Grain & Oil Science and Technology 2018, 1(2): 85-90 DOI: 10.3724/SP.J.1447.GOST.2018.18019

Effects of Addition on the Quality and Shelf Life of Chinese Steamed CHEN Di, WANG Jinshui*, JIA Feng, ZHANG Changfu

College of Biological Engineering, Henan University of Technology, Zhengzhou 450001, China

Abstract: The effect of adding sourdough with lactic acid bacteria (Lactobacillus plantarum M616) on quality and the sensory scores, specific volume, crumb firmness, and spread ratio of resultant Chinese steamed bread were studied. The moisture content of crumb and texture characteristics of the Chinese steamed bread with sourdough during storage were analyzed. In this study, 10%, 20%, 30%, and 40% of sourdough addition was investigated. The sourdough starter resulted in significant decrease in the water absorption, development time, stability, and farinograph quality number of the dough. The addition of sourdough improved the quality of Chinese steamed bread such as improving the sensory scores and specific volume, decreasing the crumb firmness, and a lower spread ratio was observed with an increase in the sourdough concentration up to 30%. Sourdough addition delayed a fast decrease in the moisture content of the Chinese steamed bread crumb during storage. The texture profile analysis of the bread crumb indicated that the addition of sourdough improved the quality and delayed the staling speed of Chinese steamed bread during storage. Moreover, inclusion of 30% sourdough produced the best protective effect on product staling. Keywords: Sourdough; Chinese steamed bread; Dough quality; Shelf life; Texture profile analysis

1 Introduction of crumb structure and unique CSB flavor. There is growing In China, Chinese steamed bread (CSB) is a kind of interest in CSB production using sourdough for fermentation. traditional wheat fermented food and is formulated with wheat Upon using sourdough, lactic acid bacteria (LAB) provide flour, water, and and processed by steam cooking[1]. CSB sour flavor while provide carbon dioxide during dough has been considered as a staple food and is widely consumed in fermentation. The use of sourdough is a long-known tradition North China and it accounts for 40% of the wheat consumption and still plays an important role in wheat-fermented food in China[2]. CSB is considered as a healthy food because production. Sourdough can be generally prepared by spontaneous of the absence of toxic products such as fermentation of a mixture of flour, water, and salt; in recent acrylamide and furan[3], and also possible low oil and sodium years,literatures have focused on the use of specific cultures [6] contents. The relatively low steaming temperature (100 ˝C) and control fermentation process . The quality of wheat food during their production might lead to better retention of diverse has been improved and the shelf life of wheat food has been [7-10] endogenous and added nutrients comparing to baked bread[4]. extended in this way . The use of sourdough in bread-making In general, CSB is freshly prepared at the point of sale via influences all aspects of bread quality. Technological effects of small in-house scale production, and therefore, the quality and the sourdough on flavor, texture, shelf life, and nutritional quality composition of the bread also depend on manual labor and of CSB depends on the bioconversion of flour components at [11] workers’ skills. Presently, owing to rapid urbanization in China dough stage . Apart from generating a unique flavor, the resulting in an increasing demand for CSB, there is a move by products of sourdough fermentation have been linked to various [12] large-scale manufacturers to use machinery to produce CSB with health benefits . However, CSB poses some challenges such a consistent quality and distribute them in the form of frozen as rapid staling onset and short shelf life. These factors have products to supermarkets[5]. restricted further development of their large-scale production Sourdough and yeast starter are both used for fermentation and are serious challenges to the CSB industry. of the CSB dough. During fermentation, carbon dioxide and Texture and appearance are two major sensory characteristics flavor components are produced, contributing to the development of cereal products. Therefore, the aim of this study is to analyze the influence of using different concentrations of sourdough in dough fermentation process on the texture and crumb grain Received: 7 November 2017 /Accepted: 23 March 2018. Supported by National Natural Science Foundation of China (31571780), Key characteristics of CSB and the effect of storage on these Research Project in Higher Education of Henan (18A550002), Zhengzhou characteristics, and to investigate possible relationships between Science and Technology Innovation Team Program (121PCXTD518), School texture and structural characteristics. Funds of Henan University of Technology (2017QNJH11), and High-level Talent Foundation of Henan University of Technology (2017BS005). 2 Materials and Methods *Corresponding author. E-mail: [email protected] 2.1 Materials ©Henan University of Technology 2018 CHEN D, WANG J S, JIA F, et al. Effects of Sourdough Addition on the Commercial white wheat is purchased from local market, Quality and Shelf Life of Chinese Steamed Bread[J]. Grain & Oil Science and which contains 12.7% protein, 0.43% ash, and 10.4% moisture Technology, 2018, 1(2): 85-90. content. Angel active dry yeast was provided by ANGEL YEAST 86 Grain & Oil Science and Technology 2018, 1(2): 85-90

