Effect of glutathione on gelatinization and retrogradation of wheat flour and starch

Reduced glutathione (GSH) commonly exists in wheat flour and has remarkable influence on gluten properties. In this study, effect of GSH on the gelatinization and retrogradation of wheat flour and wheat starch were investigated to better understand the GSH-gluten-starch interactions in wheat flour. Compared with wheat starch, wheat flour showed significant decreases in peak and final viscosity, and gelatinization onset temperature with increasing GSH concentration. GSH depolymerized gluten and thereby broke down the protein barrier around starch granules to make the starch easily gelatinized. However, the interaction between GSH and wheat starch restrained starch swelling. GSH addition resulted in weakened structure with higher water mobility in freshly gelatinized wheat flour dispersions but decreased water mobility in wheat starch dispersions. After storage at 4 °C for 7 d, GSH increased elasticity and retrogradation degree in wheat flour dispersions but retarded retrogradation in wheat starch dispersions. The results indicated that GSH promoted retrogradation of wheat flour, which mainly attributed to the depolymerized gluten embedding in the leached starch chains, and inhibiting the re-association of amylose, and subsequently promoted the starch intermolecular associations and starch retrogradation. This study could provide valuable information for the control of the quality of wheat flour-based products.     

Investigation on morphological structure and crystal transition of maize starch gelatinized in pure glycerol

The gelatinization phenomena and crystalline structure of maize starch gelatinized in pure glycerol were investigated using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Starch granules were firstly treated in water system, CLSM and SEM micrographs displayed that they were completely broken and the characteristic birefringence of the starch granules disappeared at 70 °C. As for pure glycerol system, the starch granules swelled but maintained granular shape with the increasing of temperature. The crystalline structure of starch granules was partially destroyed at 130 °C and completely destroyed at 140 °C. The DSC thermogram showed that the gelatinization temperature of starch in glycerol started at 123.7 °C, peaked at 128.4 °C, and concluded at 135.2 °C. The X-ray diffractograms indicated that the crystalline structure of maize starch was partially destroyed at 130 °C and completely destroyed at 140 °C. Thus, glycerol served an alternative solvent to destroy crystalline structure of maize starch, which may be helpful for hydrolysis of starch granules by amylase in food industry.     

Effects of wheat bran with different colors on the qualities of dry noodles

White, blue, black and purple red wheat bran powders were prepared by ultrafine grinding to the particle size distribution of 0.5–100 μm. The effects of wheat bran addition on the qualities of dry Chinese noodles were investigated. Rapid Visco Analyzer results suggested that peak viscosity, hot paste viscosity, cool paste viscosity, breakdown viscosity and setback viscosity of the blends decreased with the increasing bran levels from 2.0% to 6.0% (P < 0.05). Color of dough sheet (L*) decreased with the addition of wheat bran, while a* and b* values increased distinctly. Water absorption and firmness of the cooked noodles showed up trends with increasing addition of bran, while cooking loss showed a downtrend. Tensile strength and elongation rate decreased when bran addition was 2.0%, but increased when bran addition reached 4.0%–6.0%. Storage modulus (E′) and loss modulus (E″) showed decreasing trends with increases in bran addition at frequencies of 0.1–10 Hz. SEM revealed that bran presence could slightly decrease surface connectivity between starch granules and gluten. It is possible to produce fiber-rich noodles by using 2.0%–6.0% ultrafine-ground bran in wheat flour.     

Physicochemical characterization and in-vitro digestibility of extruded rice noodles with different amylose contents based on rheological approaches

The physicochemical properties and in-vitro digestibility of extruded rice noodles with different amylose contents were characterized from a rheological point of view. Thermo-mechanical measurements showed that the rice flour with higher amylose contents exhibited greater stability to dual-mixing and higher degrees of starch gelatinization and retrogradation. In addition, greater elastic properties were clearly observed in the high amylose rice samples. The use of high amylose rice flour produced noodles with a harder texture, consequently contributing to reduced cooking loss. Furthermore, the rheological changes of extruded rice noodles were monitored in real time during the in-vitro starch digestion. The rice noodle digesta with higher amylose contents exhibited greater viscosities throughout the simulated oral-gastric-intestinal digestion steps. The flow behaviors of the rice noodle digesta consisted of the Power-law region and infinite shear plateau that were satisfactorily characterized by the Sisko model (R² > 0.99).     

