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.     

Quality of shear fractionated wheat gluten – Comparison to commercial vital wheat gluten

The functional properties of gluten obtained with a shear-induced separation process, recently proposed by Peighambardoust et al. (2008), are compared with a commercially available vital wheat gluten. Two tests were performed. First, a relatively strong wheat flour, Soissons, was enriched with gluten protein. The resulting dough was then evaluated on its kneading performance. Second, a weak flour, Kolibri, was enriched to evaluate the baking properties. The wheat flour enriched with gluten protein obtained via the shear-induced separation process (SCG) showed comparable to improved gluten functionality relative to commercial available vital wheat gluten protein (CVWG). The differences in functionality cannot be directly related to the composition as analyzed with SE-HPLC, because the composition of the gluten materials was rather comparable. The differences in functionality may therefore be related to the different drying techniques used or to the inherent mildness of the shear-induced separation technique.     

Improvement on functional properties of wheat gluten by enzymatic hydrolysis and ultrafiltration

Four fractions (100-, 50-, 20-K and permeate) from a proteolytic hydrolysate (DH=2.8%) of wheat gluten were separated using size fractionation on ultrafiltration membranes with molecular weight cut-offs of 100, 50 and 20 kDa and their functional properties evaluated. Proteolysis led to a significant (P<0.05) increase in solubility of gluten fractions at pHs between 2–10 and a shift of the pI value from 6–7 to 5. The solubilities of 100-K, 50-K, 20-K and permeate fractions were significantly (P<0.05) improved compared with the untreated control and the hydrolysate. The 50-K fraction was superior to other three fractions for emulsion activity index between pH 2 and 10. The most stable foam was given by the 100-K fraction which showed 65.8% of initial foam while the control sample gave only 23% of foam, after 60 min resting. Foam stability decreased as the molecular mass of hydrolysate fractions decreased. Furthermore, after proteolysis, the surface hydrophobicity (H₀) of gluten increased significantly (P<0.05) compared with the control except for the permeate fraction. The highest value of H₀ was given by the 100-K fraction, followed by the 50-K, 20-K and permeate fractions. In addition, proteolysis resulted in a decrease in the storage modulus of gels.     

Effect of hydrostatic pressure and temperature on the chemical and functional properties of wheat gluten III. Studies on gluten films

Numerous gluten preparations were produced by the variation of pressure and temperature. Optimal conditions for the production of gluten films on a laboratory-scale were by suspending of gluten (1 g) in a mixture of ethanol (3 mL), glycerol (0.5 g) and conc. formic acid (10 mL), casting and drying at 40 °C. Small-scale laboratory methods for the production of gluten films by casting and moulding were developed. Film strips obtained were examined by micro-extension tests, which resulted in curves similar to extensigrams for dough and gluten and allowed the determination of the resistance to extension, extensibility and elasticity. The results demonstrated that pressure treatment of gluten in combination with variable cultivars, temperature, process parameters and additives, allow the production of films with a wide range of rheological properties – from soft and smooth to strong and hard rubber like. Finally, it was demonstrated that the addition of fibres to gluten enhanced the stability of films. Thus, high pressure treatment allows a selective modification of gluten as raw material for film production. In comparison with conventional plastic films, gluten films have considerable advantages, because they can be produced from renewable plants and they are readily biodegradable.     

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.     

Effect of extrusion treatment on enzymatic hydrolysis of wheat bran

Although, wheat bran is a good source of dietary fibre (DF), it has certain disadvantages due relatively lower levels of soluble DF. Therefore, in the current study, the effect of extrusion treatment on microstructure and enzymatic hydrolysis of wheat bran was investigated. Extrusion treatment increased fibre solubility at all process conditions and the screw speed was found to be the most effective parameter. Physicochemical properties of bran were affected from extrusion treatments. While the water-binding capacities of extruded brans were lower than that of non-extruded wheat bran, their water solubilities were higher. Enzymatic hydrolysis increased the soluble DF content of the bran samples as compared to those of respective samples at the beginning of incubation. The results showed that extrusion treatment can be used to disrupt the wheat bran microstructure and thus to increase the soluble fibre content. Enzymatic hydrolysis can also be used for increasing solubility further. The outcomes of this study can be utilized for improving the technological functionality of cereal fibres to develop high fibre ingredients for food applications.     

