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Effect of water-soluble dietary fiber resistant dextrin on flour and bread qualities
Food Chemistry 317 (2020) 126452
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Effect of water-soluble dietary fiber resistant dextrin on flour and bread qualities
T
Zheng Huanga,1, Jing Jing Wanga,c,1, Yu Chend, Na Weid, Yi Houb, Weidong Baie, Song-Qing Hua,
⁎
a
Overseas Expertise Introduction Center for Discipline Innovation of Food Nutrition and Human Health (111 Center), School of Food Science and Engineering, South China University of Technology, Guangzhou 510640, China b State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou, Guangdong 510640, China c Department of Food Science and Technology, Foshan University, Foshan 528000, China d Guangdong Food Industry Research Institute Co Ltd, Guangzhou 511400, China e College of Food Science and Technology, Zhongkai University of Agriculture and Engineering, Guangzhou 510225, China
ARTICLE INFO
ABSTRACT
Keywords: Water-soluble resistant dextrin Wheat dough Bread Processing quality Digestion resistibility
A new water-soluble resistant dextrin (WSRD), fabricated by thermal-acid treatment following amylase hydrolysis from corn starch, was expected to strengthen the dietary fibers intake of flour products. This study was to investigate the effects of WSRD on flour processing quality, and further dissect its improvement mechanisms by farinographic and rheological analysis, SDS-PAGE, Fourier transform infrared spectroscopy, texture analyzer, etc. Results showed that WSRD greatly improved the viscoelasticity and strength of dough, which was predominantly contributed by its formation of gel-like networks. Meanwhile, the WSRD-induced increase of gluten aggregates and β-sheet conformation provided the structural basis for enhancing dough quality. Notably, WSRD greatly promoted the sensory appearance and crumb quality of baked breads. Moreover, the WSRD-treated breads resisted the hydrolysis of digestive fluid and enzymes. Therefore, WSRD can strengthen the processing qualities and nutritional values of flour products, which will broaden the application of the novel dietary fiber in flour industry.
1. Introduction Dietary fibers have received particular concern in recent years as they aren’t enzymatically degraded within the human alimentary digestive tract (Brennan & Cleary, 2007). Moreover, the dietary fibers intake is advocated in the nutrition recommendations of several European countries, which promotes the development of grain-rich food as cereal products are the main source of dietary fibers (Wang, Rosell, & Barber, 2002). Therefore, the development of staple foods enriched with fibers is an important contribution to a broader supply of food products with beneficial health effect. As a popular staple food material, wheat flour is used to produce numerous foods such as bread and pasta, and hence it is an ideal candidate to be added with dietary fiber for the nutrient enhancement. Besides the nutritional quality, the dietary fibers inevitably affect the flour processing quality, including the qualities of dough development, texture and baked properties of flour products. Previous studies reported that the addition of dietary fibers usually resulted in a physical
interfering effect and water competition between fibers and gluten (Bock & Damodaran, 2013), which collectively weakened the glutenin network and redistributed the water molecules in the system. Recently, few kinds of dietary fibers are reported to bring positive effects on flour processing quality. Water-soluble resistant dextrin (WSRD) prepared by starch is a new kind of low molecular weight dietary fiber with good solubility (Wang, Kozlowski, & Delgado, 2001), which has been announced as an ordinary food (Zhang et al., 2017). Besides various physiological functions, WSRD has excellent processing performance characterized by its great resistance to acid, alkali and high temperature (Barczynska, Jochym, Slizewska, Kapusniak, & Libudzisz, 2010). WSRD has been widely used in developing low calorie-food (Serpelloni, 2004; Serpelloni, 2007). Lin and Lee (2005) replaced sucrose with commercial resistant dextrin Fibersol-2 to prepare chiffon cakes. Low replacement (< 50%, w/w) of sucrose didn’t significantly affect the sensory characteristics and overall liking of cakes, while high replacement (60%, 80%, w/w) led to the baked cakes with a lower volume, greater
Corresponding author at: Overseas Expertise Introduction Center for Discipline Innovation of Food Nutrition and Human Health (111 Center), School of Food Sciences and Engineering, South China University of Technology, Guangzhou 510641, China. E-mail address: [email protected] (S.-Q. Hu). 1 Z. Huang and J.J. Wang contributed equally to this work. ⁎
https://doi.org/10.1016/j.foodchem.2020.126452 Received 1 August 2019; Received in revised form 18 February 2020; Accepted 18 February 2020 Available online 19 February 2020 0308-8146/ © 2020 Elsevier Ltd. All rights reserved.
Food Chemistry 317 (2020) 126452
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hardness, and lower degree of overall liking. Miyazaki, Maeda, and Morita (2004) found that the low substitution (2.5%, w/w) of conventional dextrin didn’t significantly influence the viscoelasticity of dough, but high substitution (7.5%, w/w) caused poor dough properties and bread quality. Therefore, exploiting new WSRD to enrich and compensate the functions of conventional dextrin is distinctly necessary for low calorie-food industry. In this study, the water-soluble WSRD was fabricated by thermalacid treatment following amylase hydrolysis using corn starch as raw material and food grade paraffin as heat transfer medium. More importantly, the WSRD was added to the flour and expected to not only increase the dietary fiber content of the flour products, but also improve their processing quality. Therefore, the objectives of this study were to qualitatively investigate the effects of different WSRD substitution levels on flour processing quality, and further dissect the related function mechanisms of WSRD. The generated knowledge may offer new opportunities to broaden the application of the novel dietary fiber and provide a kind of healthy and functional ingredient for flour industry.
2.3. Determination of molecular weight distribution of the dextrins The molecular weight distribution of dextrin was determined by gel permeation chromatography in a Waters system comprising a 1525 high-performance liquid chromatography (HPLC) pump with a 717 plus auto sampler and a 2414 refractive index (RI) detector (Waters, America). Dextrin was dissolved in mobile phase (KH2PO4, 0.02 mol/ ml) to obtain the injected concentration of 2 mg/ml. The sample solution was filtered through a membrane filter (0.45 µm). A TSK G5000PWXL column filled with hydrophilic spherical polymethacrylate particles (4 kDa–800 kDa, 7.8 × 300 mm) and a TSK G-3000PWXL column (< 40 kDa, 7.8 × 300 mm) (TOSOH, Japan) was used for the analysis of fractions with a flow rate of 0.6 ml/min. The injected volume was 10 µl and the column temperature was 25 °C. Eight standard dextrins with different molecular weights (2 kDa–800 kDa) were used. The weight-average molecular weight (Mw) was calculated based on the calibration curve. The percentage of particular fractions detected in the chromatograms was calculated using Breeze HPLC Systems (Version 3.3, America) (Wang, Liu, & Qin, 2017; Han et al., 2011).
2. Materials and methods
2.4. In vitro hydrolysis rate of WSRD and bread
2.1. Materials
Anti-digestion of WSRD in simulated gastric fluid (SGF) was determined by the method as follows. The SGF was freshly prepared according to the U.S. Pharmacopoeia (The United States Pharmacopoeia Inc., 2000). Briefly, 3.2 g pepsin and 2.0 g NaCl were dissolved in 1000 ml water and equally divided into three portions, and each pH was adjusted by hydrochloric acid (1.0–3.0). WSRD was dissolved in each SGF with a final concentration of 1% and then digested at 37 ℃ for 5 h. Samples (0.2 ml) from each SGF were collected per 1 h and transferred to tubes containing 0.8 ml distilled water and 1 ml of 3,5 dinitrosalicylic acid (DNS). Tubes were incubated for 10 min at 100 ℃ water bath. Afterwards, 15 ml of distilled water was added to each tube and mixed thoroughly. The released reducing sugar was measured in parallel with the standard curve at 530 nm. In vitro hydrolysis rate of WSRD and bread in simulated intestinal fluid (SIF) were measured according to the method reported by Ovando-Martinez, Sáyago-Ayerdi, Agama-Acevedo, Goñi, and BelloPérez (2009). Briefly, phosphate buffer (pH 7.0) was prepared and equally divided into several portions (50 ml/portion) and each pH (pH 6.0–8.0 for WSRD hydrolysis; pH 7.0 for bread hydrolysis) was adjusted. Pure WSRD or WSRD-treated breads were dissolved in SIF solutions (2%, w/v) and incubated at 37 ℃ for 5 min. Then, 1 ml of αamylase solution (40 mg/ml in DNS solution) was added to each sample to perform the digestion. After 5 h treatment, the hydrolysis rate was determined by DNS method.
Commercial ‘Xinle’ wheat flour (5.35% moisture, 12.50% protein, 0.70% fat and 75.70% carbohydrate, w/w, dry basis) was purchased from Saixin Flour Industry Co., Ltd. (Inner Mongolia, China). All reagents including α-amylase from Bacillus amyloliquefaciens (EC 3.2.1.1, 10–30 U/mg), α-glucosidase from Bacillus stearothermophilus (EC 3.2.1.20, ≥50 U/mg) and pepsin from porcine gastric mucosa (EC 3.4.23.1, ≥250 U/mg) were purchased from Sigma-Aldrich (St. Louis, MO, USA) unless otherwise specified. 2.2. WSRD and its fabrication processing WSRD was fabricated by the method of thermal-acid treatment following amylase hydrolysis from corn starch, which was based on the method reported by Laurentin, Cárdenas, Ruales, Pérez, and Tovar (2003) with some modifications using food grade paraffin as a novel heat transfer medium. 20 g of corn starch was sprayed with 1 ml 0.5% citric acid. After 0.5 h treatment, the samples were dried at 110 ℃ to reach < 5% moisture. Subsequently, the samples were crushed and sieved through a 60 μm mesh screen. Then, the samples were mixed with food-grade paraffin in a 1:1.2 ratio (w/w) and heated at 140 ℃–160 ℃ for 1.5 h to 2 h. After reaction, the mixture was immediately dissolved in distilled water to remove the paraffin to obtain crude dextrin solution. Refining processes including amylase hydrolysis, decolorization, desalting, concentrating and drying were carried out. In detail, the crude solution was adjusted to pH 7.0 and then reacted with 0.5% αamylase at 95 ℃ for 1 h. Afterwards, the temperature was cooled down to 60 ℃ and pH was adjusted to 5.0. The complex enzyme (α-amylase: α-glucosidase = 1:1) was added with a final concentration of 4.0% (w/ v) kept at 60 ℃ for 24 h, i.e. 200–600 U/mL α-amylase and ≥1000 U/ mL α-glucosidase were added into crude solution. Subsequently, the crude solution was heated to 90℃ to terminate the reaction and then filtrated. For decolorization, the filtrate was stirred with 20% activated carbon at 100 ℃ for 20 min. After filtration, the light yellow, clear and tasteless solution was obtained. The desalination treatment was performed using the ion exchange resin, and the final products were concentrated by rotary evaporator. The content of dietary fiber was analyzed according to the enzymatic-gravimetric AOAC official 991.43 method (AOAC, 2003). Meanwhile, the content of protein, fat, ash and moisture were measured according to Kjeldahl (AOAC method 955.04), Soxhlet (AOAC method 960.39) and dry ashing (AOAC method 923.03) and oven drying (AOAC method 977.11), respectively.
