data from the TPA curve for primary and secondary parameters which included hardness, adhesiveness, cohesiveness, springiness, gumminess and chewiness (Canet, Alvarez, Fernandez, & Tortosa, 2005; Bourne,

2002; Rosenthal, 1999).

3.3 DATA ANALYSIS

Institute, Cary, NC). Two-way ANOVA was conducted to see if significant differences existed in measured parameters (p < 0.05) and replicates of testing. A Tukey’s Honest Significant Difference

(HSD) test was conducted to identify differences among samples for each significant measurement.

3.4 RESULTS AND DISCUSSION

3.4.1 Viscosity

All the samples exhibited a shear thinning behaviour, with the viscosity decreasing steeply with increasing shear rate (Figure 3.1). Table 3.2 summarizes the variation in viscosity at selected shear rates for pureed carrot formulations with different hydrocolloids. When looking at viscosities measured at different shear rates, differences were observed among samples at low shear (10 s-1).

Commercial puree had a high apparent viscosity (27.5 Pa s), while the carrot puree containing

CMC showed the lowest value at 12.1 Pa s. The values of viscosity for all prepared samples were not significantly different at 50 s-1 and 100 s-1. This has been shown before also for commercial thickened beverages, suggesting that, although viscosity at the critical shear rate (50 s-1) was similar, the samples had different rheological properties (for example, a different low shear

44 viscosity or complex modulus) (Payne et al. 2011). These differences may be critical to the sensory attributes of the products.

100

10 Viscosity (Pa.s) Viscosity 1

0 1 10 100 1000 Shear Rate (s‾ˡ)

ThickenUp® MCS(i) Unipure Xanthan Pectin CMC Gellan Carrageenan Commercial

Figure 3.1 - Shear thinning behaviour of pureed carrot formulations with different hydrocolloids. Apparent viscosity was measured with shear rate ramp from 1 – 150 s-1 in 8 min at 55ºC. Graph shows representative runs of one of the three replicates

Table 3.2 - Apparent viscosity measured at three shear rates (10, 50 and 100 s-1) measured at 55°C for pureed carrot formulations with different hydrocolloids. Values are the average of three separate experiments, and means with different letters within same column indicate significant difference (p<0.05).

Viscosity @ 10s-1 Viscosity @ 50s-1 Viscosity @ 100s-1 Sample (Pa s) (Pa s) (Pa s)

Mean ± SD Mean ± SD Mean ± SD

ThickenUp® 16.3±2.7bcde 3.0±0.4a 1.5±0.2a

MCS(i) 19.4±2.3bcd 3.2±0.3a 1.6±0.2a

Unipure 13.1±0.7de 2.9±0.2a 1.6±0.1a

Xanthan 14.2±3.1cde 3.2±0.2a 1.6±0.1a

Pectin 14.6±1.3cde 3.3±0.3a 1.8±0.2a

CMC 12.1±2.4e 2.1±1.2a 2.2±1.2a

Gellan 20.6±2.5abc 2.5±0.5a 1.1±0.2a

Carrageenan 21.8±1.7ab 2.4±0.6a 1.1±0.2a

Commercial 27.5±3.5a 3.8±0.9a 1.8±0.4a

3.4.2 Small Deformation Tests

Pureed carrot formulations were evaluated for viscoelastic properties by carrying out three tests: a

Strain Sweep, a Stress Sweep and a Frequency Sweep.

3.4.2.1 Strain Sweep

A strain sweep was performed for all samples to determine the limits of the linear viscoelastic region (LVR) (Figure 3.2). Table 3.3 summarizes the values of the elastic modulus measured in the LVR and the values of critical strain defining the LVR. All samples did not show a significant difference in terms of critical strain for the linear viscoelastic region (Table 3.3). In all cases, the deformation range, in terms of strain rate at LVR, indicates the point at which the material no longer shows a linear viscoelastic behaviour, and it may be associated to the brittleness of the molecular interactions within the material (Grygorczyk, 2012; van Vliet, 2002). It is also considered as an index of material stability and extensibility (Campo-Deaño, Tovar, Jesús, Teresa,

& Javier, 2009). Results for maximum strain at LVR indicate that all hydrocolloids behaved similarly in pureed carrot sample for extensibility of bonds. Albeit there was no difference in the

LVR range for all samples, with about 0.1% strain considered the limit for the LVR, the values of

G´ were different between the different carrot puree samples.

The value of G´ indicates the stiffness of the material at rest (Mezger & Stellrecht, 2000). As observed in Table 3.3, carrot puree with pectin and carrageenan showed high G´ values compared to the rest of the samples, which were all statistically comparable in G´ values to the reference samples containing ThickenUp® and the commercial carrot puree. It was concluded that the stiffness and the strength of the molecular interactions was much higher for carrot puree containing

47 pectin and carrageenan. Pureed carrot samples prepared with Unipure demonstrated the least stiff structure with a low G´.

Table 3.3 - Average of parameters obtained by strain sweep (0.1 – 100 % strain at 1 Hz, 55ºC) of pureed carrot formulations using different hydrocolloids, at various concentrations having similar viscosity at 50 s-1. Results are means of two separate experiments. Means with the same letters within a column are not significantly different (p<0.05).

Strain @ LVR (%) G´LVR (Pa) Sample Mean±SD Mean±SD

ThickenUp® 0.38±0.15a 3904±1500bc

MCS(i) 0.65±0.30a 4169±565bc

Unipure 0.50±0.16a 2002±954c

Xanthan 0.78±0.42a 3561±271bc

Pectin 0.70±0.33a 7070±2062ab

CMC 0.28±0.01a 2725±1091bc

Gellan 0.43±0.01a 4456±510abc

Carrageenan 0.65±0.30a 9313±1601a

Commercial 0.37±0.09a 3454±76bc

Behaviour of samples in the non-linear viscoelastic region provides more detailed rheological information and hence should be included for characterising food material properties and quality attributes (Alvarez, Fernández, Solas, & Canet, 2011; Gunasekaran & Ak, 2000). The changes in the elastic and viscous modulus for the various hydrocolloids as a function of increasing strain are shown in Figure 3.2. The elastic modulus decreased with increase in strain after LVR for all samples. Viscous modulus initially increased in the non-linear viscoelastic region followed by its decline with further increase in strain with the exception of carrot purees containing Unipure and

CMC.

Based on the classification of gel behaviour in the non-linear region, carrot purees containing

Unipure and CMC showed a strain thinning behaviour when looking at the changes in the viscous modulus as a function of strain. All the other hydrocolloids instead showed a weak strain-overshoot

(Hyun, Kim, Ahn, & Lee, 2002). This latter behaviour has been earlier reported for xanthan gum solutions (Carmona, Ramírez, Calero, García, & Muñoz, 2014; Song, Kuk, & Chang, 2006). In case of strain thinning, the network structure is lost easily, with no chance of recovery while in case of weak strain-overshoot, with a slight increase in strain bonds are realigned and the system tries to maintain network structure, resisting against deformation, which is destroyed and finally starts to flow at higher deformations (Hyun et al., 2011; Sim, Ahn, & Lee, 2003).

The differences in the rheological behaviour at higher strain may be of great relevance in the development of products for dysphagic patients. In these products, emphasis is focused on ease of swallow, formulations with gum and starch or other such formulations should be tried which are strain thinning and hence flow easily with increasing strains.

10000 A

1000 Elastic Modulus G' (Pa) G' ElasticModulus

100 0.01 0.1 1 10 100 Strain (%)

10000 B

1000 Viscous Modulus G" (Pa) G" Modulus Viscous

100 0.01 0.1 1 10 100 Strain (%)

ThickenUp® MCS(i) Unipure Xanthan Pectin CMC Gellan Carrageenan Commercial

Figure 3.2 - Variations of elastic (A) and viscous modulus (B) as a function of strain for mixtures of pureed carrots containing different hydrocolloids, at various concentrations to obtain a viscosity at 50 s-1 of about 3 Pa s. Curves are representative runs of one of the two replicates.

3.4.2.2 Stress Sweep

Yield point and flow point values for each sample are shown in Table 3.4. Carrot puree containing carrageenan showed a significantly higher yield point than MCS (i), xanthan, pectin and CMC.

Samples containing MCS (i), xanthan, pectin and CMC showed the lowest values of yield point.

The flow point was similar for all pureed carrot samples except for significant differences between purees containing MCS (i) and pectin. Carrot purees made with MCS (i) had a higher flow point

(191.7 Pa) compared to pectin (82.4 Pa). The rest of the hydrocolloids behaved similar to the reference sample and the commercial sample. The limiting shear stress value of the LVE region in the stress sweep was taken as the yield point and the cross over point of G´ - G´´ was taken as the flow point (Mezger, 2006). Yield point indicates the threshold force needed for the onset of structural breakdown. After breaching small oscillatory deformation, further application of force will cause continuous disruption of network structure and the point where the material does not revert to its elastic component and only flows with G´´ > G´, indicates the flow point (Mezger,

2006). It indicates the transition from solid to liquid-like behaviour.

Results from Table 3.4 indicate that MCS (i) with a low yield point requires less force for initiating gel rupture but more force is needed to make it start flowing because of its high flow point. Carrot puree containing pectin with very low flow point indicated least amount of stress for changing from a solid to a liquid-like behaviour.

Table 3.4 - Results of stress sweep 1 – 300 Pa at 55ºC for mixtures of pureed carrots containing different hydrocolloids, at various concentrations to obtain a viscosity at 50 s-1 of about 3 Pa s. Means are the average of two separate experiments, and different letters within same column indicate significant differences (p<0.05).