Scanning Electron Microscopic Study of Dough and Chapati from Gluten-reconstituted Good and Poor Quality Flour

Hard and soft wheat flours, which were used in the study, resulted in good and poor quality chapatis respectively. Gluten was isolated and interchanged among the two whole wheat flours and studied by scanning electron microscopy for its influence on structural characteristics of dough and its relation to chapati-making quality. Microscopic observations clearly indicated that larger gluten strands covered starch granules in hard wheat flour dough, while gluten was short and starch granules exposed in dough prepared from soft wheat flour. Greater film forming ability of gluten in hard wheat flour dough manifested in long and bulky starch strands interwoven with protein matrix in its chapati crumb. Higher moisture retention and starch gelatinization as a consequence of greater film forming ability of gluten in hard wheat flour resulted in pliable and soft textured chapati.     

Effect of heating temperature on the particle size distribution in waxy wheat flour

The particle size of waxy (amylose-reduced) wheat (Triticum aestivum L.) starch was determined at isothermal temperatures by laser diffraction analysis. Flour samples were suspended in deionized water at temperatures ranging from 30 to 90 °C for 20–60 min. At 30 °C, all of the flour particles exhibited trimodal size distributions, i.e., the particles in the first, second, and third modes were <10 μm, 10–50 μm, and 51–300 μm, respectively. Control experiments with isolated starch indicated that the first and second modes were associated mainly with starch granules, whereas the third mode may have been related to gluten and gluten adhesion. The particle size distributions of waxy segregant wheat flours were temperature dependent. At 60 °C, there were significant changes in the particle size and distribution of waxy flours, which indicated the swelling of starch granules in response to elevated temperature. As the temperature increased, the peak particle size of waxy segregant wheat flours increased in different ways. The results suggest that variations in the swelling properties of selected waxy genotype flours may be due to the strength of starch–protein interaction and the capacity for starch granule gelatinization.     

Milling,functional and thermo-mechanical properties of wheat,rye, triticale,barley and oat

The milling potential of hulled barley, hulled oat, triticale, rye and wheat was studied using a long tempering process and a laboratory four-roller mill. Regardless of the investigated cereal, the results indicated a significant influence (p < 0.05) of volume per surface area ratio on the milling yield and ash contents of the flour. The lowest milling yield was obtained in case of hulled oat. Solvent retention capacity profiles were determined for all investigated whole cereals and flours for predicting the contribution of different polymers to the functionality of samples. For all solvents higher values were obtained for the whole cereals compared to the corresponding flour. Thermo-mechanical properties of the whole cereals and refined flours were also investigated. If in case of wheat the gluten proteins play an essential role on dough behaviour during kneading at 30 °C, in case of triticale, rye, hulled barley and hulled oat, the fibers play a major role as well. Thermo-mechanical properties of starch registered a large variation between cereals and/or flours. The lowest torque value corresponding to starch gelatinization (C3) was registered in case of the hulled oat flour, 1.92 Nm, while the highest value in case of rye flour, 2.65 Nm.     

Simulating the formation of bread crust in a DMTA rheometer

Water evaporates very fast from the surface layers of dough, enhanced by high heating rates at the beginning of baking. The rheological properties of the surface layers play an important role during the baking process, especially in local and overall expansion and water loss. The aim of this study was to determine the rheological properties of bread dough in the heat-moisture dynamics of the baking process, especially in surface drying and delayed drying conditions. The DMTA method was used in tensile mode in order to expose the samples to fast dehydration to simulate real bread crust. The degree of starch gelatinization was demonstrated by the disappearance of the “Maltese cross” (polarized light microscopy). Temperature and water content were monitored during baking. The modulus evolution depended on both the heat and moisture evolution (i.e. immediate or delayed in the present study). In contrast to reports in the literature, starch gelatinization was observed even under drying conditions. Nevertheless, comparison between samples under drying and under delayed drying conditions suggested that water content prevailed in the rheological changes.     

Improvement of noodle quality: The effect of ultrasonic on noodles resting

In order to overcome the existing challenges on the production time and quality, a novel dough resting method of fresh wet noodles via ultrasonic processing was developed. The changes of the starch, protein hydration and gluten network formation after ultrasonic treatment were investigated. The sensory quality, secondary structure and cross section morphology of dough were characterized. The results showed that ultrasonic treatment could improve the texture of wheat dough, promote the hydration of starch and protein, and increase the cooking quality. Compared with the control group, the hardness of fresh noodles decreased by 14.19%, and tensile force significantly increased by 33.43% after treatment under ultrasonic power density of 66 W/L. Viscoelastic, SEM and FTIR characterization results also verified that the angle of loss (tanδ) and surface roughness was decreased, and the content of α-helix significantly increased via ultrasonic treatment. It could be observed that the ultrasonic resting could reduce the surface tension between protein and water molecules to promote the formation of gluten network and protein hydration. Therefore, ultrasonic treatment could facilitate to reduce the resting processing time and improve the quality of fresh wet noodles.     

