Changes in the content of free sulphydryl groups during postharvest wheat and flour maturation and their influence on technological quality

The main aim of this study was to determine the changes in free sulphydryl content during postharvest wheat and flour maturation. The content of free sulphydryl groups was determined from wet gluten over 50 days of wheat postharvest maturation and over 14 days of flour maturation by varying incubation temperatures (30 and 37 °C) and incubation times (0, 45, 90 and 135 min). The amount of free sulphydryl groups increased during postharvest wheat and flour maturation as well as with the increase in temperature and gluten incubation time. The additional aim of this study was to find the interrelation between the content of free sulphydryl groups and selected parameters of technological quality by means of Principal Component Analysis. During wheat/flour maturation, the strengthening of protein structure was observed manifested by the increase in gluten index and Mixolab protein network weakening (C2), and changes in dough resistance as well. The incubation temperature of 37 °C affected the weakening of protein structure manifested by the decrease in gluten index and resistance, and increase in extensibility. Strong differentiation of examined varieties in terms of selected quality indicators was observed upon pre-defined maturation period, probably due to the expression of their intrinsic properties.     

Differential accumulation of sulfur-rich and sulfur-poor wheat flour proteins is affected by temperature and mineral nutrition during grain development

Hard red spring wheat (Triticum aestivum cv Butte86) was grown under controlled environmental conditions and grain produced under 24/17 °C, 37/17 °C or 37/28 °C day/night regimens with or without post-anthesis N supplied as NPK. Flour proteins were analyzed and quantified by differential fractionation and RP-HPLC, and endosperm proteins were assessed by two-dimensional gel electrophoresis (2-DE). High temperature or NPK during grain fill increased protein percentage and altered the proportions of S-rich and S-poor proteins. Addition of NPK increased protein accumulation per grain under the 24/17 °C but not the 37/28 °C regimen. However, flour protein composition was similar for grain produced with NPK at 24/17 °C or 37/28 °C. 2-DE of gluten proteins during grain development revealed that NPK or high temperature increased the accumulation rate for S-poor proteins more than for S-rich proteins. Flour S content did not indicate S-deficiency, however, and addition of post-anthesis S had no effect on protein composition. Although, high-protein flour from grain produced under the 37/28 °C regimen with or without NPK had loaf volumes comparable to flour produced at 24/17 °C with NPK, mixing tolerance was decreased by the high temperature regimen.     

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.     

The impact of heating and cooling on the physico-chemical properties of wheat gluten–water suspensions

The rapid visco analysis (RVA) system was used to measure rheological behaviour in 20% (w/v) gluten-in-water suspensions upon applying temperature profiles. The temperature profiles included a linear temperature increase, a holding step, a cooling step with a linear temperature decrease to 50 °C, and a final holding step at 50 °C. Temperature and duration of the holding phase both affected RVA viscosity and protein extractability. Size-exclusion and reversed-phase HPLC showed that increasing the temperature (up to 95 °C) mainly decreased glutenin extractability. Holding at 95 °C resulted in polymerisation of both gliadin and glutenin. Above 80 °C, the RVA viscosity steadily increased with longer holding times while the gliadin and glutenin extractabilities decreased. Their reduced extractability in 60% ethanol showed that γ-gliadins were more affected after heating than α-gliadins and ω-gliadins. Enrichment of wheat gluten in either gliadin or glutenin showed that both gliadin and glutenin are necessary for the initial viscosity in the RVA profile. The formation of polymers through disulphide bonding caused a viscosity rise in the RVA profile. The amounts of free sulphydryl groups markedly decreased between 70 and 80 °C and when holding the temperature at 95 °C.     