2.5. Micro-farinograph analysis and preparation of gluten samples Micro-farinograph measurements and the evaluation of farinogram were performed by AACC-approved methods (AACC, 2000). ‘Xinle’ wheat flour was mixed with different WSRD levels (Table 1) using a 4 g Mixograph (Perten Instrument, Sweden). Effects of WSRD levels (1%, 3%, 5%, 7%, 10%, w/w, flour base) on dough quality were investigated. Farinography parameters including water absorption (WA), dough development time (DDT), dough stability time (DST) and degree of softening index (DSI) were recorded. Five replicates were tested for each group. Dough and gluten samples were prepared based on Wang et al. (2016) and then wrapped with plastic wrap to prevent the loss of water, and then divided into three parts: the first part was used for rheological measurement; the second part was lyophilized to obtain freeze-dried dough; the third part was employed to obtain the freeze-dried gluten. The gluten was ground into powder and sieved through a 180 μm mesh screen, then stored at –20 °C for SDS-PAGE analysis. 2
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Table 1 Effect of resistant dextrin on farinogram parameters. WSRD level (%, w/w) Control 1 3 5 7 10
WA (%, w/w) 61.45 60.65 56.84 52.00 51.20 45.20
± ± ± ± ± ±
DDT (min) e
0.07 1.20d 0.42c 0.00b 1.56b 0.00a
2.60 2.03 3.47 4.20 4.90 4.25
± ± ± ± ± ±
DST (min) a
0.14 0.93a 0.42b 0.40b 0.14b 0.21c
DSI (FU) a
3.40 ± 0.28 3.63 ± 0.06a 4.88 ± 0.19b 6.33 ± 0.31c 7.60 ± 0.00d 17.15 ± 0.07e
144.90 ± 0.00c 153.23 ± 11.55d 133.27 ± 7.58c 105.00 ± 13.23b 87.50 ± 3.54b 45.00 ± 5.00a
Different letters in the same column indicate a significant difference (p < 0.05, n = 5).
2.6. Dynamic rheological determination.
2.11. Texture analysis and sensory evaluation of WSRD-treated bread
Rheological characterization of dough was based on Wang et al. (2016). The rheological behavior of dough was analyzed by a rheometer (AR1500ex, TA, USA). The linear viscoelastic region was determined by a frequency sweep test from 0.1 to 10 Hz with 0.1% deformation. Rheological parameters including storage modulus (G'), loss modulus (G''), complex modulus G* = G'2+G''2 and loss tangent (tan δ) were recorded.
The bread volume was determined by seed displacement method (Wang et al., 2002). Crumb texture was determined by a texture analyzer (TA-XT Plus, UK) equipped with a 25 mm diameter probe. Bread slices of 2 cm thickness were compressed to 40% of their original height. Three replicates were tested for each group. The sensory evaluation of fresh breads was performed according to the studies of Burešová, Masaříková, Hřivna, Kulhanová, and Bureš (2016) and Ho, Abdul Aziz, and Azahari (2013). In detail, 10 trained panelists from the major of food science and technology in South China University of Technology were invited. The sensory evaluation was carried out as follows: 6 groups of bread samples were prepared and randomly coded with the number from 1 to 6, respectively. And then, the panelists were asked to evaluate the sensory parameters of the bread samples, including volume, color, appearance, texture and taste according to the evaluation standard in Table S1. Before analyzing the results, the maximum and minimum scores for each group were removed and the remaining 8 scores were averaged as the final score.
2.7. Protein electrophoresis Protein solutions (20 μl, 20 mg/ml) were mixed with 5 μl loading buffer (62.5 mM Tris-HCl, 20% glycerol (v/v), 1% SDS (w/v), pH 6.8) for non-reducing SDS-PAGE. The discontinuous system consisted of separating gel (12%, pH 8.6) and stacking gel (5%, pH 6.8). The gel was stained with Coomassie Brilliant Blue (0.25% R-250, 45% methanol and 10% acetic acid) and de-stained in methanol and acetic acid solution (methanol/acetic acid/water = 1:1:8, v/v/v). The molecular weight of protein standard markers ranges from 14.4 kDa to 116 kDa.
2.12. Statistical analysis Values were shown in the means ± standard deviation of three replicate samples unless otherwise specified. One-way analysis of variance (ANOVA) was used to compare the value differences under different treatments (p < 0.05) by SPSS software (Version 17.0, SPSS Inc., USA).
2.8. Scanning electron microscopy (SEM) The microstructure of dough was observed by SEM (Evo 18, Carl Zeiss, Germany). The freeze-dried dough samples were fixed to the sample holder and sputter-coated with gold. Subsequently, the samples were transferred to the microscope and observed at 10.0 kV with a vacuum of 9 × 10−5 MPa.
3. Results and discussion 3.1. WSRD improved the digestion resistibility of bread 3.1.1. Digestion resistibility of WSRD in SGF and SIF The weight-average molecular weight (Mw) of the products from the treated corn starch was 3.89 kDa (Fig. S1) which was generally similar to the Mw of potato starch-based dextrin reported by Jochym, Kapusniak, Barczynska, and Śliżewska (2011) and Kapusniak, Kapusniak, Ptak, Barczynska, and Żarski (2014). Meanwhile, the generation of α-1,3-glucosidic bond, a typical covalent bond indicator of dextrin, was determined (Fig. S2) during the dextrinization of corn starch. The composition analysis showed that the products contained high dietary fiber reaching 83.40 ± 1.16%, 0.50 ± 0.03% protein, 0.34 ± 0.02% fat, 0.05 ± 0.01% ash and 4.40 ± 0.78% moisture. Furthermore, the product presented good water-solubility for its watersolution at 1% (w/v) or 10% (w/v) concentration was transparent and no precipitation appeared (Fig. S3). Therefore, all these results indicated that the raw corn starch was completely degraded to watersoluble resistant dextrin (WSRD). The prominent feature of WSRD is resisting the hydrolysis of human digestive fluid and enzymes (Guerin-Deremaux et al., 2011). In Fig. 1A, the hydrolysis degree of WSRD in SGF increased with the pH decreasing from 3.0 to 1.0 under the same treatment time. At each given pH, the hydrolysis degree of WSRD slightly increased with the treatment time increasing, and almost reached the plateau after 4 h. However, the
2.9. Fourier transform infrared spectroscopy (FT-IR) The FT-IR spectra were determined by a Bruker Vertex-70 spectrometer (Bruker Optics, Ettlingen, Germany). The gluten samples were mixed with KBr and then a total of 64 scans from 400 to 4000 cm−1 against the background were taken at 4 cm−1 resolution. The curvefitting and peak area corresponding to the different secondary structures were obtained using PeakFit version 4.12 software (Wang et al., 2016). 2.10. Breadmaking procedure The breadmaking procedure was performed according to Liu et al. (2017). The bread formula was consisted of 100 g WSRD substituted wheat flour, 3 g vegetable oil, 3 g pure milk, 3 g NaCl, 5 g sucrose, 1 g dry yeast (Angle Brand, China) and the corresponding water determined by farinograph. All raw materials were mixed using an automatic machine and the dough was divided into three pieces (45 g/ piece). After proofing at 35 °C for 90 min, the dough was baked at 190 °C for 10 min. Loaves were taken out and cooled down for 1 h before texture analysis. 3
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Fig. 1. Hydrolysis degree of WSRD in simulated gastric fluid (A), simulated intestinal fluid (B) and WSRD-treated bread in simulated gastric fluid (C).
significantly influenced by WSRD (Table 1). With WSRD levels ranging from 1% to 10%, the WA was significantly (p < 0.05) decreased from 60.65% to 45.20%, which was obviously lower than control (61.45%). The decreased WA was probably due to that the added WSRD diluted the glutenin and hence weakened the formation of gluten networks (Miyazaki et al., 2004; Wang et al., 2016), because glutenin especially its formed networks played an important role in absorbing and retaining water (Wang et al., 2016; Chen et al., 2019). Such facts were supported by Zhou et al. (2014), reporting that the diluted glutenin impeded the massive formation and the swelling of gluten network. For DDT, WSRD substitution greatly (p < 0.05) elevated its values from 2.03 min to 4.90 min, indicating that WSRD delayed the formation of gluten matrix. DST reflecting the resistance of the dough against the blades is another key indicator for flour processing quality. Compared with control (3.40 min) (Table 1), the DST of WSRD-treated dough was markedly increased from 3.63 min at 1% level to 17.15 min at 10% level, indicating that WSRD improved the flour processing quality. The massive formation of strengthened gluten networks is responsible for the improvement of farinogram parameters (Wang et al., 2016). In this study, the WSRD substitution should weaken and delay the formation of gluten networks from WA and DDT results. However, the DST results implied that the WSRD-treated dough exhibited an excellent resistance against the shear stress. Therefore, it was inferred that an unknown structures or components inside the dough enhanced the processing quality of flour.
highest hydrolysis degree didn’t exceed 1.5%, indicating that WSRD was difficult to be hydrolyzed in SGF. Compared to SGF, SIF-treated changes in hydrolysis degree of WSRD presented opposite trends with the alteration of pH (Fig. 1B). Under the same time, the hydrolysis degree of WSRD in SIF increased with the pH increasing from 6.0 to 8.0. With the increase of time, all hydrolysis degrees exhibited a slight increase but didn’t exceed 4.0% at each pH, also suggesting that WSRD was difficult to be hydrolyzed in SIF. The digestion resistibility of WSRD to SGF and SIF was greatly attributed to the generation of α-1,2- and α-1,3-glucosidic bonds at the expense of α-1,4- and α-1,6-glycosidic bonds during dextrinization of corn starch. It is well known that the human digestive enzymes (mainly α-amylase) mostly take α-1,4- and α-1,6-glycosidic bonds as hydrolysis targets, while the formation of new α-1,2- and α-1,3-glucosidic bonds (Fig. S2) makes dextrin less susceptible to the digestive enzymes (Jochym & Nebesny, 2017). 3.1.2. Digestion resistibility of WSRD-treated bread In Fig. 1C, the hydrolysis degree of bread without WSRD was 92.1%. As WSRD levels increased from 1% to 10%, the hydrolysis of bread significantly (p < 0.05) decreased from 91.8% to 84.5%. Therefore, WSRD improved the digestion resistibility of bread, especially when the WSRD levels reached 7% and 10%. During WSRD preparation, those easily digested glycoside bonds have been cleaved and destroyed by enzymes and acid-heat treatment. Meanwhile, some branched structures which were difficult to be hydrolyzed newly formed. Therefore, WSRD could resist the hydrolysis of most human digestive enzymes, resulting in a mild glycemic response. Consequently, WSRD will be the potential ingredients of special foods for people with diabetes. Meanwhile, WSRD is also expected to help people with over-weight and cardiovascular disease (Guerin-Deremaux et al., 2011).
