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1.
The rheological characteristics of hydrated cv. Obelisk and Katepwa glutens, with poor and good baking potential, respectively, were studied at small and large deformations. Dynamic (oscillatory) measurements at small deformations over a frequency range of 0·03 to 3 rad/s showed that cv. Katepwa gluten had a higher dynamic modulus and a lower loss tangent than cv. Obelisk gluten. Overmixing resulted in increases in the dynamic moduli of both glutens. Measurements at different water contents indicated that the lower dynamic moduli at higher water contents resulted mainly from a concentration effect and were not due to water acting as a plasticiser. The apparent biaxial extensional viscosities of the glutens were determined by uniaxial compression of cylindrically shaped test pieces at various cross-head speeds. This proved to be a very useful method of providing information about the rheological behaviour of glutens at large deformations as a function of different strain rates. At every biaxial strain rate tested, the apparent biaxial extensional viscosity of cv. Katepwa gluten was higher than that of cv. Obelisk gluten. A thin layer of biaxially extended gluten showed a higher resistance to further biaxial extension than a less biaxially extended, thicker layer. Cv. Katepwa gluten exhibited this strain hardening behaviour to a greater extent than cv. Obelisk gluten. Possible consequences for baking performance are discussed.  相似文献   

2.
The dynamic rheological properties of glutens and gluten fractions (gliadin and glutenin) of two U.K.-grown wheat cultivars, Hereward and Riband, having good and poor bread quality, respectively, were studied. Gluten and glutenin doughs from cv. Hereward had higher G' and lower tan δ values than those from cv. Riband at all frequencies studied. A more pronounced difference in G' and tan δ was observed between the glutenin doughs of the two wheats than between their respective gluten doughs. The rheological properties, i.e. G' and tan δ values, of gliadin doughs were similar for both wheats. Varying the gliadin/glutenin ratio by adding the isolated gliadin or glutenin sub-fractions to the parent glutens showed that the G' values decreased and the tan δ values increased as the gliadin/glutenin ratio was increased for both cultivars, indicating a considerable decrease in elasticity as the gliadin/glutenin ratio increased. The decrease in G' may be attributed to a plasticising effect of gliadin and ‘interference’ of gliadin with glutenin-glutenin interactions. The reduction in G' was much more pronounced when the gliadin/glutenin ratio was increased between 0.15 and 1.0 than between 1.0 and above. Gluten from cv. Hereward had higher G' and lower tan δ values than cv. Riband gluten at all gliadin/glutenin ratios, indicating that cv. Hereward gluten had greater elastic character than cv. Riband gluten. Although significant effects of other non-protein hydrocolloid components cannot be discounted, these observations are consistent with the view that the viscoelasticity of the glutenin sub-fraction of gluten and differences in the ratio of gliadin to glutenin are the main factors governing inter-cultivar differences in the viscoelasticity of wheat gluten.  相似文献   

3.
The effect of salt concentration used in preparing gluten, on the subsequent dissolution of gluten in water, was examined. Flour from a Canadian hard red spring wheat cultivar, Katepwa, was used to prepare glutens using three different solvents, i.e. distilled deionized water (DDW), 0·2% NaCl solution and 2% NaCl solution. The isolated wet glutens were extracted sequentially with DDW, providing four water soluble fractions and an insoluble residue. The amount of protein in each fraction was determined and respective compositions were assessed electrophoretically under reducing and non-reducing conditions. Surprisingly, DDW extracts of gluten prepared with 2% NaCl contained almost all the gliadins, except some ω-gliadin components, and most of the polymeric glutenin. For the gluten prepared with 0·2% NaCl, most of the gliadin, but only a small portion of glutenin, was extracted. For gluten prepared with DDW, only part of the gliadins and almost no glutenin was extractable with water. The DDW solubilities of gluten proteins prepared in DDW, 0·2% NaCl and 2% NaCl were 27, 52, and 85%, respectively, after four sequential extracts with DDW. The large increases in the solubility of gliadin and glutenin proteins in DDW when the gluten is prepared in salt solution (after removal of most of the salt) can be explained on the basis of a salt-induced conformational change of the proteins, which renders water a more effective solvent.  相似文献   