Elastic properties of gluten representing different wheat classes

Traditional instruments used to evaluate dough and/or gluten rheological properties do not provide unambiguous separation of elastic and viscous behaviors. Recovery after shear creep and cyclic large deformation cyclic tensile testing were used here to decouple elastic and viscous effects. A large variation in the recoverable shear strain (∼7.2% to ∼28%) was seen for glutens from 15 U.S. popular common wheat cultivars with varying HMW subunits. Sedimentation values ranged from 29 to 57 ml for 12 hard wheat cultivars and 15 to 22 ml for three soft wheat cultivars. The tensile force at 500% extension ranged from 0.12 to 0.67 N for hard wheat glutens and from 0.10 to 0.20 for soft wheat glutens. However, the recoverable work after large extension was less than 40% of the total work of extension. In addition, recoverable work in tensile testing was highly correlated with the total work of extension (r² = 0.97) and mixograph mix times (r² = 0.81). Good to excellent bread volume was obtained for several cultivars from this sample set. This suggests that optimizing water absorption for mixing doughs to achieve maximal bread volume compensates for the wide range of viscoelastic behaviors of gluten.     

Influence of sulphur fertilisation on quantities and proportions of gluten protein types in wheat flour

Although different supplies of sulphur (S) during wheat growth are known to influence the quantitative composition of gluten proteins in flour, an effect on the amount and on the proportions of single protein types has yet not been determined. Therefore, wholemeal flours of the spring wheat ‘Star’ grown on two different soils and at four different levels of S fertilisation (0, 40, 80, 160 mg S per container) were analysed in detail using an extraction/HPLC procedure. The results demonstrated that the amount of total gluten proteins as well as of the crude protein content of flour was little influenced, whereas amounts and proportions of single protein types were strongly affected by the different S fertilisation. The changes were clearly dependent on the Cys and Met content of each protein type. The amount of S-free ω-gliadins increased drastically, and that of S-poor high-molecular-weight (HMW) glutenin subunits increased moderately in the case of S deficiency. In contrast, the amounts of S-rich γ-gliadins and low-molecular-weight (LMW) glutenin subunits decreased significantly, whereas the amount of α-gliadins was reduced only slightly. S deficiency resulted in a remarkable shift of protein proportions. The gliadin/glutenin ratio increased distinctly; ω-gliadins became major components, and γ-gliadins minor components, whereas the ratio of HMW to LMW glutenin subunits was well-balanced.     

Effects of enzymatic hydrolysis on molecular structure and antioxidant activity of barley hordein

Hordein, the major storage protein of barley (Hordeum vulgare L.), was hydrolysed by three selected proteases, including alcalase, flavourzyme and pepsin. The effects of protease type and hydrolysis time on hordein molecular weight, surface hydrophobicity, secondary structure and antioxidant activity were investigated. Flavourzyme hydrolysis of hordein was relatively more extensive and rapid, resulting in the formation of medium- and small-sized peptides with a broad distribution within 30 min. Alcalase and pepsin more gradually and less extensively hydrolysed hordein into medium- and larger-sized peptides, respectively. Protein surface hydrophobicity decreased with an increasing degree of hydrolysis. The flavourzyme and alcalase hydrolysates had superior DPPH (1,1-diphenyl-2-picryl hydrazyl) free radical scavenging activity (44-70 and 48-58%, respectively, at 0.5 mg/mL), Fe²⁺-chelating ability (21-64% and 39-73%, respectively, at 1 mg/mL), and superoxide radical scavenging capacity. It is proposed that the large- and medium-size hydrolysate fractions were most likely responsible for the antioxidant activities of hordein hydrolysates, and could be used as antioxidant peptides in food and nutraceutical applications.     

Interaction of water unextractable solids and xylanase with gluten protein: effect of wheat cultivar

A previously proposed explanation for the change in gluten properties on addition of pentosans to doughs was based on data for only one wheat cultivar. Using three wheat cultivars, Scipion, Soissons and Amazon, differing in technological quality from weak to strong we have obtained results that support the previous explanation. In addition to standard techniques for characterizing gluten and glutenin macropolymer (GMP) yield, composition and properties, a new technique (particle size analysis) was applied that provides further detail on GMP particle size distribution. For each of the three wheat cultivars the effect of WUS and xylanase on gluten and GMP yield, composition and properties followed the trend previously observed. However, WUS and xylanase affected gluten yield and properties more strongly for Scipion and Soissons than for Amazon. Amazon flour contains more protein and less pentosans. The analysis of GMP particles demonstrates that the volume surface average particle diameter D_3,2 of GMP particles from Amazon wheat is larger than those from Scipion and Soissons. Amazon has the ability to form larger and stickier particles. These factors may explain why the effects of pentosans and xylanase on gluten yield and properties are smaller for this wheat.     