3.2.2. Effects of WSRD on the rheological properties of dough The rheological properties of WSRD-treated dough are shown in Fig. 2. In Fig. 2A and B, the G' and G'' of all samples increased with the frequency increasing, and the G' was higher than G''. Meanwhile, all tan δ values were less than 1 (Fig. 2D), meaning that the G' of all samples were more prominent. According to Demirkesen, Mert, Sumnu, and Sahin (2010), such phenomenon indicated that the WSRD-treated dough had a weak gel behavior or solid like structure. In detail, when the frequency was lower than 5 Hz, the WSRDtreated dough presented an overall decrease in G' with its substitution levels increasing from 1% to 10%, suggesting that the gel networks
3.2. WSRD improved flour processing quality 3.2.1. Effects of WSRD on the farinographic properties of dough Compared with control, the WA, DDT, DST and DSI of dough were 4
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Fig. 2. Effects of WSRD on the rheological properties of dough. (A) elastic moduli (G′); (B) viscous moduli (G″); (C) complex moduli (G*); (D) loss tangent (tan δ).
Fig. 3. Effects of WSRD on microstructures of dough. (A) Control dough; (B) 1% WSRD-treated dough; (C) 3% WSRD-treated dough; (D) 5% WSRD-treated dough; (E), (G) 7% WSRD-treated dough; (F), (H) 10% WSRD-treated dough.
Fig. 4. Photos of bread (A) and slices (B) made from the WSRD-treated dough.
5
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Table 2 Effects of WSRD on the qualities of bread prepared by medium-gluten flour. WSRD (%, w/w) Control 1 3 5 7 10
SV (×10−3 m3/kg) 6.69 6.59 7.71 7.61 8.07 6.54
± ± ± ± ± ±
a
0.14 0.26a 0.07b 0.14b 0.03c 0.40a
Hardness (×10−3 kg) 1775.12 1520.45 2290.85 2016.80 1535.12 1456.04
± ± ± ± ± ±
Chewiness (×10−3 kg)
b
46.77 22.29a 78.44d 140.68c 54.10a 0.00a
1540.10 1284.42 1873.97 1610.07 1272.28 1120.76
± ± ± ± ± ±
c
32.86 12.05b 40.83d 121.88c 12.81b 0.00a
Springiness 0.87 1.00 1.00 1.00 1.00 1.00
± ± ± ± ± ±
Cohesiveness a
0.04 0.01a 0.00a 0.00a 0.01a 0.00a
0.87 0.85 0.82 0.80 0.83 0.77
± ± ± ± ± ±
0.04b 0.01b 0.01a 0.00a 0.04b 0.00a
SV: specific loaf volume; Letters within a column indicate significantly different values (p < 0.05, n = 3).
proteins (HMMP, > 97 kDa) were extracted from WSRD-treated dough. As the amount of WSRD increased, the band intensity (red box) of HMMP gradually increased, suggesting that WSRD improved the HMMP formation. The amounts of glutenin polymers, particularly high molecular weight polymers, were positively correlated with dough strength (Wang et al., 2016). Therefore, the results supported that WSRD enhanced the dough strength from rheological results (Fig. 2C). Changes in secondary structures of gluten are related to the dough development (Mejia, Mauer, & Hamaker, 2007). In Table S3, the βsheet structure was the dominant component in all WSRD-treated gluten, which was consistent with the report of Wang et al. (2015). Compared with the control, the proportion of β-sheet structure gradually increased from 50.3% to 54.6% as the WSRD increased from 1% to 10%. During the dough development, the increase in β-sheet was an indicator of high molecular aggregates formation (Wang et al., 2016), which was reflected by SDS-PAGE analysis (Fig. S4). More importantly, such results confirmed the functional characteristics of WSRD from a structural level. However, the proportion of β-turn structure decreased from 26.3% to 21.8%, and the significant changes in α-helix and random coils weren’t observed. In conclusion, the addition of WSRD favored the transition of β-turn to β-sheet. Such behavior can be reasonably explained by the widely accepted “Loop and Train” model of dough. The model proposes that the “train” region is associated with β-sheets while the “loop” with extended hydrated β-turns. The dough system gets plasticized allowing β-turns in adjacent β-spirals to form interchain β-sheets with the water content increasing. Further hydration breaks some interchain H bonds between glutamine residues leading to the formation of loops consisting of βturns (Shewry, Popineau, Lafiandra, & Belton, 2001). In control, the dough got sufficient water, so the gluten proteins formed the “loop” where protein–water–protein interactions formed. When WSRD was added, the mobility of the hydrated segments would be reduced, owing to the water competition between protein and WSRD. Consequently, WSRD increased the intermolecular contacts and binding sites for H bonding to form extended β-sheet in dough. Similar results have been reported by Sivam, Sun-Waterhouse, Perera, and Waterhouse (2013), showing that pectin and polyphenols-treated breads gained more βsheet conformation at the expense of β-turn. Another study of Nawrocka, Szymańska-Chargot, Miś, Wilczewska, and Markiewicz (2017) also reported that the cooperation of inulin with gluten formed more β-sheet at the expense of β-turn.
were elastic but weak. However, the WSRD-treated dough possessed an increased G' during 5 Hz to 10 Hz, implying the gel networks became stronger (Wang et al., 2019). Interestingly, 3% WSRD-treated dough presented different changes in rheological parameters, which needs future investigation. Additionally, G* was employed to characterize the stiffness of dough. Changes in G* showed a similar trend with G′ (Fig. 2C), implying that WSRD strengthened the stiffness of dough. Bread quality is directly related to the gluten structures which form continuous and viscoelastic networks in dough. Previous studies revealed that the viscoelasticity of dough was associated with glutenin, because glutenin macropolymers (GMP) were the main components that held the gluten networks together (Anjum et al., 2007). In theory, the WSRD substitution inevitably reduced the GMP content owing to the dilution of glutenin, which should negatively affect the rheological properties of dough. However, WSRD finally improved the formation of gluten networks and enhanced the stiffness of dough (Fig. 2). Therefore, these results further supported that there was an unknown structures or components from WSRD substitution compensating the negative impacts of diluted glutenin. 3.2.3. Effects of WSRD substitution on the microstructure of dough The microstructures of wheat doughs with or without WSRD clearly displayed the gluten matrix (G), large starch granules (LS), small starch granules (SS) and the formed gel-like network structures (GNS) on the gluten matrix (Fig. 3). In Fig. 3A, control samples showed the typical microstructure of dough in which starch granules were wrapped in gluten proteins to support the gluten matrix (Correa, Anon, Perez, & Ferrero, 2010). In 1% and 3% WSRD-treated dough (Fig. 3B and C), some filamentous and thin lamellar gel-like structures were observed. When WSRD reached 5% and 7%, the gel network structures became much obvious (Fig. 3D and E). Further elevating WSRD to 10% (Fig. 3F), the network structures became relatively continuous, suggesting the formation of a new network. At higher (1500×) magnifications, similar structures could still be found, and the cross-linked structures were more visible (Fig. 3G and H). Considering above analysis, the unknown structure or component was none other than this gel network structure formed by WSRD enhancing the processing quality of flour. Various water-soluble dietary fibers are capable of forming gels, and their aqueous solutions usually possess viscosity or adhesiveness. To verify this point, the viscosity and adhesiveness of 50% WSRD aqueous solution (w/v) were determined (Table S2). Results showed that the values of viscosity and adhesiveness of WSRD solutions could be highly comparable to the commercial liquid glue (Deli Brand, No.7303, China). Additionally, similar gel-like network structures have been mentioned in other studies (Sudha, Vetrimani, & Leelavathi, 2007; Ho et al., 2013). For example, Linlaud, Puppo, and Ferrero (2009) found that more elastic networks formed in dough in the presence of xanthan and guar gum. Therefore, the gel network structures were firmly believed to be constructed by the WSRD after hydration, which in turn enhanced the farinographic (Table 1) and rheological properties of dough (Fig. 2).