Yield Point (Pa) Flow Point (Pa) Sample Mean±SD Mean±SD

ThickenUp® 12.0±3.8ab 113±19ab

MCS(i) 8.9±0.6b 192±52a

Unipure 11.6±0.01ab 133±11ab

Xanthan 8.3±0.7b 159±4ab

Pectin 9.0±0.42b 82±3b

CMC 8.9±0.4b 114±18ab

Gellan 11.3±0.01ab 162±48ab

Carrageenan 16.7±3.43a 147±11ab

Commercial 10.2±0.1ab 136±0.1ab

3.4.2.3 Frequency Sweep

The frequency sweep results shown in Figure 3.3 indicate that all samples had weak-gel characteristics where the elastic modulus (G´) was higher than viscous modulus (G´´) over the entire range and much less variation with frequency. All pureed carrot formulations had G´´ lower than G´ by one order of magnitude. This magnitude of difference is a criterion suggested for safely swallowed foods (Ishihara et al., 2011a).

The frequency dependence of G´ is used to understand the nature of gel interaction. A higher slope value indicates more variation with frequency leading to weak structure while a strong cross-linked gel has a lower slope value against frequency (Gunasekaran & Ak, 2000; Tunick, 2011). The slope values for G´ and G* (complex modulus) are shown in Table 3.5. These values suggest that all the samples have strong molecular interactions, except for the purees containing CMC which showed a higher slope for both G´ and G*. Table 3.5 also summarizes the values of the slope for complex viscosity (ɳ*). Complex viscosity has been often employed in oral processing studies (Kealy, 2006;

Tunick, 2000). Slope of complex viscosity might represent the composite flow behaviour

(considering both elastic and viscous properties) of food during oral processing. All samples, independently of the hydrocolloid used, had a similar slope of complex viscosity.

100000

10000

1000 Elastic Modulus G' (Pa) G' ElasticModulus

100 0.1 1 10 100 Frequency (Hz)

10000 B

1000 Viscous Modulus G" (Pa) G" Modulus Viscous

100 0.1 1 10 100 Frequency (Hz) ThickenUp® MCS(i) Unipure Xanthan Pectin CMC Gellan Carrageenan Commercial Figure 3.3 - Variations of elastic (A) and viscous modulus (B) as a function of frequency for mixtures of pureed carrots containing different hydrocolloids, at various concentrations to obtain a viscosity at 50 s-1 of about 3 Pa s. Curves are representative runs of two replicate experiments.

Table 3.5 - Log-Log slope of viscoelastic parameters against frequency as obtained from frequency sweep for mixtures of pureed carrots containing different hydrocolloids, at various concentrations to obtain a viscosity at 50 s-1 of about 3 Pa s. Results are the mean of two separate experiments, and different letters within same column indicate statistically significant differences (p<0.05).

Slope G´ Slope G* Slope ɳ* Sample Mean±SD Mean±SD Mean±SD

ThickenUp® 0.101±0.012b 0.100±0.007b -0.91±0.50a

MCS(i) 0.097±0.015b 0.101±0.009b -0.92±0.06a

Unipure 0.093±0.004b 0.092±0.002b -0.93±0.01a

Xanthan 0.101±0.002b 0.096±0.006b -0.93±0.03a

Pectin 0.103±0.002b 0.106±0.001b -0.90±0.02a

CMC 0.140±0.008a 0.141±0.012a -0.86±0.03a

Gellan 0.094±0.001b 0.098±0.001b -0.92±0.01a

Carrageenan 0.104±0.007b 0.106±0.009b -0.90±0.01a

Commercial 0.085±0.001b 0.091±0.001b -0.93±0.01a

Dynamic viscoelastic properties of elastic modulus, viscous modulus, complex modulus (G*), complex viscosity (ɳ*) and phase angle (δ) of hydrocolloids were compared at 1 Hz, and the results are summarized in Figure 3.4 and Table 3.6. The ANOVA results for rheological parameters are in Appendix A. There were no significant differences among samples for G´ (Figure 3.4). The viscous component G´´, varied significantly which led to differences in G* and ɳ* across samples

(Table 3.6). Complex modulus (G*) which accounts for both the elastic and viscous component is often used to characterize gel structures (Payne et al., 2011). It is used as an indicator of gel stiffness, shape retention and resistance against deformation (Haghighi, Rezaei, Labbafi, &

Khodaiyan, 2011; Gunasekaran & Ak, 2000). Complex viscosity is the ratio of G* to frequency and indicates the resistance to flow (Tunick, 2011). The results for G* and ɳ* were similar across all samples. Carrageenan and pectin had the highest values of G* and ɳ*, as already shown for the

G´ data of strain sweep (Table 3.3). The carrot puree containing Unipure showed the lowest value of G* and ɳ*. Hence, in spite of all the samples having a similar value of apparent viscosity at 50 s-1, the puree containing Unipure had a weaker gel structure with less resistance to deformation and flow, while samples containing carrageenan and pectin had stiffer structure.

Table 3.6 also summarizes the values of the phase angle (δ). This parameter is a measure of degree of viscoelasticity of a material (Mukisa et al., 2012). In this study, phase angle ranged from 7° to

15° for all samples, highlighting the gel nature of the carrot purees. A lower δ represents more elastic response of a material to external stress (Foegeding, Vardhanabhuti, & Yang, 2011). When comparing all the carrot purees, it was clear that samples containing CMC showed a significantly higher phase angle (14.2º) compared to samples containing other hydrocolloids and the commercial carrot puree had the lowest value of phase angle (7.9). CMC with a higher phase angle,

56 higher slope values of G´ and G* and low G´ in the strain sweep and lower G* and ɳ* indicated its weaker structure compared to other hydrocolloids. The higher value for δ of carrot purees containing Unipure, coupled with low values for G* and ɳ* may suggest to be easier to swallow compared to the other samples, especially those containing pectin or carrageenan. It is also interesting to observe that Unipure and CMC were the two hydrocolloids with strain thinning behaviour of viscous modulus in the non-linear region of strain sweep.

a 14000 13000 a 12000 11000 10000 a 9000 8000 7000 a 6000 a a 5000 4000 a a a a Elastic Modulus (Pa) ElasticModulus 3000 2000 1000 0

b 3000

2000 a ab

ab ab b 1000 ab b

b b Viscous Modulus (Pa) Modulus Viscous

Figure 3.4 - Average values of two replicates for (a) elastic modulus - G´ and (b) viscous modulus - G´´ for mixtures of pureed carrots containing different hydrocolloids, at various concentrations to obtain a viscosity at 50 s-1 of about 3 Pa s. Different letters denote significant differences at p<0.05.

Table 3.6 - Viscoelastic parameters at 1 Hz obtained from frequency sweep (0.1 – 100 Hz at 0.1% strain) at 55 ºC for mixtures of pureed carrots containing different hydrocolloids, at various concentrations to obtain a viscosity at 50 s-1 of about 3 Pa s. Values are the average of two independent experiments, and within a column, different letters indicate statistical significant differences (p<0.05).

G* (Pa) η* (Pa s) Phase Angle (°) Sample Mean±SD Mean±SD Mean±SD

ThickenUp® 3975±1562bc 632±250bc 9.9±0.6c

MCS(i) 4435±714bc 706±114bc 10.2±0.3c

Unipure 1744±1054c 277±168c 12.1±1.1b

Xanthan 3325±219bc 529±34bc 10.8±0.1bc

Pectin 7225±2086ab 1148±328ab 10.1±0.1c

bc CMC 2525±1096bc 402±174 14.2±0.1a

Gellan 4680±297bc 745±47bc 9.4±0.2cd

Carrageenan 9890±1570a 1575±248a 9.6±0.3cd

Commercial 3510±57bc 558±9bc 7.9±0.1d

3.4.3 Texture Profile Analysis (TPA)

TPA mimics the human mastication behaviour and is performed as a two-bite compression test. It is an important imitative test for textural characterisation as it provides a link between mechanical properties and textural attributes during oral processing (Chen, 2009). A force – time curve gives the output in the form of various parameters as listed in Table 3.7.

The force required to compress the sample during the first bite is represented as hardness.

Carrageenan, gellan and MCS (i) were significantly higher in hardness compared to CMC. Higher values of hardness have been earlier reported for carrageenan and gellan blended with rice starch.

This hardness was attributed to the network structure imparted by the presence of these polysaccharide chains within the matrix (Huang, Kennedy, Li, Xu, & Xie, 2007). After the first bite work needed to overcome the attractive forces between sample and the instrumental probe is denoted as adhesiveness (Tunick, 2000). The two modified corn starches, MCS (i) and

ThickenUp®, had the highest values for adhesiveness while gellan with a score of 45 g.sec was low in adhesiveness. Unipure and carrageenan were similar in adhesiveness. After the deformation of sample in the first bite, the extent or rate at which it returns to its original shape is measured as springiness. There were no significant differences among hydrocolloids for springiness.

In a study comparing four commercial cream cheeses, Kealy (2006) found that springiness and G´ values agreed reasonably well, except that the magnitude of measurements was in general opposite.

In the present research, a similar trend has been observed where the pureed carrot formulations were not significantly different in terms of springiness and G´ (Figure 3.4a and Table 3.7).

Cohesiveness measures the structural strength of food’s internal bonds, which holds it together in a bolus and prevents from disintegrating into fragments during swallowing.

Table 3.7 - Results of Texture Profile Analysis (TPA) using TA.XT plus Texture Analyser for pureed carrots using different hydrocolloids. Mean is the average of three independent experiments, and different letters within same column indicate significant differences (p<0.05).