Modification of physicochemical properties and in vitro digestibility of wheat flour through superheated steam processing

Native and moistened wheat flours (moisture contents were 13.5 and 27.0%, respectively) were treated with superheated steam (SS) at different temperatures (140 and 170 °C) and times (1, 2 and 4 min). Their physicochemical and digestive properties were analyzed. For native flour, SS treatment altered the starch molecular structure and behavior slightly. While for moistened flour, crystalline degree, gelatinization enthalpy, amylose leaching (AML) and falling number significantly decreased, but thermal transition temperatures increased with the rise of treating severity. Clumping of starch granules, aggregation of proteins and formation of amylose-lipid complexes occurred in both native and moistened flours. Broader pasting temperature ranges and higher viscosities were found on SS-modified flours. Additionally, SS treatment on moistened flours increased resistant and slowly digestible starch contents. In general, SS treatment induced changes in starch molecular structure and reactions among flour components leading to more stable structures, thus affecting their pasting behavior, thermal properties and in vitro digestion.     

Effect of A- and B-granules of wheat starch on Chinese noodle quality

To investigate the effect of A- and B-type granules of wheat starch on noodle quality, the fractionation and reconstitution method was used to prepare noodles with five different ratios of A-to B-granules (100A-0B, 75A-25B, 50A-50B, 25A-75B, 0A-100B). The pasting and swelling properties of reconstituted flours and the microstructure of noodles observed under a confocal laser scanning microscope (CLSM) indicated that there were at least two aspects were responsible for the changes in noodle quality. First, the water distribution, texture and cooking quality of noodles were influenced by the different physicochemical properties of A- and B-granules; and second, the gluten structure in noodles was altered by the granule size distribution, which further led to a difference in noodle quality. In general, with increasing number of B-granules, the A₂₂ (the proportion of less immobilized water) of raw noodles and the hardness, resilience and chewiness of cooked noodles increased first and then decreased, while the cooking loss, water absorption and protein loss showed the reverse trend. Raw noodle samples containing 50A-50B had the minimum T₂₂ (less immobilized water) but the maximum A₂₂ and, when cooked, had the greatest hardness, chewiness and resilience and the least cooking loss (6.6%) and water absorption (166.1%). These results have important implications for illustrating the mechanism by which A- and B-granules affect noodle quality and guide efforts to improve noodle quality and wheat breeding.     

Effect of gliadin/glutenin ratio on pasting,thermal, and structural properties of wheat starch

Gluten-starch interactions are of specific importance during the processing of cereal-based products. However, the mechanisms for gluten-starch interactions have not been illuminated. The effects of various gliadin/glutenin (gli-glu) ratios (0:10, 3:7, 5:5, 7:3, and 10:0) on the pasting, thermal, and structural properties of wheat gluten-starch mixtures were investigated. The peak, through, and final viscosities were obviously decreased, and the setback value initially increased and then decreased with increasing gli-glu ratios during the rapid viscosity analysis (RVA). Differential scanning calorimetry showed that the enthalpy changes increased with increasing gli-glu ratios. Thermogravimetric analysis showed a slight increase in the degradation temperature of the mixtures as the gli-glu ratio increased, although it was still lower than that of wheat flour. However, there was no significant difference in the weight loss among different gli-glu ratios. Rheometer-Fourier transform infrared (FTIR) spectroscopy showed that the C-6 peak at 996 cm⁻¹ for all the samples was displaced or disappeared due to the hydrogen bond fracture caused by water molecules entering the starch granules. It was also found that the absorption peak in amide II of gli-starch was more obvious than that of glu-starch. The CLSM obviously described the change structure of mixtures with different gli-glu ratio during starch gelatinizaton. By studying the changes in gluten protein components and how they affected the thermal and structural properties of starch, a simple model was proposed to describe the gelatinization process of the mixtures with different ratios of gli-glu and briefly describe the interactions between starch and wheat gluten components. Optimization of the proportion of protein components in wheat flour will enable greater control over the structural characteristics and elasticity of wheat food products.     