4.
The functional properties of wheat are largely dictated by composition and interactions of the gluten proteins. All flours contain gliadin and glutenin, but produce baked products of varying quality, which provides evidence that gluten proteins from different wheats possess different properties. A common method to study differences in gluten properties, which is utilized in this study, is fractionation/reconstitution experiments to understand how various gliadin to glutenin ratios and how fractions from different wheat sources affect gluten aggregation properties. Gliadin and glutenin from a vital wheat gluten were fractionated with 70% ethanol and reconstituted at various gliadin to glutenin ratios. Gliadin and glutenin from a Canadian eastern soft, eastern hard and western hard wheat (14% moisture) were fractionated and substituted between flours at the native gliadin to glutenin ratio. Gluten combinations were evaluated with a Gluten Peak Tester at constant temperature and mixing. Varying gliadin to glutenin ratio showed that 50:50 is optimal for fast gluten aggregation while amount of glutenin dictates strength. Substitution experiments showed that replacing good quality gluten fractions with those from a lower quality wheat decreases gluten quality, and vice versa. Data also showed that cultivar specific differences in gliadin and glutenin are more important in dictating gluten strength (torque), while gliadin to glutenin ratio dictates aggregation time (PMT) independent of the source of fractions. The study demonstrated the ability of the improved method to evaluate gluten aggregation by controlling for all variables except the one being tested. The data also revealed information about gluten aggregation properties never before seen.  相似文献   

5.
The functional properties of wheat are largely dictated by composition and interactions of the gluten proteins. All flours contain gliadin and glutenin, but produce baked products of varying quality, which provides evidence that gluten proteins from different wheats possess different properties. A common method to study differences in gluten properties, which is utilized in this study, is fractionation/reconstitution experiments to understand how various gliadin to glutenin ratios and how fractions from different wheat sources affect gluten aggregation properties. Gliadin and glutenin from a vital wheat gluten were fractionated with 70% ethanol and reconstituted at various gliadin to glutenin ratios. Gliadin and glutenin from a Canadian eastern soft, eastern hard and western hard wheat (14% moisture) were fractionated and substituted between flours at the native gliadin to glutenin ratio. Gluten combinations were evaluated with a Gluten Peak Tester at constant temperature and mixing. Varying gliadin to glutenin ratio showed that 50:50 is optimal for fast gluten aggregation while amount of glutenin dictates strength. Substitution experiments showed that replacing good quality gluten fractions with those from a lower quality wheat decreases gluten quality, and vice versa. Data also showed that cultivar specific differences in gliadin and glutenin are more important in dictating gluten strength (torque), while gliadin to glutenin ratio dictates aggregation time (PMT) independent of the source of fractions. The study demonstrated the ability of the improved method to evaluate gluten aggregation by controlling for all variables except the one being tested. The data also revealed information about gluten aggregation properties never before seen.  相似文献   

6.
The prolamin composition of gluten was shown to have a major influence on network viscoelasticity and on breadmaking quality, but its effect on films mechanical properties has never been investigated. Two glutens from different wheat varieties (NSA 2 and Farak) were compared. The prolamin composition of these glutens was quite different, Farak variety being richer in unextractable glutenins. These differences induced contrasting functional properties (alveographic analysis and mixing properties), featuring a strong (Farak) and a weak (NSA 2) gluten. Films were made by casting using several dispersing agents. The influence of protein composition due to genotype was very weak and was overwhelmed in all cases by the process influence. The weak influence of prolamin composition was further investigated by fractionating a commercial gluten into gliadin-rich and glutenin-rich fractions. Films were made from these fractions. Their mechanical properties revealed that, at similar composition, glutenin films were more resistent than gluten and gliadin films. However, a study of the plasticiser influence on films mechanical properties showed that these differences could be totally shielded by modifying the plasticiser amount in the film. Finally, it was possible to draw a logarithmic relationship between stress and strain, this relationship being convenient for the whole gluten as well as for the fractions.  相似文献   

7.
Fractionation and reconstitution/fortification techniques were utilised to study the role of gluten in Arabic bread. Glutens from two wheat cultivars of contrasting breadmaking quality were fractionated by dilute HCl into gliadin and glutenin. Gluten, gliadin and glutenin doughs from the good quality flour had higher G ′ and lower tan δ values than those from the poor quality flour at all the frequencies examined. Interchanging the gliadin and glutenin fractions between the reconstituted flours showed that the glutenin fraction is largely responsible for differences in the breadmaking performance. Fortification of an average quality flour with the gliadin and glutenin fractions from the poor and good quality flours, at the levels of 1% and 2% (protein to flour mass), induced marked differences in the mechanical properties of bread. The resilience of the loaves was not adversely affected by the addition of gliadins and increased, with a concomitant significant (p<0·05) improvement in quality, at the 2% level of fortification with gliadins from the good quality flour. Addition of glutenin resulted in loaves with leather-like properties that became particularly apparent at the higher level of fortification; the observed deterioration in quality paralleled the increase in the elastic character of the doughs. It is suggested that highly-elastic doughs are not compatible with the rapid expansion of gases at the high-temperature short-time conditions employed in the baking of Arabic bread and that there exists a threshold in dough elasticity beyond which a rapid decline in quality takes place.  相似文献   