3.3. WSRD-substitution improved the quality of baked bread 3.3.1. Morphology of WSRD-treated bread Overall speaking, the surface of WSRD-treated bread gradually became smoother as the WSRD level increased (Fig. 4A). An obvious crevice structure appeared on the surface of control and 1% WSRDtreated breads. The crevices were gradually seamed with the WSRD levels ranging from 3% to 7%, and even disappeared at 10% WSRD level. Volume analysis showed that the control, 1% or 10% WSRD-treated breads almost had the same volume (Table 2). When 3%–7% WSRD was added, the bread volume significantly increased, and reached the
3.2.4. Effects of WSRD on the gluten aggregates and structures SDS-PAGE was carried out to understand the effects of WSRD on the gluten aggregates formation (Fig. S4). SDS-soluble high molecular mass 6
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maximum 8.07× 10−3 m3/kg at 7% WSRD substitution. Changes in the bread volume were consistent with the pore distribution in crumb, because there were sporadic and unevenly distributed pores in the control, 1% and 10% WSRD-treated breads, while even and dense pores were spread in 3%, 5% or 7% WSRD-treated samples (Fig. 4B). It has been clarified that the gluten networks have high availability to retain the carbon dioxide produced by yeast during proofing and baking, which determines the loaf volume and crumb structure (Liu et al., 2018). Meanwhile, a good paste must retain sufficient viscosity to prevent the incorporated air bubbles being lost during heating (Zhang, Zhang, Wang, Qian, & Qi, 2015). In this study, the WSRD formed the gel network structures (Fig. 3) and enhanced the viscoelasticity and stiffness of dough (Fig. 2), which greatly contributed to the bread quality. However, the excessive addition of WSRD led to the deterioration of bread volume, mainly due to that an overly strong gel network limited the expansion of dough during fermentation and baking (Liu et al., 2018).
the sensory appearance and crumb quality of baked breads. Moreover, WSRD-treated breads could resist the hydrolysis of digestive fluid and human digestive enzymes as expected. Therefore, the WSRD has the potential to be a healthy and functional ingredient used in wheat flour products for enhancing their processing qualities and nutritional values. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This research was supported by the National Natural Science Foundation of China (grant numbers 31771906), Science and Technology Planning Project of Guangzhou City, China (grant number 201604020032), Science and Technology Planning Project of Shaoguan City, China (grant number Shaoke-2017-62), and the 111 project (grant number B17018). Jing Jing Wang is grateful to the financial support from Shanghai Ocean University Funding (A2-2006-00-200364 and A22006-00-574200221).
3.3.2. Effects of WSRD on the bread texture Texture of WSRD-treated breads crumb was further analyzed by TPA. Compared with control, the hardness of 1%, 7% and 10% WSRDtreated breads significantly decreased, while 3% and 5% WSRD-treated samples obviously increased, and the maximum hardness reached 2290.85 g at 3% WSRD levels (Table 2). Crumb chewiness reflects the energy required to masticate food to a state ready for swallowing (García-Segovia, Pagán-Moreno, Lara, & Martínez-Monzó, 2017). The chewiness parameters presented a similar change with the hardness values, that’s to say, relatively lower WSRD substitution (3%, 5%) markedly improved the bread chewiness, while higher WSRD (7%, 10%) obviously decreased the chewiness. Based on the study of Bourne and Malcolm (2003), the bread with appropriate WSRD level tended to remain in the mouth without rapidly breaking up or dissolving. Significant changes in springiness and cohesiveness were not observed for all WSRD-treated samples. All results implied that the WSRD did possess the ability to strengthen the processing quality of medium-gluten flour.
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.foodchem.2020.126452. References AACC (2000). Approved methods of the American association of cereal chemists. St. Paul MN: The Association. Anjum, F. M., Khan, M. R., Din, A., Saeed, M., Pasha, I., & Arshad, M. U. (2007). Wheat gluten: high molecular weight glutenin subunits–structure, genetics, and relation to dough elasticity. Journal of Food Science, 72(3), R56–R63. AOAC (2003). Total, soluble and insoluble dietary fibre in foods and food products, enzymatic-gravimetric method. In Horwitz, W. (ed.) Official methods of analysis of AOAC International. Barczynska, R., Jochym, K., Slizewska, K., Kapusniak, J., & Libudzisz, Z. (2010). The effect of citric acid-modified enzyme-resistant dextrin on growth and metabolism of selected strains of probiotic and other intestinal bacteria. Journal of Functional Foods, 2(2), 126–133. Bock, J. E., & Damodaran, S. (2013). Bran-induced changes in water structure and gluten conformation in model gluten dough studied by fourier transform infrared spectroscopy. Food Hydrocolloids, 31(2), 146–155. Bourne, M. C., & Malcolm, C. (2003). Food texture and viscosity: concept and measurement. International Journal of Food Science & Technology, 38(7), 839–840. Brennan, C. S., & Cleary, L. J. (2007). Utilisation glucagel in the β-glucan enrichment of breads: A physicochemical and nutritional evaluation. Food Research International, 40(2), 291–296. Burešová, I., Masaříková, L., Hřivna, L., Kulhanová, S., & Bureš, D. (2016). The comparison of the effect of sodium caseinate, calcium caseinate, carboxymethyl cellulose and xanthan gum on rice-buckwheat dough rheological characteristics and textural and sensory quality of bread. LWT – Food Science and Technology, 68, 659–666. Chen, M., Wang, L., Qian, H. F., Zhang, H., Li, Y., Wu, G. C., et al. (2019). The effects of phosphate salts on the pasting, mixing and noodle-making performance of wheat flour. Food Chemistry, 283, 353–358. Correa, M. J., Anon, M. C., Perez, G. T., & Ferrero, C. (2010). Effect of modified celluloses on dough rheology and microstructure. Food Research International, 43(3), 780–787. Demirkesen, I., Mert, B., Sumnu, G., & Sahin, S. (2010). Utilization of chestnut flour in gluten-free bread formulations. Journal of Food Engineering, 101(3), 329–336. García-Segovia, P., Pagán-Moreno, M. J., Lara, I. F., & Martínez-Monzó, J. (2017). Effect of microalgae incorporation on physicochemical and textural properties in wheat bread formulation. Food Science and Technology International, 23(5), 437–447. Guerin-Deremaux, L., Li, S., Pochat, M., Wils, D., Mubasher, M., Reifer, C., et al. (2011). Effects of nutriose® dietary fiber supplementation on body weight, body composition, energy intake, and hunger in overweight men. International Journal of Food Sciences & Nutrition, 62(6), 628–635. Han, Q., Yu, Q. Y., Shi, J., Xiong, C. Y., Ling, Z. J., & He, P. M. (2011). Structural characterization and antioxidant activities of 2 water-soluble polysaccharide fractions purified from tea (Camellia sinensis) flower. Journal of Food Science, 76, C462–C470. Ho, L. H., Abdul Aziz, N. A., & Azahari, B. (2013). Physico-chemical characteristics and sensory evaluation of wheat bread partially substituted with banana (Musa acuminata X balbisiana cv. Awak) pseudo-stem flour. Food Chemistry, 139(1–4), 532–539. Jochym, K. K., & Nebesny, E. (2017). Enzyme-resistant dextrins from potato starch for potential application in the beverage industry. Carbohydrate Polymers, 172, 152–158.
3.3.3. Sensory evaluation of the WSRD-substituted bread Sensory evaluation has been widely used as one of the most important methods to evaluate food quality. In terms of total scores, all baked breads obtained higher scores compared with control, and 3% WSRD-treated samples had the highest ones, followed by 5%, 7%, 1% and 10% (w/w) WSRD-treated samples (Table S4). Moreover, all WSRD-treated bread acquired better volume and taste scores than control, and similar results were observed in the appearance and cross section structure except 10% WSRD substitution (Table S4). Therefore, it could be concluded that 3% WSRD-treated breads were the most popular among the participants. Additionally, the testers presented similar preferences for 1%, 5%, and 7% (w/w) WSRD-treated breads. Overall speaking, the results of sensory evaluation are basically consistent with the morphology and texture analysis. Slight discrepancies are acceptable since the high baking temperature and difference of subjective sensation of testers might impact the evaluation results. Moreover, all above facts were also supported by the results of TPA in Table 2. 4. Conclusion The water-soluble WSRD with high purity (83.40%) was fabricated by thermal-acid treatment following amylase hydrolysis using corn starch as raw material. The WSRD possessed a good digestion resistibility, owing to the formation of specific glucosidic bonds of dextrin. The addition of WSRD to flour significantly enhanced the viscoelasticity of dough, which was mainly contributed by the formed gel-like network structures, strengthened gluten aggregation and increased β-sheet conformation. More importantly, WSRD treatment greatly improved 7
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Z. Huang, et al. Jochym, K., Kapusniak, J., Barczynska, R., & Śliżewska, K. (2011). New starch preparations resistant to enzymatic digestion. Journal of the Science of Food and Agriculture, 92(4), 886–891. Kapusniak, J., Kapusniak, K., Ptak, S., Barczynska, R., & Żarski, A. (2014). Products of thermolysis of potato starch treated with hydrochloric and citric acids as potential prebiotics. Quality Assurance and Safety of Crops & Foods, 6(3), 347–356. Laurentin, A., Cárdenas, M., Ruales, J., Pérez, E., & Tovar, J. (2003). Preparation of indigestible pyrodextrins from different starch sources. Journal of Agricultural and Food Chemistry, 51(18), 5510–5515. Linlaud, N. E., Puppo, M. C., & Ferrero, C. (2009). Effect of hydrocolloids on water absorption of wheat flour and farinograph and textural characteristics of dough. Cereal Chemistry, 86(4), 376–382. Lin, S., & Lee, C. (2005). Qualities of chiffon cake prepared with indigestible dextrin and sucralose as replacement for sucrose. Cereal Chemistry, 82(4), 405–413. Liu, G., Wang, J. J., Hou, Y., Huang, Y. B., Wang, J. J., Li, C., et al. (2018). Characterization of wheat endoplasmic reticulum oxidoreductin 1 and its application in chinese steamed bread. Food Chemistry, 256, 31–39. Liu, G., Wang, J. J., Hou, Y., Huang, Y. B., Zhang, Y. P., Li, C., et al. (2017). Recombinant wheat endoplasmic reticulum oxidoreductin 1 improved wheat dough properties and bread quality. Journal of Agricultural and Food Chemistry, 65(10), 2162–2171. Mejia, C. D., Mauer, L. J., & Hamaker, B. R. (2007). Similarities and differences in secondary structure of viscoelastic polymers of maize-zein and wheat gluten proteins. Journal of Cereal Science, 45(3), 353–359. Miyazaki, M., Maeda, T., & Morita, N. (2004). Effect of various dextrin substitutions for wheat flour on dough properties and bread qualities. Food Research International, 37(1), 59–65. Nawrocka, A., Szymańska-Chargot, M., Miś, A., Wilczewska, A. Z., & Markiewicz, K. H. (2017). Aggregation of gluten proteins in model dough after fibre polysaccharide addition. Food Chemistry, 231, 51–60. Ovando-Martinez, M., Sáyago-Ayerdi, S., Agama-Acevedo, E., Goñi, I., & Bello-Pérez, L. A. (2009). Unripe banana flour as an ingredient to increase the undigestible carbohydrates of pasta. Food Chemistry, 113(1), 121–126. Shewry, P. R., Popineau, Y., Lafiandra, D., & Belton, P. (2001). Wheat glutenin subunits and dough elasticity: Findings of the EUROWHEAT project. Trends in Food Science & Technology, 11, 433–441.