Hardness(g) Adhesiveness (g.sec) Springiness Cohesiveness Gumminess (g) Samples Mean±SD Mean±SD Mean±SD Mean±SD Mean±SD

ThickenUp® 81±5bcde 195±9f 0.90±0.01a 0.80±0.0ab 64±4bc

MCS(i) 95±5bc 197±6f 0.90±0.01a 0.80±0.03ab 77±2b

Unipure 60±10cde 80±6c 1.00±0.01a 0.70±0.04bc 45±5c

Xanthan 61±3cde 120±15de 1.00±0.01a 0.70±0.02bc 45±2c

Pectin 59±4de 139±10e 1.00±0.01a 0.80±0.01ab 47±3c

CMC 48±3e 96±11cd 1.00±0.01a 0.90±0.04a 41±1c

Gellan 94±8bcd 45±12b 1.00±0.03a 0.70±0.06c 64±7bc

Carrageenan 112±21b 78±13c 1.00±0.01a 0.70±0.01bc 83±16b

Commercial 273±23a 11±1.3a 0.90±0.15a 0.50±0.03d 135±19a

Samples with CMC, MCS (i), ThickenUp® and pectin showed higher cohesiveness compared to pureed carrot samples made with other tested hydrocolloids. The commercial carrot puree had the lowest value for cohesiveness. Gumminess was also measured, as an indication of the amount of work needed to be done so as to make a food sample ready for swallow. Carrot puree containing carrageenan and MCS (i) had significantly higher values for gumminess compared to Unipure, xanthan, pectin and CMC. The commercial sample had the highest value for gumminess.

Although the commercial sample had similarities with other hydrocolloids in rheological measurements, TPA clearly demarcated the commercial sample from the rest of the hydrocolloids tested in pureed carrot formulations with a high hardness (273 g) and gumminess (135 g) and low adhesiveness (11g.sec) and cohesiveness (0.50).

3.4.4 Discussion

Carrot purees made with different hydrocolloids so as to have similar values of apparent viscosity at 50 s-1, exhibited subtle differences across most of the instrumental parameters. All hydrocolloids had similar values for deformation range in the form of length of LVR (% strain), G´ (frequency sweep) and springiness (TPA), all of which can probably be related to extensibility of bonds.

Hydrocolloids also exhibited similarities in slope of ɳ* which represents viscoelastic oral flow properties. Despite no clear demarcation showing one hydrocolloid behaving differently to the others during small and large deformation tests some subtle differences existed between different

-1 pureed carrot formulations. Carrageenan with a higher viscosity at 10 s , G´LVR, G*, ɳ*, yield point, hardness and gumminess and lower values for phase angle and cohesiveness had a strong gel-structure which would need more energy for initiating structural breakdown but would disrupt

62 and fragment into pieces easily once the bonds are broken. Pectin shared similarities with carrageenan under small deformation conditions but exhibited very different characteristics when subjected to large deformation conditions. It had a stiff structure at rest and under small deformation but behaved quite opposite in case of large deformation tests. It had a low yield and flow point, low hardness, higher cohesiveness with lower energy needed to make a swallow-able bolus. CMC displayed a weak gel-structure having low viscosity at 10 s-1, lower G´ at LVR, yield point, G* and ɳ*and higher values for phase angle and slope of G´ and G*. It had the highest cohesiveness accompanied by lower values for gumminess which indicated that carrot purees containing CMC was easier to make a swallow-able bolus. Unipure had a low viscosity at 10 s-1, lower G´LVR, G*, ɳ*, hardness and gumminess and higher phase angle values with strain-thinning behaviour. MCS (i) had a lower yield point and higher values for flow point, hardness, adhesiveness, cohesiveness and gumminess. An interesting observation was that while the reference sample and the commercial sample had similarities for rheological measurements

(except for phase angle) they had different results for TPA. This highlights the fact that combination of small and large deformation tests using rheology and TPA is necessary for textural characterisation of pureed foods.

Different criteria have been considered important while designing the diet for people with swallowing difficulties. These include yield stress (dysphagia fluids), yield strain, G´, G´´, balance of viscoelasticity, adhesiveness and cohesiveness (Tobin, 2014; Ishihara et al., 2011a; Loret et al.,

2011; Nakauma et al., 2011; Peyron et al., 2011; Wendin et al., 2010). Few studies have examined the relation between these rheological measures and swallowing of a pureed food matrix.

3.5 CONCLUSIONS

The objective of this research was to characterise pureed carrot formulations with different hydrocolloids having similar apparent viscosities in the shear rate range of 41–50 s-1. Textural characterisation of pureed carrot formulations using large and small deformation tests revealed subtle differences between hydrocolloids. All the hydrocolloids behaved similarly for brittleness, elastic component, springiness and slope of complex viscosity. Few hydrocolloids such as carrageenan, pectin, CMC, Unipure and MCS (i) showed distinct characteristics compared to the reference sample under certain testing conditions. Xanthan and gellan had similarities with reference sample for all rheological measurements and most of the TPA measurements. A correlation of these instrumental parameters with sensory will give a clear understanding of textural attributes which are important for dysphagia. Also understanding and comparison of behaviour of hydrocolloids under instrumental testing and sensory testing is necessary for more detailed insight of textural characteristics of pureed foods.

Chapter 4

4. TEXTURAL CHARACTERISATION OF PUREED CARROTS WITH HYDROCOLLOIDS USING SENSORY TECHNIQUES OF NAPPING® AND DESCRIPTIVE ANALYSIS

4.1 INTRODUCTION

Eating food is normally a pleasurable experience. However, in some cases this is a high risk activity which leads to choking. This is particularly prevalent in people with swallowing difficulties. For instance, individuals with pharyngeal swallowing dysfunction have difficulties in oral manipulation of food and so modified texture foods are part of compensation strategy used to maintain their regular diet. This usually results in loss of appetite and proper nutrition.

Pureed foods, a class of modified texture foods, have to be prepared with great deal of caution.

Providing the “right” texture is the underlying concern as inappropriate textures can lead to other complications such as choking and even death in some cases (Jukes et al., 2012; Berzlanovich et al., 2005). The “right” texture is one that is easy to manipulate and swallow. To acquire this, the texture of the food must be modified. This process of modification destroys the original texture and in doing so, results in a food that is often unidentifiable. This reduces the desire to eat and leading to a decrease in food intake (Keller & Duizer, 2014b). Although individuals understand that pureed foods are their regular dietary intake, it is never their first choice (Keller & Duizer,

2014b). Consumption of these foods creates a psychological burden in individuals due to its poor appearance and texture. Hence greater attention need to be paid to the sensory aspects of pureed foods (Tobin, 2014).

One negative aspect of pureed food is its appearance, however, changes using 3-dimensional molds to shape the food has been shown to increase food intake (Lepore, Sims, Gal, & Dahl, 2014;

Cassens et al., 1996). New techniques such as molecular gastronomy and 3-D printing are now being investigated for making pureed foods. An important consideration for success of these efforts is proper sensory textural characterisation. Addition of hydrocolloids is a pre-requisite in all these techniques used for enhancing the appeal of pureed foods. Altering the type of hydrocolloid used in a puree in order to obtain the desired instrumental characterisation invariably leads to changes in sensory properties such as appearance, flavour and mouthfeel (Soukoulis &

Tzia, 2008). This is the main reason for an increasing number of studies focussing on understanding changes in sensory attributes during product development (Soukoulis, Lyroni, &

Tzia, 2010; Janhøj, Bom Frøst, & Ipsen, 2008; Gallardo-Escamilla et al., 2007).For instance, gum- based thickeners impart slickness while starch-based thickeners impart grainy texture and starchy flavour to thickened beverages (Matta, Chambers, Garcia, & Helverson, 2006). Risk of aspiration changes with the type of thickener used, so selection of thickener and appropriate texture is critical in the dysphagia diet (Leonard et al., 2014). Proper sensory texture characterisation with profiling of appearance and flavour can help in designing desirable safe-to-swallow foods.

Sensory profiling can be done by various techniques such as the traditional technique of

Descriptive Analysis (DA) / Conventional Profiling (CP) and / or novel techniques of rapid profiling methods. The latter is increasingly being used to overcome the limitations of time and money involved with the former technique. Also the novel methods are envisaged to better capture and understand consumer perception compared to DA which uses trained panel who focus on selected attributes. In spite of these shortcomings, DA is a pre-requisite in initial stages of

66 understanding textural oral perception of pureed foods. DA provides quantitative data which can be compared with instrumental measurements to help formulate safe foods combined with good sensory appeal. According to Albert et al (2011), DA provides more robust data from statistical point of view and should be used where small and subtle differences exist across samples. In chapter 3, instrumental characterisation of pureed carrot formulations made with different hydrocolloids confirmed minor textural differences, making DA an appropriate choice of test. For mapping of complex products, Napping®, a rapid sensory technique, has been suggested as a quick tool to capture consumer perception and for direct feedback from consumers (Albert et al., 2011).

Napping by modality, known as partial napping (PN), performed with untrained panelists, unfamiliar with a product, is a viable method to be employed for selecting specific descriptors for speciality foods to be used subsequently in DA (Giacalone et al., 2013; Louw et al., 2013; Albert et al., 2011). So in this research, DA was used for textural characterisation based on the set of attributes selected after Napping®. The Napping® approach selected was partial napping for appearance, flavour and texture individually in order to understand the effect of different hydrocolloids on these sensory modalities.