Co., Ltd. (Yichang, China). Lactobacillus plantarum M616 was CSB was cooled for 15 min and the volume (seed displacement), isolated and stored in our laboratory. Farinograph water absorption, weight, diameter, and height were recorded. The CSB quality and the development and stability of the dough were determined was evaluated according to Chen et al.[13] The CSB quality by a farinograph equipped with a 50 g stainless bowl (Brabender score included the specific volume (weighting, 20), spread ratio Farinograph), according to the approved method, 54-21 of AACC. (10), skin (5), crumb color (5), shininess (5), smoothness (10), 2.2 Preparation of Sourdough Starter structure (10), and stress relaxation (35). Stress relaxation (SR) was assessed by Texture Analyzer TA-XT2i (Stable Micro L. plantarum M616 was grown in MRS broth at 35 ˝C for Systems, Ltd., Surrey, England). 16 h, and then transferred to 75 mL MRS broth (inoculation amount, 2%) at 35 ˝C for 8 h (cell counts, 109 cfu/mL). The cells 2.7 Moisture Content Analysis were obtained by centrifugation at 3000ˆg for 10 min, washed The moisture content of the samples was determined by twice with sterile water, and re-suspended in 10 mL of sterile gravimetric method. CSB samples were -dried at 100 ˝C water. Lactic acid bacteria fermentation starters were prepared and their weights were accurately recorded at regular intervals by mixing wheat flour and water (at a ratio of 1:1 W:W) and until a constant weight was reached. Three measurements were inoculated with 0.25 g of M616 strain pellet in 100 g flour. The performed for each sample. The moisture content is expressed starters were mixed and stored in sealed containers and fermented as grams of water over 100 g of the total weight (g/100 g). at 30 ˝C and 85% relative humidity (RH) until their pH reached 4. 2.8 Texture Analysis 2.3 Preparation of and Chinese Steamed Bread CSB was sliced transversely using a slice regulator The doughs were processed with wheat flour, active dry and knife to obtain uniform slices with 25 mm thickness. yeast (0.8%), water (the addition of water was determined Instrumental textural evaluation of the crumb was carried out according to water absorption in farinogram), and the sourdough using a universal testing machine (TA-XT2i Texture Analyzer, starter (10%, 20%, 30%, and 40%, referred to as SCM-1, Stable Micro Systems, UK) equipped with a 25 kg load. A speed SCM-2, SCM-3, and SCM-4, respectively). After mixing, the of 5.0 mm/s with a trigger force of 20 g was used to compress dough was divided (75 g/piece), rounded, molded manually, and the central area of the sample slice to 40% of its original height. proofed for 30 min at 33 ˝C and 75% RH. The proofed dough Each sample was compressed twice with a reciprocating motion was steamed for 15 min using a bamboo steamer and boiling to yield a two-bite texture profile curve. A range of texture water. Control CSB (CK) was fermented with active dry yeast, profile analysis (TPA) values were extracted from the resulting without sourdough starter. After cooling, the CSB samples were curve, including hardness, springiness, cohesiveness, chewiness, characterized, and then packed in polymeric bags and stored at 4 ˝C and resilience. The measurements were carried out on two slices for 3 days. Each dough treatment was processed in duplicate. taken from the center of the loaf. A crust penetration test was 2.4 Microbial Counts carried out on 10-mm-deep and 25-mm-wide crust pieces from 1 g of each dough sample was suspended in 10 mL of sterile the top of the loaf using a Stable Micro Systems blade set (Stable physiological saline and homogenized in a vortexer. To count Micro Systems, Godalming, UK). the number of L. plantarum M616 cells, each homogenate was 2.9 Statistical Analyses serially diluted ten-fold and spread on MRS agar containing 0.01 g/L cycloheximide as yeast inhibitor (GUL H 2005 and REHMAN TTA, pH, specific volume, form ratio, moisture content, S-U 2006). Culture dishes were incubated at 35 ˝C for 48 h. In and rheological parameters were determined four times each. order to count the yeast cells, each homogenate was spread on the Consequently, a variance analysis (ANOVA) was performed YPD medium without the inhibitor and incubated at 28 ˝C for 36 h. on each set of experimental values to determine the effect of fermentation at 95% or 99% level. 2.5 Deterination of pH and Total Titratable Acidity (TTA) The pH was determined according to the methods of AACC 3 Results and Discussion 02-52.01. 10 g dough was placed in a beaker containing 90 mL 3.1 Cell Counts of Doughs distilled water, mixed homogeneously, and then left for 30 min at As presented in Fig. 1 and Fig. 2, different microbial room temperature. The resultant supernatant was measured with a growth curves are obtained for dough samples with 10%, 20%, pH meter. For determining the total titratable acidity, 10 g wheat 30%, and 40% of sourdough and CK. Obviously, a trace amount sourdough was placed in a beaker containing 90 mL distilled water of LAB was found in the CK sample (Fig. 1). There were and vigorously stirred for 30 min. After that, 0.5 mL of a 1.0% no obvious change in cell counts during fermentation. The phenolphthalein indicator reagent was added, followed by titration cell counts in doughs increased with fermentation time and with 0.1 mol/L NaOH. The acidity was determined according to sourdough concentration. Moreover, the highest contents of the point at which a pink color was maintained for 30 s. LAB were found at 12 h of fermentation in all doughs, which 2.6 Evaluation of Chinese Steamed Bread Quality were prepared with different concentrations of sourdough. In Specific volume and form ratio of CSB were determined by particular, the LAB content of dough with 40% sourdough reach 9 methods described by Wu et al.[1] After the steaming process, the highest value at 12 h of fermentation (1.5 ˆ 10 CFU/g). CHEN D, et al. Effects of Sourdough Addition on the Quality and Shelf Life of Chinese Steamed Bread 87