8.
Large-scale Separation of Gliadins and their Bread-making quality   总被引：1，自引：0，他引：1  
A separation procedure was developed using S-Sepharose cation exchange chromatography under mildly acidic conditions to establish the effect of 70% (v/v) ethanol extractable proteins on bread-making quality. The separation of a 70% (v/v) ethanol extract of gluten was scaled up successfully from 3 mg to 60 g protein. The use of denaturing and dissociating agents, such as urea or guanidine-HCl, was unnecessary. The pilot-scale fractionation yielded five fractions that were bound to, and eluted from, the column. The fractions differed in gliadin composition as evidenced by lactate-PAGE, SDS-PAGE and RP-HPLC. The fractions were virtually free of lipid. Isolated fractions were evaluated for their effects on bread-making quality using a pan loaf baking test. The unbound fraction (D) contained lipids, mainly mono- and digalactosyldiacylglycerols, and it increased (cv. Obelisk flour) or decreased (cv. Camp Rémy flour) loaf volume at additions of up to 0·5% on flour weight. At higher levels of addition it had a strong negative effect on loaf volume. The unfractionated extract (containing some fraction D) or the recombined fractions improved loaf volume. All individual fractions improved loaf volume, but to different extents. For four out of five fractions the improvement corresponded to the statistical prediction of loaf volume by RP-HPLC gliadin peak areas.  相似文献   

9.
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.  相似文献   

10.
The dynamic rheological behaviours of mixtures of glutenin fractions extracted from wheat cultivar Hereward were investigated as a function of the relative concentration of high to low molecular weight glutenin concatenations. Time-temperature superposition could be applied to both the mixtures and to the total gluten, as long as heat-treated samples were distinguished from unheated samples. The ratio of high to low molecular weight concatenations was found to be very important for the rheological behaviour of the network. High molecular weight fractions promoted the network properties of the mixture, as could be seen from the presence of a plateau in the rheological spectrum. Low molecular weight fractions gave rise to a plasticizing effect as indicated by their narrowing effect on the width of the plateau region in the rheological spectrum. Upon heating, the modulus increased over the full range of frequencies, as for single fractions. This increase indicated that a thermal association occurred in the concatenations at temperatures around 40 °C. As a result of heating, the transition zone became apparent in the spectrum at high frequencies. The slopes of the loss modulus G” in the transition zone were found to be higher for mixtures rich in low molecular weight concatenations. The effect of the relative abundance of each fraction on the rheological characteristics of the mixtures was summarized in a number of simple rheological blending rules for the small-deformation rheological properties of glutenin.  相似文献   

11.
The effects of addition of purified total gliadin and its subgroups (α-, β-, γ- and ω-gliadins) on the dynamic rheology of gluten were investigated. The frequency sweeps of gluten with added α-, β-, γ- and ω2-gliadins showed unexpected increases in the magnitude of G′ and G′′, suggesting stiffening of the native gluten. Conversely, a reduction in the magnitude of G′ and G′′ occurred upon addition of the total gliadin fraction and the ω1-gliadin, implying softening of the gluten. Addition of individual gliadin fractions increased the values of slope log G′ vs log frequency, suggesting increased concentrations of uncrossed-linked material compared with the native gluten. There were significant differences in the slope values for individual gliadin fractions. The increasing order of slopes for different gliadins was: β- >γ- >α- =ω1>ω2, indicating that glutens containing ω- and α- gliadins are relatively less crossed-linked than those containing β- and γ-gliadins. The dynamic moduli, G′ and G′′, of cv. Hereward gluten showed significant positive relationships with Mixograph parameter peak dough resistance (PDR), and loaf volume for gliadin subgroups added to cv. Hereward flour.  相似文献   