Effect of lipid incorporation on functional properties of wheat gluten based edible films

Wheat gluten is an inexpensive protein derived from mill industries with good film forming properties, which allows producing semipermeable membranes able to slow down water migration in foods.The first objective of this study was to evaluate the effects of the incorporation of a lipid phase (25 wt%, dry basis) in wheat gluten on the functional properties of the film, such water sorption, surface hydrophilicity, water barrier properties, mechanical properties and thermal properties. The second one was to asses if such incorporation was able to reduce the water sensitivity of film mechanical properties.Findings clearly showed that the incorporation of a lipid phase was able to decrease the water sorption, water affinity (hydrophilicity) and water transfer (≈2 times) of wheat gluten films. Moreover, mechanical properties are also affected by the lipid addition with a decrease in rigidity and, at high a_w, an increase in extensibility. However, the sensitivity of the mechanical properties to water was not modified. Lastly, DSC (Differential Scanning Calorimetry) analysis proved that changes in mechanical properties of films as a function of hydration state were the consequence of glass transition depletion, which allowed them to turn from a glassy-like behavior to a rubber-like behavior.     

大豆分离蛋白酶解产物功能特性的研究

研究了大豆分离蛋白的碱性蛋白酶和木瓜蛋白酶水解产物各种加工功能性质的变化趋势,并比较了两种酶在各个不同酶解时间下水解产物的各种功能性质。结果表明:大豆分离蛋白酶解产物比大豆分离蛋白的溶解性、乳化性、发泡能力和吸油性都有所改善;大豆分离蛋白木瓜蛋白酶水解产物保水性、乳化性、吸油性、发泡能力、粘度、凝胶性均优于大豆分离蛋白碱性蛋白酶水解产物。     

The effect of gluten on the retrogradation of wheat starch

The retrogradation of amylopectin in a wheat starch and a wheat starch/gluten (10:1) blend prepared by extrusion and containing 34% water (wet weight basis) was studied using X-ray diffraction, differential scanning calorimetry and NMR relaxometry during storage at constant water content and temperature (25 °C). For both samples, amylopectin ‘fully’ retrograded after 2–3 days storage, i.e. the different parameters monitored with time to follow the retrogradation had reached their maximum value, and crystallised predominantly into the A polymorph. Under the experimental conditions used, there was no evidence of any significant effects of the presence of gluten on the kinetics, extent or polymorphism of amylopectin retrogradation.     

Effects of washing, milling and loading enzymes on the enzymatic hydrolysis of a steam pretreated sugarcane bagasse

Enzymatic hydrolysis of steam pretreated sugarcane bagasse was performed to investigate the production of glucose and xylose. A blend of industrial enzymes (Novozymes) was used. The enzymes were used either without having been washed or having been washed with water or 1% aqueous NaOH solution. The influence of the size of sugarcane bagasse and the proportion of the enzymatic cocktail, which was composed of endoglucanases/cellobiohydrolases (Celluclast 1.5L) and β-glucosidase (Novozym 188) cellulases mixtures, was investigated. The tests were performed at a temperature of 50 °C and at a pH of 4.8 during a period of 72 h. The assays that were conducted with a pretreated sugarcane bagasse that was washed with a 1% aqueous NaOH solution without milling led to the largest amounts of glucose after 72 h, which was independent of the proportions of enzymes used in experiments with the smallest amounts of enzymes. The largest amount of xylose was obtained with a pretreated sugarcane bagasse that was not washed.     

Effect of hydrostatic pressure and temperature on the chemical and functional properties of wheat gluten: Studies on gluten, gliadin and glutenin

The effect of hydrostatic pressure (0.1–800 MPa) in combination with various temperatures (30–80 °C) on the chemical and physical properties of wheat gluten, gliadin and glutenin was studied. Chemical changes of proteins were determined by extraction, reversed-phase high-performance liquid chromatography (HPLC), sodium dodecylsulphate (SDS) polyacrylamide gel electrophoresis (PAGE), circular dichroism (CD) spectroscopy, thiol measurement and studies on disulphide bonds. Rheological changes were measured by extension tests and dynamic stress rheometry. Treatment of gluten with low pressure (200 MPa) and temperature (30 °C) increased the proportion of the ethanol-soluble fraction (ESF) and decreased gluten strength. The enhancement of both pressure and temperature provoked a strong reduction of the ESF and the thiol content of gluten. Within gliadin types, cysteine containing α- and γ-gliadins, but not cysteine-free ω-gliadins were sensitive to pressure and were transferred to the ethanol-insoluble fraction. Disulphide peptides isolated from treated gluten confirmed that cleavage and rearrangement of disulphide bonds were involved in pressure-induced reactions. Increased pressure and temperature induced a significant strengthening of gluten, and under extreme conditions (e.g. 800 MPa, 60 °C), gluten cohesivity was lost. Isolated gliadin and glutenin reacted differently: solubility, HPLC and SDS-PAGE patterns of gliadin having a very low thiol content were not influenced by pressure and heat treatment; only conformational changes were detected by CD spectroscopy. In contrast, the properties of isolated glutenin having a relatively high thiol content were strongly affected by high pressure and temperature, similar to the effects on total gluten.     