Characteristics of enzymatic hydrolysis of thermal-treated wheat gluten

Effect of thermal treatment at 50–90 °C on wheat gluten hydrolysis by papain was evaluated in this study. Thermal treatment decreased the amount of sodium dodecyl sulfate (SDS) extractable protein. The treatments at 80 and 90 °C had a strong impact on protein extractability. Thermal treatment for 30 min resulted in a significant reduction in SDS extractable glutenin level in wheat gluten. A significant drop in free sulphydryl level was found in wheat gluten treated at 70 °C for 30 min. It indicated that cross-linking of glutenin through S–S occurred during thermal treatment. The treatments at 70–90 °C led to significant decreases in soluble and nitrogen level, while significant increases in peptide nitrogen amount in the hydrolysates from treated gluten were found. A time-dependent effect was observed for the changes in soluble forms of nitrogen and PN. Thermal treatment resulted in molecular mass distribution change according to gel permeation chromatography analysis. Thermal treatment significantly increased the amount of fractions with molecular mass beyond 10 K (67.2%) in the hydrolysates and greatly decreased the amounts of fractions with MM of 10–5 K and below 5 K in hydrolysates.     

Determination of volatile compounds in heat-treated straight-grade flours from normal and waxy wheats

Volatile compounds formed during heat-treatment of wheat flour influence the application of treated flour. In this study, normal and waxy hard wheat flours before and after dry-heat treatment were subjected to headspace analysis by solid-phase microextraction of volatiles followed gas chromatography–mass spectrometry (GC/MS). The untreated waxy wheat flour contained higher levels of odor-active compounds than normal wheat flour including aldehydes, alcohols, furans, and ketones. Lipid oxidation appears to play major role in producing such odor compounds. Heat treatments, depending on the severity, alter the profile of volatile compounds. Low temperature (100–110 °C) treatments effectively eliminated cereal odor (aldehyde) and did not introduce additional odors, providing a possible way to produce low-odor flours. Heat treatments at 120 °C and higher temperatures elevated the content of pyrazines, furans, and sulfur-containing compounds which together gave a roasty aroma to the flours. Considering organoleptic properties, treatments of flours at 140 °C was superior to 160 °C. The waxy wheat flour was more prone to produce odor-active compounds than normal wheat flour during the same heat treatment.     

Effect of ultraviolet irradiation on wheat (Triticum aestivum) flour: Study on protein modification and changes in quality attributes

Wheat is one of the most widely consumed cereals, and it witnesses huge variation in its physicochemical properties due to pre- and post-harvest operations, hence, it undergoes many physicochemical treatments to achieve optimum baking characteristics. In the current study, ultraviolet (UV) radiation is proposed as a green technology to modify the wheat flour characteristics. Irradiation of Wheat flour with UV-C radiation (254 nm) of different radiation power and exposure time resulted a significant change in the physicochemical properties (water-binding capacity, amylose content, reducing sugar, sulfhydryl (SH), disulfide (SS) groups level). Further, decrease in gluten content, increase in total volatile basic nitrogen (TVBN) content, and photo-induced thiol-disulfide bridge exchange was observed upon irradiation. FTIR analysis of flour, gluten and gliadin protein confirmed the modification in protein conformations upon irradiation. The β-sheet had the highest contribution in protein conformation for wheat flour, while for gluten protein powder, random coils showed the maximum contribution. The first two principal components could explain 92.55% of total variance during principal component analysis, and the gluten content was correlated positively with SS content but negatively with SH and TVBN content. This study will help researchers and industrialist to understand the interactions of UV radiation with biological material.     

Rheological properties of wheat flour processed at low levels of hydration: Influence of starch and gluten

The rheological properties of wheat flour under processing such as extrusion (with 28% moisture content, wet basis) are influenced by the molecular changes its components undergo during processing. But, there was no simple relationship between the wheat-flour characteristics and their rheological properties. In order to investigate the quantitative and qualitative effects of the individual flour components on rheological properties, model blends of wheat starch and wheat gluten with different starch/gluten ratios were studied. The effects of gluten and starch quality were also investigated by using different gluten types and by modifying the amylose content of starch, respectively. The shear viscosity of the blends, determined by capillary rheometry under controlled conditions (35% moisture content, 140 °C), was observed to be modified by both gluten and amylose content. The changes undergone by wheat gluten under these conditions were analysed by HPLC, to determine the levels of unextractable polymeric proteins, and by Lab-on-a-Chip analysis of protein composition, to follow the polymerisation of protein under processing. This study indicated that in low hydrated products in the molten state, shear viscosity is affected by the structure of the blends as determined by fluorescence microscopy and by the molecular changes occurring during processing.     