12 9.5 CK CK SCM-1 9.0 SCM-1 10 SCM-2 SCM-2 SCM-3 8.5 SCM-3 ) SCM-4 SCM-4 8 )

(CFU/g) 8.0 10 (CFU/g) 10 6 7.5

7.0 4 Cell counts (log

Cell counts (log 6.5 2 6.0

5.5 0 4 8 12 16 20 0 4 8 12 16 20 Fermentation time (h) Fermentation time (h) Fig. 1 Growth curve of lactic acid bacteria during the Fig. 2 Growth curve of yeast during the dough fermentation CK, control dough; SCM-1, SCM-2, SCM-3, and SCM-4, doughs with dough fermentation 10%, 20%, 30%, and 40% of sourdough, respectively. CK, control dough; SCM-1, SCM-2, SCM-3, and SCM-4 are doughs with 10%, 20%, 30%, and 40% of sourdough, respectively.

Fig. 2 shows that the cell counts of yeast in doughs is the time required to reach the maximum consistency in min. increase with fermentation time. The yeast in the CK group S (stability) is the duration for which the dough consistency grew faster than in doughs with sourdough, and the cell counts remains at 500 BU. FQN is the farinograph quality number were higher than in doughs with sourdough. In addition, the recorded in the farinogram. The addition of the sourdough number of yeast cells reduced with an increase in the amount of resulted in a significant decrease (P < 0.05) in the water the sourdough in doughs, suggesting that the yeast growth might absorption, development time, stability, and farinograph quality be inhibited slightly by LAB. However, the remaining yeast cells number of dough compared with the CK sample. Moreover, were enough for dough fermentation. dough quality is influenced by the concentration of the added 3.2 Change of Total Titratable Acidity (TTA) and pH sourdough. These results are consistent with those reported by Kim et al.[1] and Wu et al.[2]. Arendt et al.[7] reported that As expected, the prolonged fermentation time led to an the lower pH of dough reduces the development time[7]. It increase in acidimetric characteristics (Fig. 3). After 12 h of is widely accepted that the changes in rheological properties fermentation, the TTA and pH of CK sample were 4.25 and 6.24, of doughs fermented with sourdough starters, which include a respectively. The doughs with 10%, 20%, 30%, and 40% of dynamic and complex system, are attributed to a wide range the sourdough showed significant increases (P < 0.05) in the of metabolites produced during the fermentation and not only TTA values compared to the CK sample. The TTAs of SCM-1, a result of simple pH decrease. As anticipated, the content SCM-2, SCM-3, and SCM-4 samples are 5.75 ± 0.32, 6.32 ± and composition of protein, in particular, the protein 0.28, 6.66 ± 0.35, and 7.21 ± 0.41, respectively. In contrast, the was the primary factor that impacted dough quality[18]. The pH values of these samples decreased significantly (pH = 5.06, wheat proteins hydrolysis due to sourdough fermentation weaken 4.78, 4.45, and 4.02) (P < 0.01) compare with that of the CK the strength of wheat dough and resulted in changes of the sample. The growth of LAB in sourdough resulted in doughs characteristics of dough quality. acidification during fermentation[14]. The higher acidity could 3.4 Effect of Sourdough on Steamed Bread Quality negatively affect the bread quality since it could cause off-flavor and reduce loaf volume, as well as diminish the crumb softness The influence of sourdough at various levels on the