4.2 MATERIALS & METHOD

4.2.1 Samples

Pureed carrot samples were prepared with eight hydrocolloids as described in Chapter 3. In order to maintain consistency in instrumental and sensory testing, samples were prepared one day before sensory testing and refrigerated (5°C). The previously frozen commercial sample was kept in the refrigerator for 24 hours before sensory evaluation, for thawing. On the testing day, all samples were scooped into Styrofoam cups with a No.2 scoop (weight of 24 ± 2 g), warmed and maintained

67 at 55 °C before serving for evaluation. Three digit blinding codes were used as identifiers for the samples to avoid any bias during testing. Crackers and water were provided to cleanse the palate after testing each sample.

4.2.2 Sensory Evaluation

4.2.2.1 Napping®

Rapid profiling using partial napping (PN) was conducted in two trials. The first trial was with11 judges and the second was with 13. Individuals taking part in the profiling were recruited from the

University of Guelph campus through online and poster advertisements. In each trial, PN combined with ultra-flash profiling (UFP) was conducted to collect attributes related to appearance, flavour and texture in 3 separate tests. Attributes within each of these sensory modalities play an important role in sensory appeal and would help in understanding the effect of hydrocolloids on attributes affecting consumer perception. Research ethics approval was obtained from the University of

Guelph Research Ethics Board (13JN001).

Before starting the test, judges were briefed about the concept and procedure of Napping® and the purpose of conducting this research. Each participant was provided with a 40 cm X 60 cm paper

(‘nappe’), pencil, post it notes and a paper with instructions. These instructions were also verbally explained before starting the evaluation. The paper version was given as a reference while doing the evaluation. In order to have a better understanding of this exercise, a small demo with six different cereals was given so that everyone was clear about the way samples were to be placed, emphasising the idea of using the whole sheet of paper for placing the samples rather than a small corner or just in a single line. Cereals were used as demo samples as they were totally different than the research samples of pureed carrots (Veinand, Godefroy, Adam, & Delarue, 2011). It was

68 explained that all of the nine samples had to be placed on the nappe in such a way that similarities and differences are explained by the distance between them – similar samples closer to each other and different samples farther away. All the samples were provided simultaneously and re-tasting was allowed during testing and placing of the samples. Post-it notes were provided to capture the descriptors coming to mind while tasting the samples. After all the samples had been placed (partial napping), the location of each was marked with an ‘X’. The code provided on the cup was written beside the ‘X’ and a few descriptors characterizing that sample were noted on the sheet (ultra-flash profiling). It was emphasised to participants that the descriptors should be specific to the sample and not in comparison to other samples such as ‘Sample A more red than Sample B’. It was explained that placement of samples on nappe was based on individual perception and there was no right or wrong answer in this decision. For each sensory modality, the instructions and methodology used were similar. In order to reduce the effect of fatigue, a gap of 10 minutes was provided after each modality. Fresh samples with different 3-digit codes were provided during testing of each modality to reduce bias effect and to maintain sample serving temperature (55°C).

Each judge was provided with compensation of $30.00 for this test.

4.2.2.2 Sensory Evaluation: Trained Panel

Based on the results of partial napping of texture, sensory evaluation with a trained panel was conducted to obtain quantitative results for comparison with instrumental results. Nine trained panelists from the University of Guelph were selected through e-mail correspondence, six of whom had already participated in trained panels for other food products. All of the texture descriptors from the napping study were classified into a few parameters and discussed with the trained panel.

A consensus was reached to finalise five attributes for evaluation considering the purpose of

69 research. Panelists were trained for 14 hours. Training included finalising the definition of texture terms, discussing the procedure of evaluating each term, determining the quantity of sample to be used during evaluation and the sequence to be followed while testing. Evaluation testing techniques were described in detail such as how to manipulate sample in the mouth and the number of chews before swallowing in order to come up with precise definitions of how to evaluate the sample. During the final stages of training attribute intensity for each sample was quantified on a

15 cm line scale in relation to the value assigned to reference / anchors selected for each term to be evaluated (Table 4.1). During this time, panel results were checked regularly to ensure reproducibility.

Following training, testing was carried out. Testing was conducted in sensory booths where data was entered into a computer with Compusense® Five (Compusense, Guelph, Ontario, Canada) software. Three replications of testing were completed. During each testing session, standard sensory testing protocols were followed with sample presentation randomized for each participant and all samples were labelled with three digit blinding codes. Panelists were compensated with

$15 for each session of training and testing. Evaluation of the sample attributes was completed using two teaspoonful of sample (Table 4.1). For all five attributes the intensity on the 15 cm line- scale ranged from low intensity (0) to high intensity (15) such as low smooth to high smooth

(smoothness), airy to dense (denseness), low adhesiveness to high adhesiveness, low cohesiveness to high cohesiveness and low oil mouth-coat to high oil mouth-coat as indicated in Table 4.1.

Table 4.1 – Attributes evaluated by trained panel with definition and references used along with their intensity values on a 15cm line scale.

Intensity Sampling value on a Attribute Definition Reference Used Technique 15 cm Scale Compactness of the Gay lea Real Whipped 1.5 sample, how much Cream air / solid mass like Betty Crocker Whipped Denseness 9.0 feeling it has when Cream Cheese Frosting pressed against the Philadelphia Whipped roof of the mouth. 12.5 Regular Cream Cheese (Airy----Dense) Cream of Wheat 2.5 Velvety feeling of First Creamy Brown Rice the sample in the spoonful Smoothness Organic Wholegrain 7.0 mouth Baby Cereal (Low Smooth---- Snack Pack Chocolate High Smooth) 14.0 pudding Stickiness of the Snack Pack Butterscotch 3.5 – 4.0 sample Pudding Adhesiveness (Low Adhesiveness-- Fluffernutter 7.5 – 8.0 --High Marshmallow Fluff Adhesiveness) Nutella 14.0 Degree to which the No name Tapioca 3.0 mass of food and Pudding saliva hold together Cohesiveness after mastication and while swallowing Betty Crocker Whipped 12.0 (Low Cohesiveness-- Cream Cheese Frosting --High Cohesiveness) Second No name Mashed 1.5 spoonful Potatoes with just water Intensity of oily No Name Mashed coating in the inner Potatoes with ½ and ½ surface of mouth 7.5 Oily Mouth cream and 1 Tbsp. after the sample has Coating margarine been swallowed No Name Mashed (Low Oil----High Potatoes with 35% Oil) 12.5 cream and 2 Tbsp. margarine

4.2.3 Data Analysis

4.2.3.1 Napping®

Data for each of the two trials was analyzed separately. For the analysis, data from each judge’s nappe was measured in the form of coordinates (X and Y) for each sample by measuring the sample location using the bottom left corner of the nappe as the origin and noting the descriptors associated with each sample. This was done for all judges and entered separately for attributes in the three sensory modalities. Data were analyzed by Multiple Factor Analysis (MFA) using

XLStat 2010 (Addinsoft, www.xlstat.com) (Louw et al., 2013). For this analysis, measured data were entered in an excel sheet with coordinates for each judge in columns and samples in rows, 9 rows (9 samples) and 22 columns (2 columns / person for X & Y coordinate data as in the case of first trial). An example spreadsheet is shown in Figure 4.1. These are the active variables which are used for construction of axes and to show representation of pureed samples (Perrin et al., 2008).

A large pool of descriptors was obtained in this test. This number was reduced by grouping recurrent terms as well as synonyms through discussion with a sensory research expert, to get a clear understanding of samples with their associated terms (Albert et al., 2011; Ko & Hong,

2014).The descriptors were then listed in columns as supplementary variables with a count of the number of times an attribute was mentioned by the judges. For instance, if the attribute was mentioned by three judges for a particular sample, then a value of ‘3’ was assigned for that attribute. A value of ‘0’ was recorded if the attribute was not mentioned for a sample. These descriptors will be used to characterize the pureed samples based on their correlation coefficient with the factors of MFA. They will not be used in the construction of axes for MFA (Pagès, 2005;

Perrin et al., 2008).

Judge1 Judge2 -- Judge 12 No. of times each attribute is used by all the judges Samples X1 Y1 X2 Y2 -- X12 Y12 Attribute1 Attribute Attribute Attribute ------1 2 19 20

------ThickenUp® Count2 Count Count Count

------MCS(i) Count Count Count Count

Unipure

Xanthan

Pectin

CMC

Gellan

Carrageenan Count Count Count Count

Commercial Count Count Count Count

Figure 4.1 – Structure of Data Table for Multiple Factor Analysis for Napping ®

1For appearance, the number of attributes was 44 in trial 1 (11 judges) and 62 attributes (13 judges) in trial 2. For flavour, the number of attributes was 35 in both trials (11 judges in trial 1 and 12 judges in trial 2). For texture, the number of attributes was 37 in both trials (11 judges in trial 1 and 13 judges in trial 2).

2Count denotes the number of times each attribute is assigned for a particular sample by all the judges. If a particular attribute is not used by any of the judges, it is assigned a value of ‘0’.

4.2.3.2 Trained Panel

Data from the trained panel was exported from the data collection software and analyzed using

Panelists were treated as random effects and samples and replicates were fixed effects. When significant differences among samples were observed, further analysis was conducted by a Least

Square Means procedure to identify specific differences within a particular attribute.

4.3 RESULTS AND DISCUSSION

4.3.1 Effect of hydrocolloids on Appearance, Flavour and Texture of pureed carrots: Napping® Results

Napping has been successfully used to obtain rapid results about consumer perception and sensory descriptors for product development (Albert et al., 2011). Analysis of the data from the current research using MFA gave a graphical representation of all samples on a two – axis Euclidean space. A factor is characterised by its eigenvalue which represents the variance of the dataset explained by the factor; the first factor explains the highest percent of variance and every other factor describes the variance not explained by the previous factor. Factors are calculated using the active variables (co-ordinates of each panelist). Supplementary variables (sensory descriptors) are projected on to these factors. The distance between samples on the graph represents their perceived similarities and differences; the closer the samples, the more similar they are. Although two partial napping trials were completed during this research, results for only the second trial of all three sensory modalities are discussed here as a larger number of judges were involved with the second

74 trial. A visual comparison of the results from the two trials revealed that they were similar. Partial napping has been found to give similar results across panels (Grygorczyk, Lesschaeve, Corredig,

& Duizer, 2013; Dehlholm, Brockhoff, Meinert, Aaslyng, & Bredie, 2012).