Serpelloni, M. (2004). Sugar-free confectionery. U.S. Patent 6,767,576. Serpelloni, M. (2007). Fibre-enriched drinks. U.S. Patent 7,186,433. Sivam, A. S., Sun-Waterhouse, D., Perera, C. O., & Waterhouse, G. I. N. (2013). Application of ft-ir and raman spectroscopy for the study of biopolymers in breads fortified with fibre and polyphenols. Food Research International, 50(2), 574–585. Sudha, M. L., Vetrimani, R., & Leelavathi, K. (2007). Influence of fibre from different cereals on the rheological characteristics of wheat flour dough and on biscuit quality. Food Chemistry, 100(4), 1365–1370. The United States Pharmacopoeia Inc., Rockville, MD, 2000. Wang, L., Liu, H. M., & Qin, G. Y. (2017). Structure characterization and antioxidant activity of polysaccharides from Chinese quince seed meal. Food Chemistry, 234, 314–322. Wang, J. J., Wang, Y. X., Wang, Q. Y., Yang, J. Q., Hu, S. Q., & Chen, L. Y. (2019). Mechanically strong and highly tough prolamin protein hydrogels designed from double-cross-linked assembled networks. ACS Applied Polymer Materials. https://doi. org/10.1021/acsapm.9b00066. Wang, J. J., Liu, G., Huang, Y. B., Zeng, Q. H., Song, G. S., Hou, Y., et al. (2016). Role of N-terminal domain of HMW 1Dx5 in the functional and structural properties of wheat dough. Food Chemistry, 213, 682–690. Wang, J., Rosell, C. M., & Barber, C. B. D. (2002). Effect of the addition of different fibres on wheat dough performance and bread quality. Food Chemistry, 79(2), 221–226. Wang, Q., Li, Y., Sun, F., Li, X., Wang, P., Sun, J., et al. (2015). Tannins improve dough mixing properties through affecting physicochemical and structural properties of wheat gluten proteins. Food Research International, 69(1), 64–71. Wang, Y. J., Kozlowski, R., & Delgado, G. A. (2001). Enzyme resistant dextrins from high amylose corn mutant starches. Starch, 53(1), 21–26. Zhang, Y., Xie, Y., Guo, Y., Cheng, Y., Qian, H., Chen, Y., et al. (2017). The mechanism about the resistant dextrin improving sensorial quality of rice wine and red wine. Journal of Food Processing & Preservation, 41(6), e13281. Zhang, Y., Zhang, H., Wang, L., Qian, H., & Qi, X. (2015). Extraction of oat (avena sativa L.) antifreeze proteins and evaluation of their effects on frozen dough and steamed bread. Food & Bioprocess Technology, 8(10), 2066–2075. Zhou, Y., Zhao, D., Foster, T. J., Liu, Y., Wang, Y., Nirasawa, S., et al. (2014). Konjac glucomannan-induced changes in thiol/disulphide exchange and gluten conformation upon dough mixing. Food Chemistry, 143(2), 163–169.
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Effect of water-soluble dietary fiber resistant dextrin on flour and bread qualities
T
Zheng Huanga,1, Jing Jing Wanga,c,1, Yu Chend, Na Weid, Yi Houb, Weidong Baie, Song-Qing Hua,
⁎
a
Overseas Expertise Introduction Center for Discipline Innovation of Food Nutrition and Human Health (111 Center), School of Food Science and Engineering, South China University of Technology, Guangzhou 510640, China b State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou, Guangdong 510640, China c Department of Food Science and Technology, Foshan University, Foshan 528000, China d Guangdong Food Industry Research Institute Co Ltd, Guangzhou 511400, China e College of Food Science and Technology, Zhongkai University of Agriculture and Engineering, Guangzhou 510225, China
ARTICLE INFO
ABSTRACT
Keywords: Water-soluble resistant dextrin Wheat dough Bread Processing quality Digestion resistibility
A new water-soluble resistant dextrin (WSRD), fabricated by thermal-acid treatment following amylase hydrolysis from corn starch, was expected to strengthen the dietary fibers intake of flour products. This study was to investigate the effects of WSRD on flour processing quality, and further dissect its improvement mechanisms by farinographic and rheological analysis, SDS-PAGE, Fourier transform infrared spectroscopy, texture analyzer, etc. Results showed that WSRD greatly improved the viscoelasticity and strength of dough, which was predominantly contributed by its formation of gel-like networks. Meanwhile, the WSRD-induced increase of gluten aggregates and β-sheet conformation provided the structural basis for enhancing dough quality. Notably, WSRD greatly promoted the sensory appearance and crumb quality of baked breads. Moreover, the WSRD-treated breads resisted the hydrolysis of digestive fluid and enzymes. Therefore, WSRD can strengthen the processing qualities and nutritional values of flour products, which will broaden the application of the novel dietary fiber in flour industry.
1. Introduction Dietary fibers have received particular concern in recent years as they aren’t enzymatically degraded within the human alimentary digestive tract (Brennan & Cleary, 2007). Moreover, the dietary fibers intake is advocated in the nutrition recommendations of several European countries, which promotes the development of grain-rich food as cereal products are the main source of dietary fibers (Wang, Rosell, & Barber, 2002). Therefore, the development of staple foods enriched with fibers is an important contribution to a broader supply of food products with beneficial health effect. As a popular staple food material, wheat flour is used to produce numerous foods such as bread and pasta, and hence it is an ideal candidate to be added with dietary fiber for the nutrient enhancement. Besides the nutritional quality, the dietary fibers inevitably affect the flour processing quality, including the qualities of dough development, texture and baked properties of flour products. Previous studies reported that the addition of dietary fibers usually resulted in a physical
interfering effect and water competition between fibers and gluten (Bock & Damodaran, 2013), which collectively weakened the glutenin network and redistributed the water molecules in the system. Recently, few kinds of dietary fibers are reported to bring positive effects on flour processing quality. Water-soluble resistant dextrin (WSRD) prepared by starch is a new kind of low molecular weight dietary fiber with good solubility (Wang, Kozlowski, & Delgado, 2001), which has been announced as an ordinary food (Zhang et al., 2017). Besides various physiological functions, WSRD has excellent processing performance characterized by its great resistance to acid, alkali and high temperature (Barczynska, Jochym, Slizewska, Kapusniak, & Libudzisz, 2010). WSRD has been widely used in developing low calorie-food (Serpelloni, 2004; Serpelloni, 2007). Lin and Lee (2005) replaced sucrose with commercial resistant dextrin Fibersol-2 to prepare chiffon cakes. Low replacement (< 50%, w/w) of sucrose didn’t significantly affect the sensory characteristics and overall liking of cakes, while high replacement (60%, 80%, w/w) led to the baked cakes with a lower volume, greater
Corresponding author at: Overseas Expertise Introduction Center for Discipline Innovation of Food Nutrition and Human Health (111 Center), School of Food Sciences and Engineering, South China University of Technology, Guangzhou 510641, China. E-mail address: [email protected] (S.-Q. Hu). 1 Z. Huang and J.J. Wang contributed equally to this work. ⁎
https://doi.org/10.1016/j.foodchem.2020.126452 Received 1 August 2019; Received in revised form 18 February 2020; Accepted 18 February 2020 Available online 19 February 2020 0308-8146/ © 2020 Elsevier Ltd. All rights reserved.
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hardness, and lower degree of overall liking. Miyazaki, Maeda, and Morita (2004) found that the low substitution (2.5%, w/w) of conventional dextrin didn’t significantly influence the viscoelasticity of dough, but high substitution (7.5%, w/w) caused poor dough properties and bread quality. Therefore, exploiting new WSRD to enrich and compensate the functions of conventional dextrin is distinctly necessary for low calorie-food industry. In this study, the water-soluble WSRD was fabricated by thermalacid treatment following amylase hydrolysis using corn starch as raw material and food grade paraffin as heat transfer medium. More importantly, the WSRD was added to the flour and expected to not only increase the dietary fiber content of the flour products, but also improve their processing quality. Therefore, the objectives of this study were to qualitatively investigate the effects of different WSRD substitution levels on flour processing quality, and further dissect the related function mechanisms of WSRD. The generated knowledge may offer new opportunities to broaden the application of the novel dietary fiber and provide a kind of healthy and functional ingredient for flour industry.
2.3. Determination of molecular weight distribution of the dextrins The molecular weight distribution of dextrin was determined by gel permeation chromatography in a Waters system comprising a 1525 high-performance liquid chromatography (HPLC) pump with a 717 plus auto sampler and a 2414 refractive index (RI) detector (Waters, America). Dextrin was dissolved in mobile phase (KH2PO4, 0.02 mol/ ml) to obtain the injected concentration of 2 mg/ml. The sample solution was filtered through a membrane filter (0.45 µm). A TSK G5000PWXL column filled with hydrophilic spherical polymethacrylate particles (4 kDa–800 kDa, 7.8 × 300 mm) and a TSK G-3000PWXL column (< 40 kDa, 7.8 × 300 mm) (TOSOH, Japan) was used for the analysis of fractions with a flow rate of 0.6 ml/min. The injected volume was 10 µl and the column temperature was 25 °C. Eight standard dextrins with different molecular weights (2 kDa–800 kDa) were used. The weight-average molecular weight (Mw) was calculated based on the calibration curve. The percentage of particular fractions detected in the chromatograms was calculated using Breeze HPLC Systems (Version 3.3, America) (Wang, Liu, & Qin, 2017; Han et al., 2011).