Physicochemical properties and amylopectin fine structures of A- and B-type granules of waxy and normal soft wheat starch

This work fractionated waxy and normal wheat starches into highly purified A- and B-type granule fractions, which were representative of native granule populations within parent native wheat starches, to accurately assess starch characteristics and properties of the two granule types. Wheat starch A- and B-type granules possessed different morphologies, granule specific surface area measurements, compositions, relative crystallinities, amylopectin branch chain distributions, and physical properties (swelling, gelatinization, and pasting behaviors). Within a genotype, total and apparent amylose contents were greater for A-type granules, while lipid-complexed amylose and phospholipid contents were greater for B-type granules. B-type (relative to A-type) granules within a given genotype possessed a greater abundance of short amylopectin branch chains (DP_n < 13) and a lesser proportion of intermediate (DP_n 13–33) and long (DP_n > 33) branch chains, contributing to their lower relative crystallinities. Variation in amylose and phospholipid characteristics appeared to account for observed differences in swelling, gelatinization, and pasting properties between waxy and normal wheat starch fractions of a common granule type. However, starch granule swelling and gelatinization property differences between A- and B-type granules within a given genotype were most consistently explained by their differential amylopectin chain-length distributions.     

Dough rheological properties and noodle-making performance of non-waxy and waxy whole-wheat flour blends

Dough rheological properties and noodle-making performance of non-waxy whole-wheat flour (WWF) with partial- or full-waxy (PW- or FW-) WWF substitution were studied. The substitution levels were 0, 250, 500, 750, and 1000 g/kg, respectively. FW-WWF reduced the peak viscosity and pasting temperature of WWF blends as its substitution level was increased due to its higher proportions of B-type starch granules and short amylopectin chains, while PW-WWF increased peak viscosity with the increasing substitution level because of its higher amylopectin content. As demonstrated by farinograph and rheometer measurements, FW-WWF interfered with gluten development because of the increased competition for water by arabinoxylans and amylopectin; however, PW-WWF enhanced dough strength due primarily to its increased protein content. Consequently, FW-WWF showed a detrimental effect on cooked noodle texture as the cooked noodle hardness was reduced by 50% at the 1000 g/kg substitution level. In contrast, PW-WWF enhanced noodle integrity and elasticity by increasing cooked noodle cohesiveness and resilience by 10.1% and 14.8%, respectively, at the 1000 g/kg substitution level. The results suggest that with waxy WWF substitution, the changes in starch composition, arabinoxylans, and protein content could modify the interactions among flour components and influence the quality characteristics of noodle products.     

Effects of transglutaminase on the rheological and noodle-making characteristics of oat dough containing vital wheat gluten or egg albumin

Incorporating exogenous proteins into food production is a common practice for improving processing characteristics. In the present study, oat dough containing 15% (w/w, blends of protein-oat flour basis [POB]) vital wheat gluten (VWG) or 15% (w/w, POB) egg albumin (EA) was used to produce noodles with or without gluten (i.e., gluten-free). The rheological and noodle-making characteristics of oat dough containing exogenous proteins and the effects of added transglutaminase (TGase) were examined. The results indicate that the extent of TGase’s modification of the thermomechanical and dynamic rheological characteristics (G′ and G″) is dependent on the source of exogenous proteins in the oat dough. By adding 1.0% (w/w, POB) TGase, the cooking qualities of the resulting noodles (i.e., those containing VWG and EA) were significantly elevated with lower cooking loss; the elasticity of both types of noodles increased. The effects of TGase in different dough systems were analyzed by SDS-PAGE. In oat dough prepared with VWG, TGase was shown to catalyse the cross-linking of both oat protein and gluten protein; however, oat protein acted as the only substrate of TGase in the noodles that had been prepared with EA.     

Effects of heat,drought and their combined effects on morphological structure and physicochemical properties of rice (Oryza sativa L.) starch

High temperature (HT) and drought stress (WS) severely affect rice quality by altering the starch structure in rice. The morphological and physicochemical properties of starches isolated from two rice varieties grown under three stress treatment (HT, WS and WS + HT) during the grain filling stage were investigated. The results showed that WS increased amylose content (AC%) and the proportion of large starch granules (LSG) and made the surface of the starch granule smooth and flat. As a result, a lower relative crystallinity, surface order, swelling power, setback viscosity and gelatinization enthalpy were caused. HT decreased AC% and milled rice rate, but increased chalky rice rate, the number of LSG and the large air space and pits on the surface of the starch granules. As a result, a higher relative crystallinity, surface order, swelling power, setback viscosity and gelatinization enthalpy were caused. Similar results were observed under the treatment of WS + HT, indicating that there is a mild antagonistic effect on rice starch when the HT and WS occur simultaneously.     