Results are discussed as per the order of sensory testing – Appearance, Flavour and Texture. The tables and figures are in the same sequence for each modality and are followed by a discussion of results.

4.3.1.1 Appearance

Table 4.2 indicates the eigenvalues and percent of variance for first four factors. These together explained 86% of cumulative variability. The importance of a sample in a particular factor / dimension is shown by its percentage contribution for that particular factor (Perrin et al., 2008).

The ‘factor score’ of each sample explains the co-ordinates / position of sample along the axis of a factor (Abdi, Williams, & Valentin, 2013). Factor score and percent contribution of all samples for the first four factors is shown the Appendix B. The graphical representation, also known as the product map, of all samples based on their factor scores is depicted in Figure 4.2. These two values, factor score and percent contribution, give an idea about the sample(s) which explain the most variability in a particular factor. This can then be correlated with attributes given in Table 4.3.

Attributes with a correlation ≥ 0.60 are considered important in explaining the sample and factor

(Grygorczyk, 2012).

Table 4.2 - Eigen values and percent of variance for major dimensions of partial napping (appearance) using multiple factor analysis.

Factor 1 Factor 2 Factor 3 Factor 4

Eigenvalue 8.82 4.39 1.96 1.72

Percent of Variance 44.89 22.37 9.97 8.75

Cumulative Percent of 44.89 67.25 77.22 85.97 Variance

Table 4.3 - Correlation of attributes / descriptors (supplementary variables) with first four dimensions of Multiple Factor Analysis for Partial Napping (Appearance). The usage frequency of each attribute is also included. Correlation ≥ 0.6 is highlighted in bold and correlations between 0.5800 – 0.6000 are highlighted in bold italics.

Correlation with Dimensions Usage Attribute Dim Dim Dim Dim Frequency (F1) (F2) (F3) (F4) Smooth 31 -0.874 -0.058 -0.125 0.006 Slightly smooth 4 0.012 0.726 0.484 -0.110 Very smooth 3 -0.600 -0.380 -0.023 0.326 Weak 2 0.614 -0.023 0.144 0.458 Shiny 9 -0.379 0.220 -0.732 0.218 Thin 3 -0.686 -0.362 -0.515 0.215 Grainy 5 0.634 -0.581 0.134 0.315 A little rough 3 -0.336 -0.020 -0.056 -0.589 Rough 7 0.700 -0.396 0.123 -0.262 Rough surface 4 0.868 0.331 0.008 0.202 Chunky 3 0.517 -0.052 -0.587 0.162 Shiny surface 3 -0.336 -0.020 -0.056 -0.589 Smooth surface 2 -0.656 -0.373 0.053 0.426 Low surface smoothness 4 0.868 0.331 0.008 0.202 Moderate surface smoothness 3 -0.336 -0.020 -0.056 -0.589 High surface smoothness 2 -0.656 -0.373 0.053 0.426 Clumpy 8 0.841 -0.027 -0.059 0.131 Dull 8 0.817 -0.341 -0.244 -0.135 Light orange 9 0.172 -0.296 -0.287 -0.586 Medium orange 9 -0.712 -0.047 0.112 -0.073 Bright orange 25 -0.920 0.133 -0.003 0.055 Dark orange 4 0.171 0.762 0.295 0.048 Light orange red 2 0.275 0.853 0.004 0.355 Red orange 4 -0.320 0.401 0.048 0.653 Yellow / Orange 4 0.133 -0.001 0.288 -0.717 Yellow 7 0.670 -0.606 -0.067 0.273 Bubbly 2 -0.161 -0.050 -0.843 -0.242

Appearance (axes F1 and F2: 67.25 %)

4 ThickenUp® Carrageenan

Pectin

0 MCS (i) Xanthan Gellan

F2 (22.37 %) (22.37 F2 CMC

-2 Unipure

Commercial -4 -4 -2 0 2 4 6 F1 (44.89 %)

Figure 4.2 - Product Map generated using Multiple Factor Analysis of Appearance data on Factor 1 and Factor 2.

The first dimension (F1) was described by a large number of highly correlated attributes (Table

4.4). Samples on both axes (F1 and F2) were characterized by appearance attributes of surface texture and colour. CMC and Unipure were characterised as smooth, thin, high surface smoothness, and bright orange colour. The commercial sample on the opposite end of F1 axis was characterised with low surface smoothness, rough surface, weak, yellow colour and a dull sheen.

ThickenUp® and carrageenan, being positive on dimension 2 and commercial being negative on this dimension, play a major role in construction of dimension 2. The descriptors for the

78 commercial sample in this dimension are similar to that in dimension 1 with grainy texture and yellow colour. ThickenUp® and carrageenan were described as slightly smooth with light orange red/dark orange colour.

Considering the fact that xanthan singly contributed 63% in the construction of dimension 3, it can be strongly associated with the attributes of bubbly and shiny. Dimension 4 had 39 % contribution from MCS (i) which is characterised as a little rough, shiny surface, moderate surface smoothness and yellow / orange/light orange colour. These are also shared by gellan to a lesser extent with has

19% contribution in this dimension. CMC is again attributed red orange colour in this dimension as described in dimension 1.

These results indicates that hydrocolloids affect the appearance of pureed carrots by way of differences in colour, surface texture and sheen of pureed carrots. Aside from the commercial sample which was described as a yellow colour, pureed carrot formulations with different hydrocolloids ranged from medium orange colour to bright / dark red orange colour. Others have also observed differences in colour due to hydrocolloid addition. Mashed potatoes with different hydrocolloids showed differences in greenness and yellowness, both instrumentally and by trained panel results (Fernández et al., 2008). Visible colour differences have been also observed by a trained panel evaluating ice cream with different hydrocolloids (Soukoulis et al., 2010). Vegetable purees with hydrocolloids added as cryoprotectants were not different in colour, however this may be due to lower concentrations of these hydrocolloids added to the vegetables in comparison to the concentrations used in the current research (Downey, 2002).

4.3.1.2 Flavour

Table 4.4 indicates the eigenvalue and percent of variance explained by first four axes of MFA which together explain about 77% of variability. The coordinates of each sample in the product map (Figure 4.3) are as shown in Appendix B which also gives the percent contribution of each sample on a particular factor or dimension. Correlations of flavour descriptors with each factor along with their frequency of usage are shown in Table 4.5.

Table 4.4 - Eigen values and percent of variance for major dimensions of partial napping (Flavour) using multiple factor analysis.

Factor 1 Factor 2 Factor 3 Factor 4

Eigenvalue 5.27 3.33 2.70 2.07

Percent of Variance 30.32 19.15 15.52 11.91

Cumulative Percent of 30.32 49.47 64.99 76.90 Variance

Table 4.5 - Correlation of attributes / descriptors (supplementary variables) with first four dimensions of Multiple Factor Analysis for Partial Napping (Flavour). The usage frequency of each attribute is also included. Correlation ≥ 0.6 is highlighted in bold and correlations between 0.5800 – 0.6000 are highlighted in bold italics. Usage Correlation with Dimensions Attribute Frequency Dimension (F1) Dimension (F2) Dimension (F3) Dimension (F4) Medium carrot flavour 8 0.440 -0.710 0.093 0.334 Very weak carrot flavour 4 -0.759 -0.179 0.114 -0.535 Strong carrot smell 3 0.363 0.636 -0.363 -0.139

Medium carrot smell 2 -0.068 -0.219 0.740 0.057 Not bitter 2 0.087 -0.151 0.541 0.594 Bitter 16 0.119 0.128 -0.193 0.739

Very bitter 5 0.395 0.240 -0.604 -0.283 Metal 2 -0.487 0.757 -0.001 -0.261 Citrus 2 0.285 0.859 0.131 -0.159

Mild sour 3 0.152 0.667 0.317 0.460 Sour 4 0.330 0.756 0.184 -0.072 Not sweet 3 -0.058 -0.100 0.720 0.285

Salty 7 -0.895 0.095 -0.159 -0.193

Smells like chicken 2 -0.929 0.143 -0.133 -0.186

Pea flavour 5 -0.929 0.143 -0.133 -0.186 Spicy 2 -0.929 0.143 -0.133 -0.186

Flavour (axes F1 and F2: 49.47 %)

Pectin

1 Commercial F2 (19.15 %) (19.15 F2 Xanthan ThickenUp® 0 Gellan

-1 MCS (i) CMC Carrageenan Unipure -2 -7 -6 -5 -4 -3 -2 -1 0 1 2 F1 (30.32 %)

Figure 4.3 - Product Map generated using Multiple Factor Analysis of Flavour data on Factor 1 and Factor 2.

The commercial sample and pectin are rated very differently in flavour compared to rest of the samples and are therefore quite far from the origin and from other samples as shown in Figure 4.3.