12.
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.  相似文献   

13.
The mechanical properties of flour–water doughs and hydrated gluten of different wheat cultivars were determined. Measurements were performed at small deformations (dynamic measurements) as well as at large deformations (biaxial extension measurements). Results of dynamic measurements of flour doughs related poorly to breadmaking quality. For hydrated gluten doughs, all having the same water content, it was found that glutens from wheat cultivars with good baking quality had higher values for the storage modulus,G, and lower values for the loss tangent. The relevant type of deformation around an expanding gas bubble is biaxial extension. Wheats with a good baking performance exhibited greater strain hardening and greater extensibility. The differences in strain hardening observed at 20 °C were also present at 55 °C. No clear effects of NaCl or emulsifiers on the biaxial extension properties of flour dough were found. Extensograms as well as Alveograms from the flour doughs showed that, in general, good baking flours exhibited stronger resistance to extension and a greater extensibility, but differences found were not directly related to the results of the baking tests. The results indicate that the baking performance of dough is related to a combination of at least three different rheological characteristics.  相似文献   

14.
Rheological properties of gluten from three biscuit wheat cultivars (Triticum aestivum, L., cv. Reaper, Ritmo, Encore) were studied. The cultivars were grown in two seasons (1997–1999) with three different nitrogen levels, and nitrogen fertiliser was applied using three different strategies. Protein and gluten contents were significantly affected by the N level (P<0.001), but inter-cultivar differences were only significant in 1999, when growing conditions were restricted by environmental factors. The viscoelastic properties of gluten were characterised by creep recovery and oscillation testing. The results showed a significant inter-cultivar effect (P<0.001), with an additional effect from the N level (P<0.001). Increasing levels of nitrogen fertiliser increased the viscous properties of gluten, through an increase of maximum strain and recovery strain, and through a decrease of the storage (G′) and loss modulus (G′′), whereas the phase angle, δ, increased. This increase in viscous behaviour is suggested to be attributed to a higher gliadin/glutenin ratio in the gluten. The fertiliser application strategy did not influence the rheological properties significantly. Thus, high N fertiliser application in biscuit wheat cultivation may be beneficial to obtain rheological properties, which are suitable for biscuit making.  相似文献   

15.
The nutritive value of various protein fractions was studied. Fractions 2S and 12S from rapeseed, 2S, 7S and 11S from soybean were obtained by dissolution in ammonium sulfate solutions. Albumin-globulin, gluten, glutenin and gliadin fractions from wheat were obtained by dissolution in salted water (albumin-globulin), acetic acid (glutenin) and alcohol (gliadin). Liveweight gains, protein efficiency ratio (PER) and apparent digestibility coefficient (ADC) were used as measures of the nutritive value. The protein fractions had a lower nutritive value than the unfractionated proteins except for the albumin-globulin fraction of wheat which had a nutritive value higher than that of the unfractionated wheat protein. PER obtained with the rapeseed 2S and 12S fractions were 2.49 and 2.21, respectively, as compared to 2.64 for unfractionated rapeseed. With soybean fractions, PER were 0.92 for 2S, — 0.007 for 7S and 1.47 for 11S, as compared to 2.19 for the original protein. The wheat albumin-globulin fraction gave a PER of 2.78, as compared to 1.45 for the unfractionated wheat protein. Gluten, glutenin and gliadin fractions had a lower PER than that of unfractionated wheat protein. ADC of all fractions were higher than those of the original proteins. The difference in liveweight gains and PER observed between protein fractions can be partially explained on the basis of the essential amino acid content.  相似文献   

16.
Glutens from poor breadmaking quality wheat, cv. Riband, had a higher SDS extractability than glutens from good quality cv. Hereward. Heating of gluten, especially above 70 °C, caused a reduction in the amount of SDS-extractable gluten proteins. Treatment of gluten with redox additives (ascorbic acid, potassium bromate or glutathione) affected extractability, being highest for bromate treated glutens. The SH content of gluten was lower for poor breadmaking Riband and heating resulted in greater decrease in SH content of gluten from good breadmaking Hereward. Hereward gluten had a higher SS content than Riband. The alteration of SS content on heating was not significant and may indicate the heat-induced involvement of non-covalent interactions. SDS-PAGE revealed that oxidants, especially bromate, affect polypeptide composition leading to a more heat stable/tolerant protein structure.  相似文献   