quality suitable for optimal wheat bread preparation[15]. The presence of of steamed bread is shown in Table2. The addition of sourdough sourdough could promote additional metabolic activity, thereby improved steamed bread quality, including improvements in increasing the production of lactate, acetate, and ethanol[16-17] sensory scores and specific volume, and decrease of the crumb and also contribute to the improvement of flavor, texture, and firmness, producing a lower spread ratio with an increase shelf life of bread. in the sourdough concentration up to 30% (SCM-3). Using 3.3 Dough Quality 30% sourdough, the highest sensory score and specific volume increased up to 25% and 26.7%, respectively. The crumb The main parameters recorded in farinogram, WA, DT, S, firmness decreased by up to 13.6% with the addition of 30% and FQN, are presented in Table1. WA means water absorption of sourdough compared with the CK sample. Moreover, a or the percentage of water required to yield a dough consistency significant decrease (P < 0.05) in the spread ratio was observed. of 500 Brabender units (BU). DT (dough development time) These results are similar to those reported by Dal Bello et al.[19] 88 Grain & Oil Science and Technology 2018, 1(2): 85-90 and Wu et al.[1], according to whom bread samples with higher Fig. 4 presents the moisture content of steamed bread crumb specific volumes had a softer crumb texture. Overall, the during its storage at various levels of sourdough. The remnant improvement on steamed bread quality owing to the sourdough moisture content in steamed bread crumb showed a decreasing is significant. trend during storage for 72 h in case of all the samples. Storage 3.5 Change of Steamed Bread Quality during Storage resulted in a significant decrease (P < 0.05) in moisture content of the CK sample, whereas the effect of storage time on the 3.5.1 Moisture Content moisture content of SCM-3 sample is not significant compared The loss in the quality of flavor and texture during storage to the CK sample. The LAB in the sourdough produces a is generally considered as the staling of cereal foods. Upon number of metabolites, such as exopolysaccharides (EPS) and/or storage, the crumb firmness increases significantly, and the enzymes, which have been shown to have a positive effect loaf volume loses its fragrance, assuming a stale flavor. These on texture and staling of bread. The EPS can improve the complex physical and chemical phenomena is a consequence viscoelastic properties of dough, increase loaf volume, reduce [12, 22] of starch granules gelatinized retrogradation during and crumb hardness, and prolong shelf life . The results of the steaming process, interchange of moisture between starch and present study suggest that 30% sourdough is enough to reduce protein constituents of the cereal foods, increase in the interaction the moisture redistribution inside crumb and hence mitigate the between protein fraction and starch, redistribution of water in reduction of moisture content of crumb over time. The addition foods, and removal of aromatic molecules[20-21]. The remnant of 10% and 20% of sourdough (SCM-1 and SCM-2) has no moisture content in steamed bread crumb reflects freshness. protective effect on steamed bread, perhaps due to lower quantity of EPS.