Effect of temperature variation during grain filling on wheat gluten resistance

The objective was to investigate effects of natural variation in temperature during grain filling on wheat (Triticum aestivum L) gluten quality. Seventeen field trials with four different varieties were conducted during the years 2005–2008. Temperature records were obtained from automatic weather stations located near the field trial sites. The period from heading to yellow ripeness was divided into 20 sub-phases of equal thermal time units, and a last sub-phase comprising the seven days after yellow ripeness. Partial Least Squares Regression was used to relate the temperature records of the different sub-phases to gluten quality analysed by the Kieffer Extensibility test and the SDS sedimentation test.     

Enriching novel Glu-Ax alleles and significantly strengthening gluten properties of common wheat through wide hybridization with wild emmer

Two hybrids, BAd7-209 and BAd7-210, were obtained by wide hybridization between wild emmer D97 and weak gluten cultivar CN16. They had a genetic background of common wheat, resulting from continuous selfing over nine times. These hybrids were better than CN16 in dough quality and processing quality tests. BAd7-210 was better than medium gluten wheat cultivar MM37, and BAd7-209 was far better than moderate to strong gluten wheat cultivar SM482. Through chromosome engineering, BAd7-210 possessed the 1Ax2.2 of male D97, and BAd7-209 had the 1Ax1.2 which was caused by complex variation because of cross-parents’ genomic asymmetry. The open reading frames (ORFs) of two novel active Glu-Ax alleles 1Ax2.2 and 1Ax1.2 were 2496 bp and 2514 bp, encoding 830 and 836 amino acid residues, respectively. The 1Ax1.2 was the second longest Glu-Ax gene discovered to date, and it had two deletions and one insertion besides many single nucleotide polymorphisms (SNPs) compared with the 1Ax2.2 and 1Ax1. The longer polypeptide of 1Ax1.2 should explain why BAd7-209 has better processing quality than BAd7-210. Therefore, wild emmer could be effectively utilized to enrich the 1Ax alleles of common wheat through direct cross transferring and generating novel allele variation, which could significantly enhance the gluten strength.     

Introgression of transgenes into a commercial cultivar confirms differential effects of HMW subunits 1Ax1 and 1Dx5 on gluten properties

Transgenes encoding the HMW subunits 1Ax1 and 1Dx5 have been transferred from “model” wheat lines into the commercial French bread wheat cultivar Soissons, using three backcrosses. Five pairs of BC3 expressing and null lines were isolated from each cross and multiplied to provide grain for functionality studies. Analysis of white flour samples confirmed the expression of the transgenes. SE-HPLC and Reomixer studies showed that the two transgenes had differential effects on dough functional properties. Thus, subunit 1Dx5 resulted in detrimental effects on dough development which were associated with decreased extractability of large glutenin polymers. In contrast, lines expressing subunit 1Ax1 contained increased proportions of extractable large glutenin polymers with three lines showing higher torque at similar mixing times (i.e. increased dough strength). This confirms the results obtained with the model wheat lines and shows that the 1Ax1 transgene can be used to increase dough strength in commercial cultivars.     

Improving effect of lyophilization on functional properties of resistant starch preparations formed by acid hydrolysis and heat treatment

In this study, effects of lyophilization on the functional properties of acid modified and autoclaved corn starch preparations were investigated. RS contents and pasting properties of these starch preparations were also determined. Significant increases in solubility were observed as the hydrolysis level of the lyophilized samples increased. All of the acid-modified gelatinized–autoclaved–lyophilized samples had higher water binding values than those of native starch and heat treated oven-dried native starch. Acid-modified gelatinized–autoclaved–lyophilized samples (with storage at 95°C: GASL or without storage: GAL, before lyophilization) improved emulsion properties of soy protein solution significantly. Acid modification seems to be a prerequisite to achieve improving effect of lyophilization. While native starch did not contain any RS, the level increased to 8.1% due to gelatinization, autoclaving and oven-drying (Control 2). The RS content of Control 2 was higher than that of gelatinized–autoclaved–lyophilized native starch (N-GAL, 2.9%). The samples stored prior to lyophilization had higher RS contents as compared to the corresponding unstored samples. The highest RS content (12.4%) was observed in 2h-GASL sample. Cold viscosity was observed in the RVA curves of N-GASL, 2h-GASL, N-GAL and 2h-GAL samples. A possible mechanism/model is suggested to explain the lack or existence of a cold viscosity.     

Variation in rheological properties of gluten from three biscuit wheat cultivars in relation to nitrogen fertilisation

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.