This is further exemplified by the number of descriptors associated with these two samples. The commercial sample has 5 descriptors on dimension 1with correlation values between 0.8 - 0.9 and pectin has 5 descriptors with correlation values between 0.6 - 0.9. Flavour attributes associated with the commercial sample include very weak carrot flavour, pea flavour, salty and a chemical

82 stimulus of spicy. It was also described as smells like chicken. These characteristics are present only in commercial sample, which makes it a stand-alone sample. Pectin also stands alone on dimension 2 because of its distinct chemical feeling of metal, sour taste and citrus flavour. It was also associated with a strong carrot smell. Carrageenan placed on the other side of dimension 2 has a medium carrot flavour. Data for dimension 3 show that ThickenUp® and MCS (i) are described as very bitter while xanthan and carrageenan as not sweet with medium carrot smell.

Dimension 4 has contributions from xanthan and MCS (i) and a correlation with bitter taste.

Hydrocolloids affect release of aroma compounds depending on their molecular weight, polarity and binding interactions with the ingredients in the food matrix (Gallardo-Escamilla et al., 2007;

Guichard, 2002). Aroma compound release is also dependent on viscosity of the final product

(Gallardo-Escamilla et al., 2007; Wendin, Solheim, Toomas, & Johanssona, 1997). With regard to specific hydrocolloids, xanthan addition has been shown to increase the sweetness of ice cream, decrease the sweetness of sour milk and found to enhance yogurt flavour in fermented whey

(Soukoulis et al., 2010; Gallardo-Escamilla et al., 2007; Wendin et al., 1997). Xanthan has also been found to reduce the sweetness of mashed potatoes (Fernández et al., 2008). In the current study, xanthan was not associated with sweetness, but with a bitter taste in the pureed carrot formulations. Starch and carrageenan addition reduces sweet taste in vanilla custard (de Wijk, van

Gemert, Terpstra, & Wilkinson, 2003). Similar results have been observed with carrageenan in the current study. While pectin is found to decrease sourness in sour milk and acid flavour in whey drinks and contributed no off-taste in mashed potatoes, in the current study pectin is rated high in citric and sour taste (Fernández et al., 2008; Gallardo-Escamilla et al., 2007; Wendin et al., 1997).

These results show that that flavour release is dependent on molecular structure and concentration

83 of hydrocolloids and the mechanism of interaction with aroma compounds in food matrix. Overall, due to the strong flavours/tastes associated with pectin and the commercial sample, all the other hydrocolloids were grouped almost together with very few descriptors with significantly high correlations.

4.3.1.3 Texture

With regard to texture, the first four axes explain 77% of sample variability (Table 4.6). Factor scores of each sample as graphically represented in the product map (Figure 4.4) and their contribution in the construction of axis for each dimension is shown in Appendix B. The list of descriptors, their usage frequency and correlation with first four axes is as shown in Table 4.7.

Table 4.6 - Eigen values and percent of variance for major dimensions of partial napping (Texture) using multiple factor analysis.

Factor 1 Factor 2 Factor 3 Factor 4

Eigenvalue 6.88 3.46 2.52 2.06

Percent of Variance 35.69 17.93 13.08 10.69

Cumulative Percent of 35.69 53.62 66.69 77.38 Variance

Table 4.7 - Correlation of attributes / descriptors (supplementary variables) with first four dimensions of Multiple Factor Analysis for Partial Napping (Texture). The usage frequency of each attribute is also included. Correlation ≥ 0.6 is highlighted in bold and correlations between 0.5800 – 0.6000 are highlighted in bold italics.

Usage Correlation with Dimensions Attribute Frequency Dimension (F1) Dimension (F2) Dimension (F3) Dimension (F4) Low smooth 2 -0.183 0.676 -0.262 -0.140

Smooth 36 0.621 0.244 0.617 0.250

Very smooth 6 0.617 -0.544 -0.422 -0.190

Slimy 10 0.639 -0.581 -0.043 -0.023

Viscous 4 0.165 -0.875 0.157 -0.088

Grainy 8 -0.759 -0.214 0.032 0.499

Pasty 4 -0.705 -0.436 0.423 -0.065

Very sticky 6 0.733 -0.478 -0.305 0.118

Thick mouth feel 3 0.016 0.146 -0.588 -0.541

Sticks when Swallowed 3 0.085 -0.866 -0.144 -0.015

Drying 4 -0.616 -0.265 0.315 0.324

Slightly wet 6 -0.430 -0.094 -0.645 -0.061

Thick 16 -0.731 0.015 -0.347 0.538

Thin 3 0.259 -0.148 0.167 -0.622

Texture (axes F1 and F2: 53.62 %)

3 ThickenUp®

2 Carrageenan MCS (i)

1 Pectin Gellan 0

CMC F2 (17.93 %) (17.93 F2 -1 Unipure

-2

-3 Commercial Xanthan

-4 -6 -5 -4 -3 -2 -1 0 1 2 3 4 F1 (35.69 %)

Figure 4.4 - Product Map generated using Multiple Factor Analysis of Texture data on Factor 1 and Factor 2.

The commercial and Unipure samples together contribute around 67% in the construction of dimension 1. The texture descriptors for the commercial sample indicate that the sample is grainy, pasty, drying and thick. Conversely, Unipure located on the opposite side of dimension 1 is described as smooth, slimy and very sticky. These attributes are shared with xanthan too, which is also strongly associated with dimension 2. Xanthan and the commercial sample are characterised as viscous and sticks when swallowed. ThickenUp® is described as low smooth. Carrageenan with

40% contribution in dimension 3 can be associated with slightly wet and thick mouth feel. CMC

86 being on the opposite side of this dimension was characterised as smooth. MCS (i) and pectin together account for > 70% contribution in dimension 4 and the texture for pectin can be described as thin. Further discussions about the Napping® results for texture will be discussed in section

4.4.3.

4.3.1.4 Summary of Napping Results

A summary of descriptors assigned to each thickener for the three tested sensory modalities is given in Table 4.8. The samples with most distinct attributes had more attributes associated with them. ThickenUp®, xanthan, carrageenan and commercial had descriptors for three tested sensory modalities while the rest had none associated with them either for one or two modalities. According to Perrin et al., (2008), Napping with UFP reveals the criteria which are important for discrimination and not the subtle differences.

For appearance, the samples were grouped in pairs; MCS (i) – gellan, carrageenan - ThickenUp®,

Unipure – CMC; except for pectin, xanthan and commercial. Commercial had the least smoothness and yellow colour while Unipure – CMC were the most smooth and bright orange colour. Rest of the hydrocolloids lied in-between. Commercial had a dull sheen while MCS (i), gellan and xanthan were described as shiny. Xanthan had a discriminating attribute of bubbly.

For flavour, commercial and pectin were most distinct and probably skewed the number of descriptors associated with other hydrocolloids. Commercial was described as having a pea flavour, spicy, salty and a chicken smell. Pectin had a citrus, sour flavour with strong carrot smell.

Pureed carrot formulations with ThickenUp®, MCS (i) and xanthan had a bitter flavour.

For texture, xanthan had more similarities with Unipure and a few with commercial. CMC,

Unipure and xanthan had a smooth texture while ThickenUp® was described as low smooth and commercial with grainy texture. Carrageenan had distinct attributes as having a thick mouthfeel and pectin was described as thin.

Table 4.8 - Summary of attributes obtained for three tested sensory modalities of pureed carrots formulations with different hydrocolloids using partial napping.

Hydrocolloid Appearance Flavour Texture Slightly Smooth, Light Orange Very Bitter Low Smooth ThickenUp® Red / Dark Orange Colour

A Little Rough, Shiny Surface, Very Bitter MCS (i) Moderate Surface Smoothness and Yellow / Orange (light orange) Smooth, Thin, High Surface Smooth, Very Smoothness, Bright Orange Unipure Sticky, Slimy Colour

Smooth, Very Not Sweet, Sticky, Slimy, Xanthan Bubbly, Shiny Medium Carrot Viscous, Sticks Smell, Bitter When Swallowed Metal, Citrus, Sour, Strong Thin Pectin Carrot Smell

Smooth, Thin, High Surface CMC Smoothness, Bright Orange / Red Smooth Orange Colour

A Little Rough, Shiny Surface, Gellan Moderate Surface Smoothness and Yellow / Orange (light orange)

Medium Carrot Slightly Smooth, Light Orange Flavour, Not Slightly Wet, Carrageenan Red / Dark Orange Colour Sweet, Medium Thick Mouthfeel Carrot Smell

Very Weak Carrot Low surface smoothness, Rough Grainy, Thick, Flavour, Pea surface, Grainy, Weak, Yellow Pasty, Drying, Commercial Flavour, Salty , colour, Dull Viscous, Sticks Spicy, Smells Like When Swallowed Chicken

4.3.2 Effect of hydrocolloids on texture of pureed carrots: Results of Trained Panel Evaluation

Using the texture attributes collected during partial napping of texture as a guide, a trained panel evaluated the pureed carrot formulations with different hydrocolloids for five texture attributes.

ANOVA results (Appendix C) indicate significant differences among the samples for all attributes.

Mean scores for the attributes for each sample are shown in Table 4.9.

Carrageenan was perceived to be the densest sample, least smooth, with lower values for adhesiveness and oily mouthcoating and higher value for cohesiveness. Unipure, xanthan and

CMC were similar in all five attributes. These three were perceived to have a high oily mouthcoating compared to the other hydrocolloids. ThickenUp® and pectin had similar rankings for the five attributes and were characterised as very smooth. Gellan was rated highest for cohesiveness and low for denseness, smoothness and oily mouth-coating. Sensory textural attributes were mostly similar for the two modified corn starches except denseness.

The commercial sample showed similarities in texture with different hydrocolloids for different attributes such as with MCS (i) and gellan for denseness, carrageenan for smoothness and carrageenan, gellan, pectin, ThickenUp® and MCS (i) for the sensory perception of oily mouth coating.