45 8 8 CK pH SCM-1 7 TTA 7 SCM-2 40 SCM-3 6 6 SCM-4

35 5 5

4 4

pH 30 TTA (mL) TTA 3 3

2 2 25 Moisture content (g/100g) 1 1 20 0 12 24 36 48 60 72 0 0 CK SCM-1 SCM-2 SCM-3 SCM-4 Storage time (h) Fig. 3 Variations of doughs with different sourdough Fig. 4 Moisture content of steamed bread crumb during concentrations in pH and TTA over 12 h fermentation storage at various levels of sourdough Data is reported as the average values of four replications (n = 4).

Table 1 Effect of sourdough addition on dough quality Sample WA (%) DT (min) S (min) FQN (mm) CK 61.9a 4.5a 4.2a 72a SCM-1 60.3b 3.2b 3.6b 68b SCM-2 58.5b 2.9b 3.2b 65b SCM-3 57.1bc 2.5b 2.9bc 64b SCM-4 56.8bc 1.9b 2.2b 61b Note: Mean values (n = 4) with different letters in the same column is significantly different at P < 0.05. WA, water absorption; DT, development time; ST, stability; FQN, farinograph quality number.

Table 2 Effect of sourdough at various levels on the quality of steamed bread Sample Score Specficvolume (mL/g) Crumb firmness (gf) Spread ratio (W/H) CK 76a 2.02a 1523.6a 1.52a SCM-1 81a 2.12a 1487.9b 1.47a SCM-2 86b 2.34b 1402.3b 1.42b SCM-3 95b 2.56b 1316.2b 1.38b SCM-4 89b 2.32b 1340.7b 1.44ab Note: Mean values (n = 4) with different letters in the same column are significantly different at P < 0.05. CHEN D, et al. Effects of Sourdough Addition on the Quality and Shelf Life of Chinese Steamed Bread 89

Table 3 Change in steamed bread texture during its storage for 3 days Sample Hardness (g) Chewiness Cohesiveness Springiness Resilience CK 0 232.5a 198.6a 0.721a 0.923a 0.512a 1 276.9A 267.2A 0.719a 0.921a 0.501A 2 356.4g 456.1g 0.687b 0.892b 0.428g 3 392.1G 598.6G 0.643b 0.875b 0.341G SCM-1 0 225.9b 187.2b 0.729a 0.928a 0.523b 1 256.2B 231.9B 0.723a 0.925a 0.512B 2 321.4h 298.6h 0.71b 0.918h 0.4687h 3 356.8H 398.7H 0.698b 0.903H 0.387H SCM-2 0 206.6c 176.5c 0.734a 0.931ac 0.535c 1 235.9C 198.2C 0.73a 0.927ac 0.538Cc 2 276.5i 267.8i 0.725a 0.92ih 0.512i 3 298.1I 351.4I 0.706b 0.915i 0.467I SCM-3 0 178.4d 165.5d 0.741a 0.936a 0.558d 1 198.5D 187.3D 0.737a 0.934a 0.549d 2 213.9j 234.1j 0.729a 0.931a 0.541jd 3 246.7J 308.2J 0.726a 0.925i 0.503J SCM-4 0 170.7e 173.9e 0.735a 0.929a 0.541ce 1 198.2E 198.6C 0.73a 0.924a 0.512B 2 234.6k 257.8k 0.723a 0.918ih 0.498k 3 256.9K 342.5I 0.714b 0.91i 0.452K Note: Mean values (n = 3) with different letters in the same column are significantly different at P < 0.05.