Comparison of different rice flour- and wheat flour-based butter cookies for acrylamide formation

Acrylamide (AcA) contents of different rice flour- and wheat flour-based butter cookies baked at 130 °C for 20, 55, or 90 min were investigated. AcA contents of different flour-based cookies increased with baking time. Color parameters in terms of CIE L*, b*, C*, and ΔE values showed significant opposite correlation to the AcA formation in each of the raw flour cookie. The cookies based on white rice flour had the lowest AcA contents ranging from not detectable (ND) to 204 μg/kg, followed by cookies based on brown rice flour (ND to 450 μg/kg), white wheat flour (155 μg/kg to 661 μg/kg), and whole wheat flour (306 μg/kg to 982 μg/kg). Considerably lower AcA levels were found in the rice flour-based cookies than in the wheat flour-based cookies, as well as in the milled flour-based cookies than in the whole-grain cookies. Although the flour source was considered to play a primary role in determining the AcA content, AcA content was apparently not dependent on the quantities of reducing sugars and free asparagine in the starting raw flour and cookies during baking. In summary, given its reducing potential for AcA formation, rice flour could be used in the production of cookies safe from heat-induced contaminants.     

Properties of whole grain wheat flour and performance in bakery products as a function of particle size

The aim of this study was to evaluate the effect of particle size distribution on composition, properties rheological, pasting, microstructural and baking properties of whole grain wheat flour (WGWF) of three different particles sizes (194.9 μm, 609.4 μm and 830.0 μm). The quantification of free sulfhydryl groups (-SH) of WGWF samples, together with the effects observed in the behavior of the dough and bread showed that particle size influences the functionality of the gluten network in a differentiated way. Firmer and lower breads volume compared to refined wheat flour (RF) were correlated with the quality of the gluten network. In the sample of finer particles, more pronounced adverse effects in quality (dough rheology, bread volume and texture) compared to the medium and coarse particle size sample suggests that the larger contact surface and the increased release of reactive compounds due to cell rupture interact with the gluten-forming proteins changing their functionality.     

Large deformation stress relaxation and compression-recovery of gluten representing different wheat classes

Despite the great variety of physicochemical and rheological tests available for measuring wheat flour, dough and gluten quality, the US wheat marketing system still relies primarily on wheat kernel hardness and growing season to categorize cultivars. To better understand and differentiate wheat cultivars of the same class, the tensile strength, and stress relaxation behavior of gluten from 15 wheat cultivars was measured and compared to other available physicochemical parameters, including but not limited to protein content, glutenin macropolymer content (GMP) and bread loaf volume. In addition, a novel gluten compression–relaxation (Gluten CORE) instrument was used to measure the degree of elastic recovery of gluten for 15 common US wheat cultivars. Gluten strength ranged from 0.04 to 0.43 N at 500% extension, while the degree of recovery ranged from 5 to 78%. Measuring gluten strength clearly differentiated cultivars within a wheat class; nonetheless it was not a good predictor of baking quality on its own in terms of bread volume. Gluten strength was highly correlated with mixograph mixing times (r = 0.879) and degree of recovery (r = 0.855), suggesting that dough development time was influenced by gluten strength and that the CORE instrument was a suitable alternative to tensile testing, since it is less time intensive and less laborious to use.     