Table 4.9 – Mean scores and standard deviations from trained panel for pureed carrot formulations with different hydrocolloids. Means with the same letters within a column are not significantly different for each attribute (p < 0.05).

Attributes

Samples Denseness Smoothness Adhesiveness Cohesiveness Oily Mouth Coating

Mean±SD Mean±SD Mean±SD Mean±SD Mean±SD

ThickenUp® 6.4±2.1c 11.5±2.2ab 6.9±2.2ab 7.0±2.4b 6.5±1.7b

MCS (i) 8.6±2.3b 10.6±2.2b 7.4±2.2ab 8.1±2.5abc 6.6±1.9b

Unipure 5.0±2.7cd 12.6±1.5a 7.3±3.4ab 6.8±2.3c 9.8±1.7a

Xanthan 4.7±1.7d 12±2.2ab 8.0±2.8a 6.7±2.3c 10.2±2.4a

Pectin 6.2±1.6cd 11.0±1.8b 8.0±1.8a 7.1±2.3abc 6.7±1.9b

CMC 5.4±2.3cd 11.7±2.0ab 8.1±2.4a 7.2±1.9abc 9.3±1.8a

Gellan 9.5±2.4b 7.5±1.9c 7.1±2.3ab 8.9±2.3a 7.0±2.2b

Carrageenan 12.2±2.2a 4.5±2.3d 5.7±2.4b 8.8±2.7ab 6.1±2.1b

Commercial 9.3±2.6b 4.8±1.4d 7.3±2.5ab 7.1±3.0abc 5.5±3.4b

Difficulty in swallowing is a function of textural attributes perceived during initial stages of oral processing (Hayakawa et al., 2014). This varies with the type and concentration of thickeners.

Hydrocolloids affect texture of food giving differences in sensory perception, as observed in the current research. Previous research has shown that modified corn starch provided a firm texture and high slipperiness to pureed carrot formulations compared to un-thickened carrots as well as other thickeners such as rice cereal and skim milk powder (Ilhamto, 2012). Xanthan has been associated with providing significant creaminess, lubricating and coating properties in mashed potatoes similar to being perceived high in oily mouthcoating in current pureed carrots formulations (Fernández et al., 2009; Alvarez, Canet, & Fernández, 2008). Also xanthan was found to reduce granularity in mashed potatoes and also in our pureed carrots formulations, it is ranked high for to smoothness (Alvarez et al., 2008). Carrageenan was regarded to impart lesser homogeneity in mashed potatoes, an attributed related to degree to which the sample is free of particles or irregularities (Fernández et al., 2009). Carrageenan was rated low for smoothness for pureed carrot formulations. This shows that texture of pureed products perceived during oral processing varies with hydrocolloid type, concentration and food matrix.

It was interesting to know that the trained panel had decided to include oily mouthcoating as an attribute for evaluating the samples. It was included by group consensus after few tasting sessions.

The pureed carrot formulations had no component of fat and / or oil but the afterfeel sensation was so strong in some that oily mouthcoating had to be included for sensory evaluation. Mouthcoating is an important attribute for product liking, especially in case of diets for older adults, which has received very little attention in the past (Withers, Gosney, & Methven, 2013). It is observed from

92 the results of trained panel that the samples are quite clearly demarcated with respect to the attribute of oily mouthcoating.

Good sensory appeal combined with nutrition in pureed foods can increase daily intake, allowing individuals to maintain regular weight and health (Hall & Wendin, 2008; Rothenberg et al., 2007).

Nutrient dense pureed foods contribute to an increase in body weight and micronutrient level

(Adolphe et al., 2009; Germain et al., 2006). Sensory evaluation helps to understand the texture of food as perceived during the mastication process. Detailed sensory profiling will help in designing pureed foods which are safe, in addition to having appropriate flavours and appearance.

4.3.3 Comparison of trained panel and Napping® (texture) results

Because Napping® uses consumers, results will not be entirely similar to those from the trained panel which had experts evaluating the samples. These panelists had undergone training and decided on intensity values through group consensus. Studies have shown similar product configuration between Napping® and DA (Louw et al., 2013; Albert et al., 2011) although the output from DA is typically more robust and contains detailed information about the products.

Since Napping® allows free choice of words; sometimes it becomes arbitrary and difficult to understand the exact meaning of the descriptor such as difference between weak and thin in case of appearance, slightly wet used in texture. Napping discriminates products with distinct differences but where differences are not very prominent, not much information can be gained such as in case of gellan for partial napping of texture. Also quantitative data needed for understanding relations, significant differences and comparisons can be obtained using trained panel evaluations.

In general, Unipure, xanthan and CMC were rated similarly for all attributes by the trained panel.

Somewhat similar results were observed from the consumer Napping® panel (Fig 4.4). Unipure and xanthan had higher values for adhesiveness and described as very sticky and slimy in

Napping®. Unipure and CMC perceived to be high on smoothness by the trained panel which was similar to the terms of smooth in Napping®. The commercial product was perceived as least smooth by the trained panel and described as grainy, coarse and very low smooth by consumers. Pectin described as thin in Napping® was assigned a score of 6.2 on 15cm line scale of denseness going from low denseness (0) to high denseness (15). One sample with a discrepancy between the trained panel and consumers was ThickenUp® which was rated to be very smooth by the trained panel and described as low smooth in Napping®. Carrageenan was characterised with thick mouthfeel which was not consistent with trained panel ‘after-feel’ data. This may be due to the fact that trained panelists were specifically capturing ‘oily mouthcoating’ which is a different attribute than thick mouthfeel. It may be possible that the thick mouthfeel was related to denseness in trained panel testing which then proves it to be correct as carrageenan was ranked as the densest sample.

4.4 CORRELATIONS OF INSTRUMENTAL AND SENSORY MEASUREMENTS

It is not possible to understand complex sensory perceptions with a single instrumental test but inter-relationships between important sensory textural attributes and mechanical parameters will help in the formulation of right texture foods (van Vliet, 2002). Statistically significant correlations were obtained between two instrumental measurements and sensory which helps in better understanding the behaviour of hydrocolloids in pureed carrots (Table 4.10).

Positive correlations were obtained between sensory denseness and complex modulus, complex viscosity, yield point, viscosity at 10 s-1 and gumminess. Research in the past have found strong

94 correlation between these instrumental measures and oral thickness. Oral thickness has been positively related to yield stress of whey protein based fat free dairy desserts (Vidigal et al., 2012).

Sensory perception of thickness has also been correlated with yield stress, complex viscosity and apparent viscosity at 10 s-1 of commercial dairy desserts (Tárrega & Costell, 2007). Oral perception of thickness has been correlated to viscosity at 10 s-1 in many other studies as found in the current study (Cutler, Morris, & Taylor, 1983; Shama & Sherman, 1973). Higher complex viscosity results in higher levels of perceived thickness (Haghighi et al., 2011). Thickness was not included as a sensory attribute in trained panel testing as the samples were matched for viscosity at a shear rate considered to be operating during oral processing, 41–50 s-1. Similarities between correlations of thickness from earlier studies and denseness of current study indicate that may be this led to the dumping effect, owing to limiting the range of sensory attributes (Lawless & Heymann, 1998).

However this seems unlikely considering the references used for training the attribute of denseness, ranging from airy to dense, overlapping of denseness and thickness attribute cannot be completely ruled out. This may indicate that products matched for viscosity at a reference shear rate may not be perceived similar in thickness during oral manipulation. This needs to be further explored in future sensory studies especially in diets for people with swallowing disorders.

Complex modulus is a measure of strength / overall resistance of gels against deformation of a sample and gumminess is a measure of energy needed to make a swallow-able bolus and positive correlation of these parameters with denseness indicates that a firm sample will need more energy to deform.

Table 4.10 - Correlation of instrumental measures with sensory attributes. Significant correlations with p ≥ 0.05 are bolded.

Sensory Measurements Instrumental Oily Mouth Measurements Denseness Smoothness Adhesiveness - coating

Phase angle - 1 r value -0.63 0.68 0.45 0.77 Hz p value 0.07 0.04 0.23 0.02

Complex r value 0.69 -0.56 -0.60 -0.58 modulus - 1 Hz p value 0.04 0.12 0.09 0.10

Complex r value 0.69 -0.56 -0.60 -0.58 Viscosity - 1 Hz p value 0.04 0.11 0.09 0.10

r value 0.67 -0.58 -0.95 -0.38 Yield Point p value 0.05 0.10 <0.0001 0.31

Viscosity r value 0.82 -0.90 -0.51 -0.78 at 10 s-1 p value 0.007 0.0008 0.16 0.01

r value 0.54 -0.80 -0.24 -0.62 Hardness p value 0.14 0.02 0.53 0.07

Gumminess r value 0.67 -0.81 -0.39 -0.73 p value 0.05 0.009 0.30 0.02

Sensory smoothness was positively related to phase angle and negatively correlated with hardness, gumminess and apparent viscosity at 10 s-1. A sample with a higher viscous component has a higher phase angle. Higher viscous component is associated with a smoother oral perception

(Tobin, 2014). Less effort needed to compress and make a ready to swallow bolus indicates easy mixing with saliva and so may give the perception of sample smoothness.

Sensory adhesiveness had a high negative correlation to yield point. It has been positively related to yield stress in case of cream cheese which is a different product than pureed carrots (Kealy,

2006). Current study indicates that hydrocolloids which imparted a strong structure were perceived as less adhesive. Adhesiveness is related to spread ability and yield stress is related to ease of swallow and resistance to compression, so it is important to use the correlation of these two parameters for developing diets for people with swallowing difficulties (Tobin, 2014; Foegeding et al., 2011). The sensory attribute of cohesiveness did not correlate with any instrumental measures but correlated with other sensory attributes.