3.5.2 Texture Characteristics 4 Conclusions As a key sensory characteristic of cereal foods, texture is The addition of sourdough into Chinese steamed bread considered important for food manufacturers in order to meet resultes in a decrease of pH, an increase of TTA, and changes of consumer requirements in terms of the perceived product quality. dough quality characteristics. Sourdough has a positive effect Table3 illustrates the texture characteristics of steamed bread on sensory scores and specific volume of steamed bread, and a during its storage for 3 days derived by means of texture profile negative effect on crumb firmness; it produces lower spread ratio analysis (TPA). A distinct change in the textural characteristics with an increase in sourdough concentration up to 30% (SCM-3). of all samples over the storage period examined is apparent The shelf life study highlights that the addition of sourdough from the data in Table3. The hardness and chewiness of all has a positive impact on steamed bread quality during storage. the samples significantly increased with the storage time, whilst Addition of sourdough resultes in a slower loss of steamed the cohesiveness, springiness, and crumb resilience decreased bread crumb moisture content comparing with the CK samples significantly. The hardness and chewiness of SCM-1, SCM-2, during storage. According to the results of TPA, hardness and and SCM-3 were found to be lower than those of the CK sample chewiness of all samples significantly increased with storage for the same duration of storage. Moreover, cohesiveness, time, whilst cohesiveness, springiness, and crumb resilience springiness, and crumb resilience of SCM-1, SCM-2, and decreased significantly. Hardness and chewiness of SCM-1, SCM-3 were found to be higher than those of the CK sample. SCM-2, and SCM-3 were lower than those of CK for the same All the changes observed in TPA are considered to have a duration of storage. Moreover, cohesiveness, springiness, and negative impact on the steamed bread quality of this type, e.g., crumb resilience of SCM-1, SCM-2, and SCM-3 were found the crumb becomes harder (increased hardness) and requires to be higher than those of the CK samples. This indicates that more energy to disintegrate and a longer time for mastication the addition of sourdough improves steamed bread quality and (increased chewiness)[23]. This indicates that the addition of delayes the staling speed during storage. Moreover, addition sourdough improves the quality and delays the staling speed of 30% sourdough resultes in the best protective effect on of steamed bread during its storage. Meanwhile, steamed steamed bread staling, thus confirming the effect of sourdough bread containing 30% sourdough (SCM-3) maintaining superior concentration on steamed bread quality. texture characteristics compared to CK, SCM-1, SCM-2, and SCM-4 over the storage period investigated. SCM-3 maintained Conflict of Interest a softer crumb than three other samples throughout the storage The authors declare that there is no conflict of interest. period, although this is not significant in all cases. A trend towards lower crumb chewiness values (Table2) was noted of References SCM-3 similar to the trend observed of crumb hardness. The [1] WU C, LIU R S, HUANG W N, et al. Effect of sourdough loss of resilience (ability of crumb to recover from compression) fermentation on the quality of Chinese Northern-style steamed was found to be similar in CK and samples with sourdough, but [J]. Journal of Cereal Science, 2012, 56(2): 127-133. the extent of loss was the greatest in CK. [2] KIM Y S, HUANG W N, ZHU H Y, et al. Spontaneous sourdough processing of Chinese Northern-style steamed breads and their 90 Grain & Oil Science and Technology 2018, 1(2): 85-90

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