2. Materials and methods
2.4. In vitro hydrolysis rate of WSRD and bread
2.1. Materials
Anti-digestion of WSRD in simulated gastric fluid (SGF) was determined by the method as follows. The SGF was freshly prepared according to the U.S. Pharmacopoeia (The United States Pharmacopoeia Inc., 2000). Briefly, 3.2 g pepsin and 2.0 g NaCl were dissolved in 1000 ml water and equally divided into three portions, and each pH was adjusted by hydrochloric acid (1.0–3.0). WSRD was dissolved in each SGF with a final concentration of 1% and then digested at 37 ℃ for 5 h. Samples (0.2 ml) from each SGF were collected per 1 h and transferred to tubes containing 0.8 ml distilled water and 1 ml of 3,5 dinitrosalicylic acid (DNS). Tubes were incubated for 10 min at 100 ℃ water bath. Afterwards, 15 ml of distilled water was added to each tube and mixed thoroughly. The released reducing sugar was measured in parallel with the standard curve at 530 nm. In vitro hydrolysis rate of WSRD and bread in simulated intestinal fluid (SIF) were measured according to the method reported by Ovando-Martinez, Sáyago-Ayerdi, Agama-Acevedo, Goñi, and BelloPérez (2009). Briefly, phosphate buffer (pH 7.0) was prepared and equally divided into several portions (50 ml/portion) and each pH (pH 6.0–8.0 for WSRD hydrolysis; pH 7.0 for bread hydrolysis) was adjusted. Pure WSRD or WSRD-treated breads were dissolved in SIF solutions (2%, w/v) and incubated at 37 ℃ for 5 min. Then, 1 ml of αamylase solution (40 mg/ml in DNS solution) was added to each sample to perform the digestion. After 5 h treatment, the hydrolysis rate was determined by DNS method.
Commercial ‘Xinle’ wheat flour (5.35% moisture, 12.50% protein, 0.70% fat and 75.70% carbohydrate, w/w, dry basis) was purchased from Saixin Flour Industry Co., Ltd. (Inner Mongolia, China). All reagents including α-amylase from Bacillus amyloliquefaciens (EC 3.2.1.1, 10–30 U/mg), α-glucosidase from Bacillus stearothermophilus (EC 3.2.1.20, ≥50 U/mg) and pepsin from porcine gastric mucosa (EC 3.4.23.1, ≥250 U/mg) were purchased from Sigma-Aldrich (St. Louis, MO, USA) unless otherwise specified. 2.2. WSRD and its fabrication processing WSRD was fabricated by the method of thermal-acid treatment following amylase hydrolysis from corn starch, which was based on the method reported by Laurentin, Cárdenas, Ruales, Pérez, and Tovar (2003) with some modifications using food grade paraffin as a novel heat transfer medium. 20 g of corn starch was sprayed with 1 ml 0.5% citric acid. After 0.5 h treatment, the samples were dried at 110 ℃ to reach < 5% moisture. Subsequently, the samples were crushed and sieved through a 60 μm mesh screen. Then, the samples were mixed with food-grade paraffin in a 1:1.2 ratio (w/w) and heated at 140 ℃–160 ℃ for 1.5 h to 2 h. After reaction, the mixture was immediately dissolved in distilled water to remove the paraffin to obtain crude dextrin solution. Refining processes including amylase hydrolysis, decolorization, desalting, concentrating and drying were carried out. In detail, the crude solution was adjusted to pH 7.0 and then reacted with 0.5% αamylase at 95 ℃ for 1 h. Afterwards, the temperature was cooled down to 60 ℃ and pH was adjusted to 5.0. The complex enzyme (α-amylase: α-glucosidase = 1:1) was added with a final concentration of 4.0% (w/ v) kept at 60 ℃ for 24 h, i.e. 200–600 U/mL α-amylase and ≥1000 U/ mL α-glucosidase were added into crude solution. Subsequently, the crude solution was heated to 90℃ to terminate the reaction and then filtrated. For decolorization, the filtrate was stirred with 20% activated carbon at 100 ℃ for 20 min. After filtration, the light yellow, clear and tasteless solution was obtained. The desalination treatment was performed using the ion exchange resin, and the final products were concentrated by rotary evaporator. The content of dietary fiber was analyzed according to the enzymatic-gravimetric AOAC official 991.43 method (AOAC, 2003). Meanwhile, the content of protein, fat, ash and moisture were measured according to Kjeldahl (AOAC method 955.04), Soxhlet (AOAC method 960.39) and dry ashing (AOAC method 923.03) and oven drying (AOAC method 977.11), respectively.
2.5. Micro-farinograph analysis and preparation of gluten samples Micro-farinograph measurements and the evaluation of farinogram were performed by AACC-approved methods (AACC, 2000). ‘Xinle’ wheat flour was mixed with different WSRD levels (Table 1) using a 4 g Mixograph (Perten Instrument, Sweden). Effects of WSRD levels (1%, 3%, 5%, 7%, 10%, w/w, flour base) on dough quality were investigated. Farinography parameters including water absorption (WA), dough development time (DDT), dough stability time (DST) and degree of softening index (DSI) were recorded. Five replicates were tested for each group. Dough and gluten samples were prepared based on Wang et al. (2016) and then wrapped with plastic wrap to prevent the loss of water, and then divided into three parts: the first part was used for rheological measurement; the second part was lyophilized to obtain freeze-dried dough; the third part was employed to obtain the freeze-dried gluten. The gluten was ground into powder and sieved through a 180 μm mesh screen, then stored at –20 °C for SDS-PAGE analysis. 2
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Table 1 Effect of resistant dextrin on farinogram parameters. WSRD level (%, w/w) Control 1 3 5 7 10
WA (%, w/w) 61.45 60.65 56.84 52.00 51.20 45.20
± ± ± ± ± ±
DDT (min) e
0.07 1.20d 0.42c 0.00b 1.56b 0.00a
2.60 2.03 3.47 4.20 4.90 4.25
± ± ± ± ± ±
DST (min) a
0.14 0.93a 0.42b 0.40b 0.14b 0.21c
DSI (FU) a
3.40 ± 0.28 3.63 ± 0.06a 4.88 ± 0.19b 6.33 ± 0.31c 7.60 ± 0.00d 17.15 ± 0.07e
144.90 ± 0.00c 153.23 ± 11.55d 133.27 ± 7.58c 105.00 ± 13.23b 87.50 ± 3.54b 45.00 ± 5.00a
Different letters in the same column indicate a significant difference (p < 0.05, n = 5).
2.6. Dynamic rheological determination.
2.11. Texture analysis and sensory evaluation of WSRD-treated bread
Rheological characterization of dough was based on Wang et al. (2016). The rheological behavior of dough was analyzed by a rheometer (AR1500ex, TA, USA). The linear viscoelastic region was determined by a frequency sweep test from 0.1 to 10 Hz with 0.1% deformation. Rheological parameters including storage modulus (G'), loss modulus (G''), complex modulus G* = G'2+G''2 and loss tangent (tan δ) were recorded.
The bread volume was determined by seed displacement method (Wang et al., 2002). Crumb texture was determined by a texture analyzer (TA-XT Plus, UK) equipped with a 25 mm diameter probe. Bread slices of 2 cm thickness were compressed to 40% of their original height. Three replicates were tested for each group. The sensory evaluation of fresh breads was performed according to the studies of Burešová, Masaříková, Hřivna, Kulhanová, and Bureš (2016) and Ho, Abdul Aziz, and Azahari (2013). In detail, 10 trained panelists from the major of food science and technology in South China University of Technology were invited. The sensory evaluation was carried out as follows: 6 groups of bread samples were prepared and randomly coded with the number from 1 to 6, respectively. And then, the panelists were asked to evaluate the sensory parameters of the bread samples, including volume, color, appearance, texture and taste according to the evaluation standard in Table S1. Before analyzing the results, the maximum and minimum scores for each group were removed and the remaining 8 scores were averaged as the final score.
2.7. Protein electrophoresis Protein solutions (20 μl, 20 mg/ml) were mixed with 5 μl loading buffer (62.5 mM Tris-HCl, 20% glycerol (v/v), 1% SDS (w/v), pH 6.8) for non-reducing SDS-PAGE. The discontinuous system consisted of separating gel (12%, pH 8.6) and stacking gel (5%, pH 6.8). The gel was stained with Coomassie Brilliant Blue (0.25% R-250, 45% methanol and 10% acetic acid) and de-stained in methanol and acetic acid solution (methanol/acetic acid/water = 1:1:8, v/v/v). The molecular weight of protein standard markers ranges from 14.4 kDa to 116 kDa.
2.12. Statistical analysis Values were shown in the means ± standard deviation of three replicate samples unless otherwise specified. One-way analysis of variance (ANOVA) was used to compare the value differences under different treatments (p < 0.05) by SPSS software (Version 17.0, SPSS Inc., USA).
2.8. Scanning electron microscopy (SEM) The microstructure of dough was observed by SEM (Evo 18, Carl Zeiss, Germany). The freeze-dried dough samples were fixed to the sample holder and sputter-coated with gold. Subsequently, the samples were transferred to the microscope and observed at 10.0 kV with a vacuum of 9 × 10−5 MPa.
3. Results and discussion 3.1. WSRD improved the digestion resistibility of bread 3.1.1. Digestion resistibility of WSRD in SGF and SIF The weight-average molecular weight (Mw) of the products from the treated corn starch was 3.89 kDa (Fig. S1) which was generally similar to the Mw of potato starch-based dextrin reported by Jochym, Kapusniak, Barczynska, and Śliżewska (2011) and Kapusniak, Kapusniak, Ptak, Barczynska, and Żarski (2014). Meanwhile, the generation of α-1,3-glucosidic bond, a typical covalent bond indicator of dextrin, was determined (Fig. S2) during the dextrinization of corn starch. The composition analysis showed that the products contained high dietary fiber reaching 83.40 ± 1.16%, 0.50 ± 0.03% protein, 0.34 ± 0.02% fat, 0.05 ± 0.01% ash and 4.40 ± 0.78% moisture. Furthermore, the product presented good water-solubility for its watersolution at 1% (w/v) or 10% (w/v) concentration was transparent and no precipitation appeared (Fig. S3). Therefore, all these results indicated that the raw corn starch was completely degraded to watersoluble resistant dextrin (WSRD). The prominent feature of WSRD is resisting the hydrolysis of human digestive fluid and enzymes (Guerin-Deremaux et al., 2011). In Fig. 1A, the hydrolysis degree of WSRD in SGF increased with the pH decreasing from 3.0 to 1.0 under the same treatment time. At each given pH, the hydrolysis degree of WSRD slightly increased with the treatment time increasing, and almost reached the plateau after 4 h. However, the
2.9. Fourier transform infrared spectroscopy (FT-IR) The FT-IR spectra were determined by a Bruker Vertex-70 spectrometer (Bruker Optics, Ettlingen, Germany). The gluten samples were mixed with KBr and then a total of 64 scans from 400 to 4000 cm−1 against the background were taken at 4 cm−1 resolution. The curvefitting and peak area corresponding to the different secondary structures were obtained using PeakFit version 4.12 software (Wang et al., 2016). 2.10. Breadmaking procedure The breadmaking procedure was performed according to Liu et al. (2017). The bread formula was consisted of 100 g WSRD substituted wheat flour, 3 g vegetable oil, 3 g pure milk, 3 g NaCl, 5 g sucrose, 1 g dry yeast (Angle Brand, China) and the corresponding water determined by farinograph. All raw materials were mixed using an automatic machine and the dough was divided into three pieces (45 g/ piece). After proofing at 35 °C for 90 min, the dough was baked at 190 °C for 10 min. Loaves were taken out and cooled down for 1 h before texture analysis. 3
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Fig. 1. Hydrolysis degree of WSRD in simulated gastric fluid (A), simulated intestinal fluid (B) and WSRD-treated bread in simulated gastric fluid (C).