Study of the mechanism of improvement due to waxy wheat flour addition on the quality of frozen dough bread

Waxy wheat flour (WWF) was substituted for 10% regular wheat flour (RWF) in frozen doughs and the physicochemical properties of starch and protein isolated from the frozen doughs stored for different time intervals (0, 1, 2, 4 and 8 weeks) were determined to establish the underlying reasons leading to the effects observed in WWF addition on frozen dough quality. Using Nuclear Magnetic Resonance (NMR), Differential Scanning Calorimeter (DSC) and X-ray Diffraction (XRD) among others, the gluten content, water molecular state, glutenin macropolymer content, damaged starch content, starch swelling power, gelatinization properties, starch crystallinity and bread specific volume were measured. Compared to RWF dough at the same frozen storage condition, 10% WWF addition decreased dry gluten and glutenin macropolymer contents and T₂₃ proton density of frozen dough, but increased the wet gluten content, T₂₁ and T₂₂ proton density. 10% WWF addition also decreased damaged starch content, but increased starch swelling power, gelatinization temperature and enthalpy, crystallinity of starch and bread specific volume of frozen dough. Results in the present study showed that the improvement observed due to WWF addition in frozen dough bread quality might be attributed to its inhibition of redistribution of water molecules bound to proteins, increase in damaged starch content and decrease in starch swelling power.     

Influence of environmental temperature during grain filling period on granule size distribution of rice starch and its relation to gelatinization properties

High temperature (HT) is the major environmental factor affecting grain starch properties of cooking rice cultivars. However, little information has been available on the effect of environmental temperature on the starch granule size distribution of rice grains. In this paper, five indica rice genotypes, including the wild type (9311) and its four mutants differing in amylose content (AC), were used to investigate the effect of environmental temperature on the starch granule size distribution, as well as its relation to AC and gelatinization properties of rice starch. Two temperature treatments (HT and NT) at filling stage were imposed to rice plants under the controlled temperature chambers. The result showed that HT increased the average diameter of starch granules and enhanced the proportion of large starch granules (LSG, D > 2.6 μm) by number, volume and surface area, respectively. However, influence of HT on GT and starch granule size distribution was relatively independent of their alteration in AC level for different rice genotypes. Therefore, HT-induced increase in the average diameter of starch granules and LSG percentage was strongly responsible for the higher starch gelatinization temperature and inferior cooked palatability of HT-ripening rice grains, which be not inherently associated with their varying AC level.     

Partial least-squares regression study of the effects of wheat flour composition,protein and starch quality characteristics on oil content of steamed-and-fried instant noodles

Steamed-and-fried instant noodles represent a fast growing product category; however, concern has been raised about high residual oil content by both consumers and manufacturers. To understand how wheat flour characteristics affect the oil content of instant noodles, samples of five Iranian hexaploid landraces, five US/Canadian samples, and seven local commercial wheat flours were analyzed for composition, protein and starch quality, and noodle-making quality. Partial least-squares regression (PLS) analysis between composition, protein quality properties and wheat starch gel properties (independent variables, X) and oil content of instant noodles (dependent variable, Y) resulted in a model that could explain 76.3% of the variability with a cross-validated correlation coefficient of 58.2%. PLS regression coefficient analysis showed that protein content and protein quality were the most important factors, and were negatively correlated with oil content of instant noodles. Starch quality properties, gel hardness, gumminess and chewiness as well as pasting properties were other important contributors. Starch gel hardness, gumminess and chewiness were positively correlated with oil content of instant noodles, while pasting properties were negatively correlated.     

Characterization of sorghum grain and evaluation of sorghum flour in a Chinese egg noodle system

Sorghum is a gluten free grain that has potential to be used as an alternative to wheat flour for the Celiac Sprue market. There are thousands of sorghum lines that have not been characterized for grain, flour or end product quality. The objective of the research was to gain an understanding among grain sorghum quality factors and Chinese egg noodles quality. Four sorghum hybrids were characterized and evaluated for kernel characteristics, proximate analysis, flour composition and end product in a Chinese egg noodle system. Kernel size and weight affected the flour particle size and the amount of starch damage. Flour with fine particle size and high starch damage conferred noodles with high firmness and high tensile strength. Water uptake was highest for flour with smaller particle size (38 μm at 50% volume) and higher starch damage (6.14%). Cooking losses for all samples were below 10%. Starch of particle size <5 μm (C-type) contributed to firmer and higher tensile strength noodles. Water absorption was significantly affected by flour particle size, starch particle size and starch damage. Through control of sorghum grain and flour quality characteristics it is possible to manufacture a Chinese egg noodle with good physical attributes.