Effects of enzymatic deamidation by protein-glutaminase on structure and functional properties of alpha-zein

The performance of novel protein-glutaminase (PG) purified from Chryseobacterium proteolyticumon alpha-zein was investigated. Highly insoluble alpha-zein was able to be deamidated to the extent of deamidation degree 62% by using 50 mM potassium phosphate (pH 8) containing 11.7% ethanol, at 40 degrees C for 137 h. Analysis by sodium dodecyl sulfate polyacrylamide-gel electrophoresis showed that deamidated and non-deamidated zeins have different mobilities. Results of circular dichroism spectra revealed the decline in alpha-helix contents of alpha-zein by deamidation. Besides, Fourier transform infrared spectroscopy analysis demonstrated alterations in the secondary structure of alpha-zein by deamidation. The assignment of the amide I region showed a remarkable decrease in antiparallel intermolecular beta-sheets (around 1690 cm(-1)) as an indication of the weakening aggregation ability of the deamidated molecules. Solubility and emulsification properties of alpha-zein, particularly at pH 7, were remarkably improved after the deamidation by PG. Gas chromatography and peroxide value studies pointed out that deamidated alpha-zein in powder form exhibited an inferior antioxidative property as compared with the non-deamidated one.     

Optimization of the enzymatic deamidation of soy protein by protein-glutaminase and its effect on the functional properties of the protein

The effects of enzymatic deamidation by protein-glutaminase (PG) on the functional properties of soy protein isolate (SPI) were studied. Conditions for the deamidation were evaluated by means of response surface methodology (RSM). Optimal conditions based on achieving a high degree of deamidation (DD) with a concurrently low degree of hydrolysis (DH) were 44 °C, enzyme:substrate ratio (E/S) of 40 U/g protein and pH 7.0. Under optimal conditions, both DD and DH increased over time. SDS-PAGE results indicated that lower molecular mass subunits were produced with increasing DD. Far-UV circular dichroism spectra revealed that the α-helix structure decreased with higher DD, while the β-sheet structure increased until 15 min of deamidation (32.9% DD), but then decreased at higher DD. The solubility of deamidated SPI was enhanced under both acidic and neutral conditions. SPI with higher DD showed better emulsifying properties and greater foaming capacity than SPI, while foaming stability was decreased. It is possible to modify and potentially improve the functional properties of SPI by enzymatic deamidation using PG.     

Effects of solid-state enzymatic treatments on the antioxidant properties of wheat bran

This study evaluated the potential of solid-state enzyme treatments to release insoluble bound antioxidants such as phenolic acids from wheat bran, thereby improving its extractable and potentially bioaccessible antioxidant properties including scavenging capacities against peroxyl (ORAC), ABTS cation, DPPH and hydroxyl radicals, total phenolic contents, and phenolic acid compositions. Investigated enzyme preparations included Viscozyme L, Pectinex 3XL, Ultraflo L, Flavourzyme 500L, Celluclast 1.5L, and porcine liver esterase. Results showed significant dose-dependent increases in extractable antioxidant properties for some enzyme preparations, and Ultraflo L was found to be the most efficient enzyme, able to convert as much as 50% of the insoluble bound ferulic acid in wheat bran to the soluble free form. The effect of moisture content on these solid-state enzyme reactions was also evaluated and found to be dependent on enzyme concentration. These data suggest that solid-state enzyme treatments of wheat bran may be a commercially viable post-harvest procedure for improving the bioaccessibility of wheat antioxidants.     

Analysis of taste-active compounds in an enzymatic hydrolysate of deamidated wheat gluten