significantly influenced by WSRD (Table 1). With WSRD levels ranging from 1% to 10%, the WA was significantly (p < 0.05) decreased from 60.65% to 45.20%, which was obviously lower than control (61.45%). The decreased WA was probably due to that the added WSRD diluted the glutenin and hence weakened the formation of gluten networks (Miyazaki et al., 2004; Wang et al., 2016), because glutenin especially its formed networks played an important role in absorbing and retaining water (Wang et al., 2016; Chen et al., 2019). Such facts were supported by Zhou et al. (2014), reporting that the diluted glutenin impeded the massive formation and the swelling of gluten network. For DDT, WSRD substitution greatly (p < 0.05) elevated its values from 2.03 min to 4.90 min, indicating that WSRD delayed the formation of gluten matrix. DST reflecting the resistance of the dough against the blades is another key indicator for flour processing quality. Compared with control (3.40 min) (Table 1), the DST of WSRD-treated dough was markedly increased from 3.63 min at 1% level to 17.15 min at 10% level, indicating that WSRD improved the flour processing quality. The massive formation of strengthened gluten networks is responsible for the improvement of farinogram parameters (Wang et al., 2016). In this study, the WSRD substitution should weaken and delay the formation of gluten networks from WA and DDT results. However, the DST results implied that the WSRD-treated dough exhibited an excellent resistance against the shear stress. Therefore, it was inferred that an unknown structures or components inside the dough enhanced the processing quality of flour.
highest hydrolysis degree didn’t exceed 1.5%, indicating that WSRD was difficult to be hydrolyzed in SGF. Compared to SGF, SIF-treated changes in hydrolysis degree of WSRD presented opposite trends with the alteration of pH (Fig. 1B). Under the same time, the hydrolysis degree of WSRD in SIF increased with the pH increasing from 6.0 to 8.0. With the increase of time, all hydrolysis degrees exhibited a slight increase but didn’t exceed 4.0% at each pH, also suggesting that WSRD was difficult to be hydrolyzed in SIF. The digestion resistibility of WSRD to SGF and SIF was greatly attributed to the generation of α-1,2- and α-1,3-glucosidic bonds at the expense of α-1,4- and α-1,6-glycosidic bonds during dextrinization of corn starch. It is well known that the human digestive enzymes (mainly α-amylase) mostly take α-1,4- and α-1,6-glycosidic bonds as hydrolysis targets, while the formation of new α-1,2- and α-1,3-glucosidic bonds (Fig. S2) makes dextrin less susceptible to the digestive enzymes (Jochym & Nebesny, 2017). 3.1.2. Digestion resistibility of WSRD-treated bread In Fig. 1C, the hydrolysis degree of bread without WSRD was 92.1%. As WSRD levels increased from 1% to 10%, the hydrolysis of bread significantly (p < 0.05) decreased from 91.8% to 84.5%. Therefore, WSRD improved the digestion resistibility of bread, especially when the WSRD levels reached 7% and 10%. During WSRD preparation, those easily digested glycoside bonds have been cleaved and destroyed by enzymes and acid-heat treatment. Meanwhile, some branched structures which were difficult to be hydrolyzed newly formed. Therefore, WSRD could resist the hydrolysis of most human digestive enzymes, resulting in a mild glycemic response. Consequently, WSRD will be the potential ingredients of special foods for people with diabetes. Meanwhile, WSRD is also expected to help people with over-weight and cardiovascular disease (Guerin-Deremaux et al., 2011).
3.2.2. Effects of WSRD on the rheological properties of dough The rheological properties of WSRD-treated dough are shown in Fig. 2. In Fig. 2A and B, the G' and G'' of all samples increased with the frequency increasing, and the G' was higher than G''. Meanwhile, all tan δ values were less than 1 (Fig. 2D), meaning that the G' of all samples were more prominent. According to Demirkesen, Mert, Sumnu, and Sahin (2010), such phenomenon indicated that the WSRD-treated dough had a weak gel behavior or solid like structure. In detail, when the frequency was lower than 5 Hz, the WSRDtreated dough presented an overall decrease in G' with its substitution levels increasing from 1% to 10%, suggesting that the gel networks
3.2. WSRD improved flour processing quality 3.2.1. Effects of WSRD on the farinographic properties of dough Compared with control, the WA, DDT, DST and DSI of dough were 4
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Fig. 2. Effects of WSRD on the rheological properties of dough. (A) elastic moduli (G′); (B) viscous moduli (G″); (C) complex moduli (G*); (D) loss tangent (tan δ).
Fig. 3. Effects of WSRD on microstructures of dough. (A) Control dough; (B) 1% WSRD-treated dough; (C) 3% WSRD-treated dough; (D) 5% WSRD-treated dough; (E), (G) 7% WSRD-treated dough; (F), (H) 10% WSRD-treated dough.
Fig. 4. Photos of bread (A) and slices (B) made from the WSRD-treated dough.
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Table 2 Effects of WSRD on the qualities of bread prepared by medium-gluten flour. WSRD (%, w/w) Control 1 3 5 7 10
SV (×10−3 m3/kg) 6.69 6.59 7.71 7.61 8.07 6.54
± ± ± ± ± ±
a
0.14 0.26a 0.07b 0.14b 0.03c 0.40a
Hardness (×10−3 kg) 1775.12 1520.45 2290.85 2016.80 1535.12 1456.04
± ± ± ± ± ±
Chewiness (×10−3 kg)
b
46.77 22.29a 78.44d 140.68c 54.10a 0.00a
1540.10 1284.42 1873.97 1610.07 1272.28 1120.76
± ± ± ± ± ±
c
32.86 12.05b 40.83d 121.88c 12.81b 0.00a
Springiness 0.87 1.00 1.00 1.00 1.00 1.00
± ± ± ± ± ±
Cohesiveness a
0.04 0.01a 0.00a 0.00a 0.01a 0.00a
0.87 0.85 0.82 0.80 0.83 0.77
± ± ± ± ± ±
0.04b 0.01b 0.01a 0.00a 0.04b 0.00a
SV: specific loaf volume; Letters within a column indicate significantly different values (p < 0.05, n = 3).
proteins (HMMP, > 97 kDa) were extracted from WSRD-treated dough. As the amount of WSRD increased, the band intensity (red box) of HMMP gradually increased, suggesting that WSRD improved the HMMP formation. The amounts of glutenin polymers, particularly high molecular weight polymers, were positively correlated with dough strength (Wang et al., 2016). Therefore, the results supported that WSRD enhanced the dough strength from rheological results (Fig. 2C). Changes in secondary structures of gluten are related to the dough development (Mejia, Mauer, & Hamaker, 2007). In Table S3, the βsheet structure was the dominant component in all WSRD-treated gluten, which was consistent with the report of Wang et al. (2015). Compared with the control, the proportion of β-sheet structure gradually increased from 50.3% to 54.6% as the WSRD increased from 1% to 10%. During the dough development, the increase in β-sheet was an indicator of high molecular aggregates formation (Wang et al., 2016), which was reflected by SDS-PAGE analysis (Fig. S4). More importantly, such results confirmed the functional characteristics of WSRD from a structural level. However, the proportion of β-turn structure decreased from 26.3% to 21.8%, and the significant changes in α-helix and random coils weren’t observed. In conclusion, the addition of WSRD favored the transition of β-turn to β-sheet. Such behavior can be reasonably explained by the widely accepted “Loop and Train” model of dough. The model proposes that the “train” region is associated with β-sheets while the “loop” with extended hydrated β-turns. The dough system gets plasticized allowing β-turns in adjacent β-spirals to form interchain β-sheets with the water content increasing. Further hydration breaks some interchain H bonds between glutamine residues leading to the formation of loops consisting of βturns (Shewry, Popineau, Lafiandra, & Belton, 2001). In control, the dough got sufficient water, so the gluten proteins formed the “loop” where protein–water–protein interactions formed. When WSRD was added, the mobility of the hydrated segments would be reduced, owing to the water competition between protein and WSRD. Consequently, WSRD increased the intermolecular contacts and binding sites for H bonding to form extended β-sheet in dough. Similar results have been reported by Sivam, Sun-Waterhouse, Perera, and Waterhouse (2013), showing that pectin and polyphenols-treated breads gained more βsheet conformation at the expense of β-turn. Another study of Nawrocka, Szymańska-Chargot, Miś, Wilczewska, and Markiewicz (2017) also reported that the cooperation of inulin with gluten formed more β-sheet at the expense of β-turn.