The sensory attribute of oily mouth-coating was positively correlated with phase angle and negative correlations with apparent viscosity at 10 s-1 and gumminess. This indicates that a firm sample with more solid-like characteristic will have less oily mouth-coating while a more viscous- oriented sample with less solid behaviour, resulting in higher phase angle will have more perceived oily mouth coating. Also a sample which requires less energy to make a swallow-able bolus will have a higher oily mouth-coating after swallowing.

The five important sensory attributes finalised for textural characterisation of pureed foods, after consumer sensory testing (partial napping of texture) included denseness, smoothness,

97 adhesiveness, cohesiveness and oily mouth-coating. The oscillatory test parameters of phase angle, complex modulus, complex viscosity and yield point correlated with four of sensory attributes except cohesiveness. Apparent viscosity at 10 s-1 and the TPA parameters of hardness and gumminess correlated with three sensory attributes. So, it is important to take all these parameters for designing safe-swallow foods. This reiterates the point that both rheological testing (SAOS and

LAOS) and texture profile analysis has to be done for understanding sensory perception and developing standards of pureed foods.

4.5 CONCLUSION

The objective of this research was to look at the effect of hydrocolloids on sensory properties of pureed carrots. Napping and trained panel results showed that hydrocolloid type has an effect on many sensory properties even though the samples were matched for apparent viscosity at a shear rate of 50 s-1.

Hydrocolloids changed the colour, surface texture and sheen of pureed carrots. They imparted varying flavours ranging from bland, sweet, sour, and citric to bitter. The texture of pureed carrot formulations varied with hydrocolloids with some representing high smoothness, low denseness and low cohesiveness while some had a low smoothness, high denseness and high cohesiveness.

While sensory perception of textural attributes differed among hydrocolloids, it gave strong correlation with instrumental parameters which help in understanding oral processing and can be further used for developing diets for people with swallowing disorders, using different hydrocolloids. The results indicate that both viscous and elastic components contribute equally for safe-swallow food. Apparent viscosity at 10 s-1 had correlations with instrumental and sensory parameters while no correlations were found with viscosity at 50 s-1.

Chapter 5

5. OVERALL CONCLUSIONS AND RECOMMENDATIONS

The current research was undertaken with the objective of understanding the effect of hydrocolloid addition on texture of pureed foods meant for people with swallowing disorder / dysphagia.

Hydrocolloids used either in commercial pureed foods or currently being studied in thickened beverages were selected to understand their effect on texture and other sensory modalities in pureed carrots. Some of the hydrocolloids tested such as Unipure, xanthan and MCS (i) are manufactured specifically for use in dysphagia diets. ThickenUp® is the most common thickener used in Long Term Care Centres in making pureed foods therefore it was used as a reference sample for viscosity measurements. Although there is speculation regarding the oral shear rate operating during the mastication process, 50 s-1 is the most commonly used reference in literature and has also been adopted by National Dysphagia Diet (America) for guiding classification of dysphagia diets. As such the first step of this study was to determine the concentration of each selected hydrocolloid such that the apparent viscosity of all pureed carrot formulations was similar to the ThickenUp® (reference) at 50 s-1. It was hypothesized that hydrocolloids have no effect on texture and sensory properties of pureed carrots once the viscosity is matched at a shear rate of 50 s-1. One commercial carrot puree sample was also included for comparison.

It is important to know how the hydrocolloids affect the overall product acceptability and safety of consuming pureed foods starting from the initial stages of appearance, flavour, and texture for understanding the in-mouth perception. In the absence of any existing quantitative guidelines, this becomes more vital considering the fact that pureed foods available in the market are manufactured using one or more hydrocolloids without knowing the behaviour of these additions.

In this research, textural characterisation was done using instrumental measurements and sensory evaluation. This can be used to know how a pureed carrot sample is perceived with certain instrumental parameters. Instrumental measurements were made using both small and large deformation testing. Small deformation will show product characteristics at the molecular-level which can be associated with appearance of food served in a plate and initial perception of food when placed in food. Behaviour under large deformation testing will give an insight about texture when subject to mastication and other swallowing processes.

Modification of texture by hydrocolloids is accompanied by changes in appearance and flavour which affect the overall liking of foods. Human perception of pureed carrot samples was evaluated for both understanding intuitive perception and trained panel testing for textural attributes for comparing with instrumental measurements.

Instrumental characterisation of pureed carrot samples matched for viscosity showed that some textural properties were not different amongst hydrocolloids, while others were. Differences in sensory perceptions amongst hydrocolloids also existed. All hydrocolloids and the commercial sample behaved similarly in terms of extensibility of bonds (length of LVR – strain sweep), elastic behaviour (G´ - frequency sweep), and slope of complex viscosity (frequency sweep) during small deformation. Additionally, similarities were observed in the elasticity, or the extent to which the sample returned to its original size after first compression (springiness) as measured by large deformation. This reflects that the hydrocolloids had no differences on the elastic component or deformation energy stored in the sample either during small or large deformation tests. The differences across other instrumental measures, were subtle, but highlighted some important characteristics.

100

Carrageenan and pectin showed a strong while Unipure and CMC showed a weak structure strength under small deformation conditions. This is evident from the high values for G´LVR and G*. These two pairs showed similarities in their behaviour when G´ and G´´ were plotted across strain sweep and frequency sweep. The weak structure of CMC was substantiated with its higher slope value of G´ and G* and phase angle. When subjected to large deformation, pectin displayed a structure which was easy to deform, similar to CMC and different than carrageenan. It had a low yield point, low flow point and low values for hardness, gumminess and higher value for cohesiveness. Unipure shared some similarities with CMC under large deformation conditions but also had some similarities with carrageenan such as yield and flow point (rheology) and adhesiveness and cohesiveness (TPA). Other hydrocolloids displayed characteristics between these four discussed hydrocolloids. Exceptions to this included very high adhesiveness values for the two starches tested (MCS (i) and ThickenUp®), low adhesiveness for gellan and a high flow point for MCS (i). The reference sample and commercial sample behaved similarly for rheological tests (except for phase angle) but very different for TPA.

Sensory analysis of textural properties using trained panel showed that the hydrocolloids CMC,

Unipure and xanthan were similar from a texture perspective. Similarities also existed between

CMC and pectin except for the oily mouth-coating. It was interesting to observe that a closer look of instrumental results indicated xanthan behaving more closely to Unipure and CMC than rest of the hydrocolloids. The commercial sample shared similarities with the reference sample in three out of the five tested sensory attributes. Partial napping results for texture indicated some similarities with trained panel and instrumental results where CMC and

101

Unipure were placed close to each other in the product space with xanthan being not far off from these two. Pectin, gellan and carrageenan were in close proximity while the commercial sample was quite different.

The texture results indicated that hydrocolloids have some distinct differences but also some overlapping behaviour. This has to be further analysed considering other important drivers of sensory liking such as appearance and flavour. Appearance affects the initial intake of pureed foods where people with swallowing disorders might fear to eat when it is either too grainy or too smooth for fear of choking. Hydrocolloids affect the colour of final product and it is better to choose the ones which maintain original colour of the product. For instance a carrot puree should be orange in colour rather than yellow, as in the case of commercial sample. Flavour is also an important sensory modality which affects the liking and intake of foods. For instance, in this study although pectin shared similarities with CMC under large deformation and trained panel results, its distinct citrus and sour flavour might make it unacceptable. Similarly xanthan,

ThickenUp® and MCS (i) were attributed with bitter flavour. The commercial carrot puree had a combination of many hydrocolloids and was described as having a pea and chicken flavour, attributes not often expected in pureed carrots.

Although the differences in instrumental measures were subtle, they mean a big difference when seen from a prospective of someone who has swallowing difficulty. This research indicated that sensory perception of texture for pureed foods could be understood using a combination of small and large deformation instrumental techniques. Complete consumer evaluations, including liking of appearance and flavour have to be completed to understand the acceptability of the product. These hydrocolloids should also be tested in swallowing studies

102 to see how the pureed carrot sample behaves during bolus formation and swallowing.

Instrumental results gave values for structure strength, yield point, flow point, hardness, adhesiveness and gumminess ranging from carrageenan on one end to CMC on the other. How these behave in mouth now needs to be investigated. For instance, if two hydrocolloids give similar results in texture (sensory and instrumental), such as CMC and Unipure, then their in- mouth behaviour needs to be examined. During sensory panels consumers had described

Unipure as `sticks when swallowed`, which needs to be verified with experts in this area such as involving Speech Language Pathologist to ensure if it is safe to be used in dysphagia pureed- diets. Another important highlight of the study is the large differences in concentrations used for each hydrocolloid. For instance, Unipure was added at 5% but only 0.5% of CMC was required to provide similar viscosities. The effect of such large concentrations of hydrocolloid on product nutrition is not known and should be investigated.

Knowledge about the appropriate instrumental measures and quantitative guidelines for right- textured pureed foods is still at infancy. In this study, both gumminess (TPA) and viscosity at

10 s-1 had correlations with three sensory attributes among the five tested by trained panel.

Gumminess, an indicator of amount of energy needed to make a semi-solid food into a swallow-able bolus, is the product of hardness and cohesiveness from TPA (mimics human mastication) and hence can be considered a good measure for guiding pureed food preparation.

Also viscosity at 10 s-1 is a better measure of in-mouth perception compared to viscosity at 50 s-1. The findings of this research and finding solutions to some issues raised here with the help of swallowing studies and involving Speech Language Pathologist can help in setting appropriate instrumental range values for pureed foods.

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