河北省主推中筋小麦品种面条加工适应性研究

为了解河北省主推中筋小麦品种的面条加工适应性、筛选优质面条小麦品种,对河北省19个主推中筋小麦品种的籽粒、面粉品质性状及面条加工品质特性进行了系统检测与分析。结果表明,河北省中筋小麦品种大部分品质性状的遗传多样性较为丰富;适宜制作面条加工的小麦品种有16个,占河北主推中筋小麦品种的84.21%,其中适宜制作优质面条的小麦品种有6个;面条感官总分与中筋小麦面粉的湿面筋含量呈极显著正相关,与拉伸长度呈显著正相关,与弱化度呈显著负相关,与面条质构参数(TPA)的粘聚性和回复性均呈极显著正相关,与面条TPA的弹性、胶着性、咀嚼度和拉伸距离均呈显著正相关;面条TPA指标参数可间接反映面条的感官品质。     

Genetic responses in milling,flour quality,and wheat sensitivity traits to grain yield improvement in U.S. hard winter wheat

A rising global population necessitates continued genetic improvement of wheat (Triticum spp.), but not without monitoring of unintended consequences to processors and consumers. Our objectives were to re-establish trends of genetic progress in agronomic and milling traits using a generational meter stick as the timeline rather than cultivar release date, and to measure correlated responses in flour quality and human wheat-sensitivity indicators. Grain yield and kernel size showed stepwise increases over cycles, whereas wheat protein content decreased by 1.1 g/100 g. Reduced protein content, however, did not result in lower dough strength pertinent to bread baking. A novel method of directly testing gluten elasticity via the compression-recovery test indicated a general increase in gluten strength, whereas the ratio of total polymeric to total monomeric proteins remained stable. Also showing no change with genetic progress in yield were flour levels of gluten epitopes within the key immunotoxic 33-mer peptide. The oligosaccharide fructan, present in milled and wholemeal flours, increased with increasing grain yield potential. While yield improvement in U.S. bread wheat was not accompanied by a decline in gluten strength or systematic shift in a key wheat sensitivity parameter, the unanticipated rise in total fructans does implicate potentially new dietary concerns.     

Effect of temperature, time and wheat gluten moisture content on wheat gluten network formation during thermomolding

A plastic-like material can be obtained by thermomolding wheat gluten protein which consists of glutenin and gliadin. We studied the effect of molding temperature (130-170 °C), molding time (5-25 min) and initial wheat gluten moisture content (5.6-18.0%) on the gluten network. Almost no glutenins were extractable after thermomolding irrespective of the molding conditions. At the lowest molding temperature, the extractable gliadin content decreased with increasing molding times and moisture contents. This effect was more pronounced for the α- and γ-gliadins than for the ω-gliadins. Protein extractabilities under reducing conditions revealed that, at this molding temperature, the cross-linking was predominantly based on disulfide bonds. At higher molding temperatures, also non-disulfide bonds contributed to the gluten network. Decreasing cystine contents and increasing free sulfhydryl and dehydroalanine (DHA) contents with increasing molding temperatures and times revealed the occurrence of β-elimination reactions during thermomolding. Under the experimental conditions, the DHA derived cross-link lanthionine (LAN) was detected in all gluten samples thermomolded at 150 and 170 °C. LAN was also formed at 130 °C for gluten samples containing 18.0% moisture. Degradation was observed at 150 °C for samples thermomolded from gluten with 18.0% moisture content or thermomolded at 170 °C for all moisture contents.     

The impact of heating and cooling on the physico-chemical properties of wheat gluten–water suspensions

The rapid visco analysis (RVA) system was used to measure rheological behaviour in 20% (w/v) gluten-in-water suspensions upon applying temperature profiles. The temperature profiles included a linear temperature increase, a holding step, a cooling step with a linear temperature decrease to 50 °C, and a final holding step at 50 °C. Temperature and duration of the holding phase both affected RVA viscosity and protein extractability. Size-exclusion and reversed-phase HPLC showed that increasing the temperature (up to 95 °C) mainly decreased glutenin extractability. Holding at 95 °C resulted in polymerisation of both gliadin and glutenin. Above 80 °C, the RVA viscosity steadily increased with longer holding times while the gliadin and glutenin extractabilities decreased. Their reduced extractability in 60% ethanol showed that γ-gliadins were more affected after heating than α-gliadins and ω-gliadins. Enrichment of wheat gluten in either gliadin or glutenin showed that both gliadin and glutenin are necessary for the initial viscosity in the RVA profile. The formation of polymers through disulphide bonding caused a viscosity rise in the RVA profile. The amounts of free sulphydryl groups markedly decreased between 70 and 80 °C and when holding the temperature at 95 °C.     