were elastic but weak. However, the WSRD-treated dough possessed an increased G' during 5 Hz to 10 Hz, implying the gel networks became stronger (Wang et al., 2019). Interestingly, 3% WSRD-treated dough presented different changes in rheological parameters, which needs future investigation. Additionally, G* was employed to characterize the stiffness of dough. Changes in G* showed a similar trend with G′ (Fig. 2C), implying that WSRD strengthened the stiffness of dough. Bread quality is directly related to the gluten structures which form continuous and viscoelastic networks in dough. Previous studies revealed that the viscoelasticity of dough was associated with glutenin, because glutenin macropolymers (GMP) were the main components that held the gluten networks together (Anjum et al., 2007). In theory, the WSRD substitution inevitably reduced the GMP content owing to the dilution of glutenin, which should negatively affect the rheological properties of dough. However, WSRD finally improved the formation of gluten networks and enhanced the stiffness of dough (Fig. 2). Therefore, these results further supported that there was an unknown structures or components from WSRD substitution compensating the negative impacts of diluted glutenin. 3.2.3. Effects of WSRD substitution on the microstructure of dough The microstructures of wheat doughs with or without WSRD clearly displayed the gluten matrix (G), large starch granules (LS), small starch granules (SS) and the formed gel-like network structures (GNS) on the gluten matrix (Fig. 3). In Fig. 3A, control samples showed the typical microstructure of dough in which starch granules were wrapped in gluten proteins to support the gluten matrix (Correa, Anon, Perez, & Ferrero, 2010). In 1% and 3% WSRD-treated dough (Fig. 3B and C), some filamentous and thin lamellar gel-like structures were observed. When WSRD reached 5% and 7%, the gel network structures became much obvious (Fig. 3D and E). Further elevating WSRD to 10% (Fig. 3F), the network structures became relatively continuous, suggesting the formation of a new network. At higher (1500×) magnifications, similar structures could still be found, and the cross-linked structures were more visible (Fig. 3G and H). Considering above analysis, the unknown structure or component was none other than this gel network structure formed by WSRD enhancing the processing quality of flour. Various water-soluble dietary fibers are capable of forming gels, and their aqueous solutions usually possess viscosity or adhesiveness. To verify this point, the viscosity and adhesiveness of 50% WSRD aqueous solution (w/v) were determined (Table S2). Results showed that the values of viscosity and adhesiveness of WSRD solutions could be highly comparable to the commercial liquid glue (Deli Brand, No.7303, China). Additionally, similar gel-like network structures have been mentioned in other studies (Sudha, Vetrimani, & Leelavathi, 2007; Ho et al., 2013). For example, Linlaud, Puppo, and Ferrero (2009) found that more elastic networks formed in dough in the presence of xanthan and guar gum. Therefore, the gel network structures were firmly believed to be constructed by the WSRD after hydration, which in turn enhanced the farinographic (Table 1) and rheological properties of dough (Fig. 2).
3.3. WSRD-substitution improved the quality of baked bread 3.3.1. Morphology of WSRD-treated bread Overall speaking, the surface of WSRD-treated bread gradually became smoother as the WSRD level increased (Fig. 4A). An obvious crevice structure appeared on the surface of control and 1% WSRDtreated breads. The crevices were gradually seamed with the WSRD levels ranging from 3% to 7%, and even disappeared at 10% WSRD level. Volume analysis showed that the control, 1% or 10% WSRD-treated breads almost had the same volume (Table 2). When 3%–7% WSRD was added, the bread volume significantly increased, and reached the
3.2.4. Effects of WSRD on the gluten aggregates and structures SDS-PAGE was carried out to understand the effects of WSRD on the gluten aggregates formation (Fig. S4). SDS-soluble high molecular mass 6
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maximum 8.07× 10−3 m3/kg at 7% WSRD substitution. Changes in the bread volume were consistent with the pore distribution in crumb, because there were sporadic and unevenly distributed pores in the control, 1% and 10% WSRD-treated breads, while even and dense pores were spread in 3%, 5% or 7% WSRD-treated samples (Fig. 4B). It has been clarified that the gluten networks have high availability to retain the carbon dioxide produced by yeast during proofing and baking, which determines the loaf volume and crumb structure (Liu et al., 2018). Meanwhile, a good paste must retain sufficient viscosity to prevent the incorporated air bubbles being lost during heating (Zhang, Zhang, Wang, Qian, & Qi, 2015). In this study, the WSRD formed the gel network structures (Fig. 3) and enhanced the viscoelasticity and stiffness of dough (Fig. 2), which greatly contributed to the bread quality. However, the excessive addition of WSRD led to the deterioration of bread volume, mainly due to that an overly strong gel network limited the expansion of dough during fermentation and baking (Liu et al., 2018).
the sensory appearance and crumb quality of baked breads. Moreover, WSRD-treated breads could resist the hydrolysis of digestive fluid and human digestive enzymes as expected. Therefore, the WSRD has the potential to be a healthy and functional ingredient used in wheat flour products for enhancing their processing qualities and nutritional values. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This research was supported by the National Natural Science Foundation of China (grant numbers 31771906), Science and Technology Planning Project of Guangzhou City, China (grant number 201604020032), Science and Technology Planning Project of Shaoguan City, China (grant number Shaoke-2017-62), and the 111 project (grant number B17018). Jing Jing Wang is grateful to the financial support from Shanghai Ocean University Funding (A2-2006-00-200364 and A22006-00-574200221).
3.3.2. Effects of WSRD on the bread texture Texture of WSRD-treated breads crumb was further analyzed by TPA. Compared with control, the hardness of 1%, 7% and 10% WSRDtreated breads significantly decreased, while 3% and 5% WSRD-treated samples obviously increased, and the maximum hardness reached 2290.85 g at 3% WSRD levels (Table 2). Crumb chewiness reflects the energy required to masticate food to a state ready for swallowing (García-Segovia, Pagán-Moreno, Lara, & Martínez-Monzó, 2017). The chewiness parameters presented a similar change with the hardness values, that’s to say, relatively lower WSRD substitution (3%, 5%) markedly improved the bread chewiness, while higher WSRD (7%, 10%) obviously decreased the chewiness. Based on the study of Bourne and Malcolm (2003), the bread with appropriate WSRD level tended to remain in the mouth without rapidly breaking up or dissolving. Significant changes in springiness and cohesiveness were not observed for all WSRD-treated samples. All results implied that the WSRD did possess the ability to strengthen the processing quality of medium-gluten flour.
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.foodchem.2020.126452. References AACC (2000). Approved methods of the American association of cereal chemists. St. Paul MN: The Association. Anjum, F. M., Khan, M. R., Din, A., Saeed, M., Pasha, I., & Arshad, M. U. (2007). Wheat gluten: high molecular weight glutenin subunits–structure, genetics, and relation to dough elasticity. Journal of Food Science, 72(3), R56–R63. AOAC (2003). Total, soluble and insoluble dietary fibre in foods and food products, enzymatic-gravimetric method. In Horwitz, W. (ed.) Official methods of analysis of AOAC International. Barczynska, R., Jochym, K., Slizewska, K., Kapusniak, J., & Libudzisz, Z. (2010). The effect of citric acid-modified enzyme-resistant dextrin on growth and metabolism of selected strains of probiotic and other intestinal bacteria. Journal of Functional Foods, 2(2), 126–133. Bock, J. E., & Damodaran, S. (2013). Bran-induced changes in water structure and gluten conformation in model gluten dough studied by fourier transform infrared spectroscopy. Food Hydrocolloids, 31(2), 146–155. Bourne, M. C., & Malcolm, C. (2003). Food texture and viscosity: concept and measurement. International Journal of Food Science & Technology, 38(7), 839–840. Brennan, C. S., & Cleary, L. J. (2007). Utilisation glucagel in the β-glucan enrichment of breads: A physicochemical and nutritional evaluation. Food Research International, 40(2), 291–296. Burešová, I., Masaříková, L., Hřivna, L., Kulhanová, S., & Bureš, D. (2016). The comparison of the effect of sodium caseinate, calcium caseinate, carboxymethyl cellulose and xanthan gum on rice-buckwheat dough rheological characteristics and textural and sensory quality of bread. LWT – Food Science and Technology, 68, 659–666. Chen, M., Wang, L., Qian, H. F., Zhang, H., Li, Y., Wu, G. C., et al. (2019). The effects of phosphate salts on the pasting, mixing and noodle-making performance of wheat flour. Food Chemistry, 283, 353–358. Correa, M. J., Anon, M. C., Perez, G. T., & Ferrero, C. (2010). Effect of modified celluloses on dough rheology and microstructure. Food Research International, 43(3), 780–787. Demirkesen, I., Mert, B., Sumnu, G., & Sahin, S. (2010). Utilization of chestnut flour in gluten-free bread formulations. Journal of Food Engineering, 101(3), 329–336. García-Segovia, P., Pagán-Moreno, M. J., Lara, I. F., & Martínez-Monzó, J. (2017). Effect of microalgae incorporation on physicochemical and textural properties in wheat bread formulation. Food Science and Technology International, 23(5), 437–447. Guerin-Deremaux, L., Li, S., Pochat, M., Wils, D., Mubasher, M., Reifer, C., et al. (2011). Effects of nutriose® dietary fiber supplementation on body weight, body composition, energy intake, and hunger in overweight men. International Journal of Food Sciences & Nutrition, 62(6), 628–635. Han, Q., Yu, Q. Y., Shi, J., Xiong, C. Y., Ling, Z. J., & He, P. M. (2011). Structural characterization and antioxidant activities of 2 water-soluble polysaccharide fractions purified from tea (Camellia sinensis) flower. Journal of Food Science, 76, C462–C470. Ho, L. H., Abdul Aziz, N. A., & Azahari, B. (2013). Physico-chemical characteristics and sensory evaluation of wheat bread partially substituted with banana (Musa acuminata X balbisiana cv. Awak) pseudo-stem flour. Food Chemistry, 139(1–4), 532–539. Jochym, K. K., & Nebesny, E. (2017). Enzyme-resistant dextrins from potato starch for potential application in the beverage industry. Carbohydrate Polymers, 172, 152–158.
3.3.3. Sensory evaluation of the WSRD-substituted bread Sensory evaluation has been widely used as one of the most important methods to evaluate food quality. In terms of total scores, all baked breads obtained higher scores compared with control, and 3% WSRD-treated samples had the highest ones, followed by 5%, 7%, 1% and 10% (w/w) WSRD-treated samples (Table S4). Moreover, all WSRD-treated bread acquired better volume and taste scores than control, and similar results were observed in the appearance and cross section structure except 10% WSRD substitution (Table S4). Therefore, it could be concluded that 3% WSRD-treated breads were the most popular among the participants. Additionally, the testers presented similar preferences for 1%, 5%, and 7% (w/w) WSRD-treated breads. Overall speaking, the results of sensory evaluation are basically consistent with the morphology and texture analysis. Slight discrepancies are acceptable since the high baking temperature and difference of subjective sensation of testers might impact the evaluation results. Moreover, all above facts were also supported by the results of TPA in Table 2. 4. Conclusion The water-soluble WSRD with high purity (83.40%) was fabricated by thermal-acid treatment following amylase hydrolysis using corn starch as raw material. The WSRD possessed a good digestion resistibility, owing to the formation of specific glucosidic bonds of dextrin. The addition of WSRD to flour significantly enhanced the viscoelasticity of dough, which was mainly contributed by the formed gel-like network structures, strengthened gluten aggregation and increased β-sheet conformation. More importantly, WSRD treatment greatly improved 7
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