17.
水氮互作对小麦籽粒蛋白质组分和品质的影响   总被引：1，自引：0，他引：1  
为了给强筋小麦高产优质高效栽培提供理论依据,以高产强筋小麦品种济麦20为材料,研究了施氮量和灌溉量对小麦籽粒蛋白质组分和品质的影响.结果表明,施氮量由120 kg*ha-1(N1)增加至240 kg*ha-1(N2),籽粒蛋白质含量、清蛋白和球蛋白含量增加,(醇溶蛋白+麦谷蛋白含量)/(清蛋白+球蛋白含量)比值(谷醇/清球比值)降低,面团稳定时间缩短.同一施氮量条件下,由不灌水(W0)到灌2水(W1),籽粒蛋白质含量增加,谷醇/清球比值降低,面团稳定时间缩短;由灌2水(W1)到灌3水(W2)和5水(W3),籽粒蛋白质含量降低,蛋白质组分中清蛋白和球蛋白含量升高,醇溶蛋白和麦谷蛋白含量降低,谷醇/清球比值降低,面团稳定时间亦缩短.以上结果表明,在本试验条件下,增加施氮量和灌水量导致面团稳定时间缩短,原因是清蛋白和球蛋白占总蛋白含量的比例,即谷醇/清球比值降低.  相似文献   

18.
The breadmaking quality of wheat is affected by the composition of gluten proteins and the polymerisation of subunits that are synthesised and accumulated in developing wheat grain. The biological mechanisms and time course of these events during grain development are documented, but not widely confirmed. Therefore, the aim of this study was to monitor the accumulation of gluten protein subunits and the size distribution of protein aggregates during grain development. The effect of desiccation on the polymerisation of gluten proteins and the functional properties of gluten were also studied. The results showed that the size of glutenin polymers remained consistently low until yellow ripeness (YR), while it increased during grain desiccation after YR. Hence, this polymerisation process was presumed to be initiated by desiccation. A similar polymerisation event was also observed when premature grains were dried artificially. The composition of gluten proteins, the ratios of glutenin to gliadin and high molecular weight-glutenin subunits to low molecular weight-glutenin subunits, in premature grain after artificial desiccation showed close association with the size of glutenin polymers in artificially dried grain. Functional properties of gluten in these samples were also associated with polymer size after artificial desiccation.  相似文献   

19.
Flour samples of 14 wheat cultivars previously characterised by rheological measurements and by baking tests on a micro-scale (Kieffer et al.: Journal of Cereal Science27 (1998) 53–60) were analysed for the relative amounts of gluten protein types using a combined extraction/HPLC procedure. Regression analysis was used to find relations between wheat properties and protein quantities. The results indicated that the maximum resistance of dough and gluten and the gluten index were strongly dependent on the quantity of glutenin subunits (GS) in flour; additionally they were influenced by the ratio of gliadin to glutenin subunits. Within the family of glutenin proteins, the correlation coefficients for high-molecular-weight (HMW) and low-molecular-weight (LMW) GS were in a similar range, but twice the amount of LMW GS was necessary to get the same resistance as with HMW GS. Among HMW GS, the contribution of x-type GS was more important than those of y-type GS. The extensibility of dough and gluten was mainly dependent on the ratio of gliadin to total glutenin subunits, to HMW GS and LMW GS. Dough development time showed the highest correlation with total HMW GS and x-type HMW GS. Bread volume was influenced by the total amount of gluten protein more than by the amount of protein in different groups or of different types, probably because of the rather low range of flour protein content (8·7–12·0 %) within the set studied. Significant differences between gliadins and glutenins with respect to their effects on bread volume could not be detected. The correlation between bread volumes and the quantity of gluten proteins was higher, when dough was mixed to optimum.  相似文献   

20.
小麦贮藏蛋白特性及其遗传转化   总被引：13，自引：7，他引：13  
小麦籽粒贮藏蛋白由醇溶蛋白和谷蛋白组成。醇溶蛋白在组成上以单体形式存在 ,具有高度的异质性和复杂性。它决定小麦面筋的粘性。谷蛋白是由多个亚基组成的高分子聚合体 ,决定面筋的弹性。它可分为低分子量谷蛋白亚基和高分子量谷蛋白亚基 (HMW- GS)。HMW- GS具有相似的分子结构 ,即由中央重复序列、无重复的 N端和 C端组成。HMW- GS对小麦烘烤品质起着决定性作用 ,但因 HMW- GS类型不同而对加工品质的贡献大小各异。许多 HMW- GS基因已被揭示。实践证明 ,利用基因枪法 ,将 HMW- GS基因导入普通小麦的细胞核内 ,能够达到改良小麦烘焙品质的目的。随着分子生物学技术的不断发展 ,可望从营养和加工角度来改良小麦品质的特性  相似文献   

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