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.     

Effects of vacuum mixing and mixing time on the processing quality of noodle dough with high oat flour content

The effects of different mixing parameters (vacuum mixing and mixing time) on oat (70% oat flour) and wheat noodle dough were investigated on the basis of textural properties and gluten formation. The results showed that at a vacuum degree of −0.06 MPa and mixing time of 10 min, oat and wheat dough sheets exhibited the highest resistance to extension and glutenin macropolymer (GMP) content, and had the most compact and uniform gluten network. Compared with wheat noodle dough, oat dough had lower resistance to extension, lower tightly bound water content, and higher GMP content. Microstructural examination showed that oat noodle dough had a more aggregated distribution of gluten protein compared with wheat noodle dough under the optimum mixing parameters. Furthermore, the poor binding ability of vital wheat gluten with water molecules caused the indexes of oat noodle dough to be more strongly affected by the changes in mixing parameters than wheat noodle dough.     

Susceptibility of wheat gluten to enzymatic hydrolysis following deamidation with acetic acid and sensory characteristics of the resultant hydrolysates

The effect of acetic acid and hydrochloric acid (HCl) deamidation pretreatment on the susceptibility of wheat gluten to enzymatic hydrolysis by Pancreatin and sensory characteristics of the resultant hydrolysates was investigated. At two degrees of deamidation (24% and 60%, with or without moisture-heating, respectively), wheat gluten pretreated by acetic acid deamidation was more susceptible to be hydrolyzed as evaluated by the hydrolysis degree, nitrogen solubility index, titratable acid amount and free carbohydrate content of the hydrolysates. Wheat gluten pretreated by acetic acid deamidation at a degree of 24% exhibited the highest susceptibility to enzymatic hydrolysis. Moisture-heating (121 °C, 10 min) in the deamidation pretreatment decreased the susceptibility of wheat gluten to enzymatic hydrolysis and the peptide factions of ≤3000 Da in the hydrolysates due to the formation of larger molecule weight aggregates. The hydrolysates prepared from acetic acid deamidated wheat gluten showed more intense glutamate-like and sauce-scented taste and better nutritional characteristics.     

GlutoPeak parameters of whole wheat flours for gluten quality evaluation in soft wheat breeding programs

In soft wheat breeding programs, the gluten strength of flours from specific genotypes is determined by various chemical and rheological tests. Based on such tests, the experimental wheat lines with very weak flour gluten are typically selected for the production of soft-dough biscuits, while the lines with medium gluten strength and extensibility are reserved for hard-dough biscuits. Often, the genotypes having high gluten strength are removed from such breeding programs. In the present study, the usability of the GlutoPeak tester on whole wheat flour samples was investigated for assessing the gluten strength of soft wheat breeding materials. In the study, 25 soft wheat genotypes, grown in seven locations for three years, were categorized by commonly used gluten-quality-related parameters. Based on the results of the study GlutoPeak whole wheat flour PMT values ranging from 30.0 to 50.0 s and AM values from 15.0 to 20.0 GPU were found to be suitable for soft-dough biscuit products, whereas the values between 40.0 and 60.0 s and 20.0 and 23.0 GPU were appropriate for hard-dough biscuit products. The genotypes exhibiting AM values > 24.0 GPU and PMT values > 60.0 s were judged to have too-strong gluten, and thus eliminated from the breeding program. The gluten aggregation energy (AGGEN), and the torque after the maximum torque (PM) values were only useful and applicable to flours for soft-dough products. The maximum torque (BEM) values were not effective in discriminating against the genotypes. The results of this study demonstrated that the GlutoPeak whole wheat PMT and AM parameters can be recommended as quick and accurate parameters especially for early generation screening with small-scale tests in soft wheat improvement programs.     

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.