Hydrolyzed plant proteins are widely used as ingredients in culinary products for their glutamate-like ("umami") taste. Three hydrolysates were prepared from wheat gluten using different enzymatic approaches. Comparison of their taste profiles revealed the enzymatic hydrolysate of an acid-deamidated wheat gluten (WGH-3) to be the least bitter of all and to elicit an intense glutamate-like taste. Its umami taste intensity was similar to that of an enzymatic hydrolysate in which glutaminase had been employed to convert free glutamine to glutamic acid and which had a 3-fold higher concentration of free glutamate. Reconstitution studies based on the results of the chemical analysis of WGH-3 and sensory comparison of the model solution and WGH-3 indicated that other components in addition to glutamate and organic acids contribute to its glutamate-like taste. WGH-3 was fractionated by gel permeation chromatography and reversed phase high-performance liquid chromatography, and two fractions with a pronounced glutamate-like taste were obtained. In one of them four pyroglutamyl peptides were tentatively identified: pGlu-Pro-Ser, pGlu-Pro, pGlu-Pro-Glu, and pGlu-Pro-Gln. Apparently, these peptides were formed by cyclization of the N-terminal glutamine residues during the preparation of the hydrolysates.     

Drying temperature and relative humidity effects on wheat gluten film properties

The mechanical and physical properties of glycerol-plasticized wheat gluten films dried at different temperatures (20, 50, and 80 degrees C) and relative humidities (35 and 70% RH) were investigated. Dispersion of wheat gluten was prepared at pH 11 in aqueous solution. Films were obtained by casting the wheat gluten suspension, followed by solvent evaporation in a temperature and relative humidity controlled chamber. Decreasing relative humidity altered most of the mechanical properties. At 35% RH, tensile strength increased when drying temperature increased. However, at 70% RH, tensile strength decreased when temperature increased. Thickness of the films decreased by increasing temperature. Hypothetical coating strength increased with increasing drying temperature at 35% RH. However, at 70% RH, a maximum value was observed at 50 degrees C. Films produced at 80 degrees C exhibited low solubility in aqueous solution. Addition of 1.5% (w/v) sodium dodecyl sulfate increased solubility of all of the films except the film dried at 50 degrees C and 70% RH. Overall, drying temperature and relative humidity affected mechanical and physical properties of the wheat gluten films. However, the effect of drying temperature was more pronounced than the effect of relative humidity.     

燕麦麸分离蛋白的酶解对其功能性质的影响

为了改善燕麦蛋白的功能性质以扩大其在食品工业中的应用,该文以燕麦麸为原料制备了燕麦麸分离蛋白(OBPI),并利用胰蛋白酶对其进行水解,得到了3种不同水解度(4.1%、6.4%、8.3%)的酶解产物。SDS-PAGE分析结果表明OBPI中的主要蛋白成分是球蛋白,其经过胰蛋白酶处理后,球蛋白酸性亚基被部分水解而碱性亚基相对保持完整。胰蛋白酶水解显著改变了OBPI的功能性质。在所考察的水解度范围内,随着水解度的升高,酶解产物的溶解性、持水性、乳化活性及起泡能力等方面均逐渐增加;但持油性、乳化及泡沫稳定性有不同程度的降低。     

Impact of protein size distribution on gluten thermal reactivity and functional properties

Wheat gluten structure was modified in different ways: Disulfide bonds were reduced by sulfitolysis, or protein chains were enzymatically hydrolyzed at three different degrees of proteolysis. A kinetic study of the thermal reactivity of the modified glutens showed that gluten aggregation kinetic was slowed in consequence to the shift of gluten size distribution toward smaller proteins. In contrary to sulfitolysis, proteolysis also affected the gluten reactivity potential because of the formation of numerous nonreactive species. Moreover, the thermally induced browning reaction was greatly enhanced by proteolysis, which increased the amount of free amine residues, substrates of the Maillard reaction. On the contrary, a whitening effect was observed for reduced gluten with bisulfite. Proteolysis was also found to decrease plasticized gluten viscosity, to increase gluten-based materials water solubility, and to enhance gluten adhesiveness properties but to reduce its mechanical performance. Sulfitolysis was considered as a possible way of extending gluten processability by extrusion or injection molding, whereas proteolysis was found to confer enhanced gluten stickiness that suggests new potential end uses of gluten in the pressure sensitive adhesives domain.     

Isolation and identification of indigestible pyroglutamyl peptides in an enzymatic hydrolysate of wheat gluten prepared on an industrial scale

An enzymatic hydrolysate of wheat gluten was further digested in vitro with porcine pepsin and pancreatin to obtain an indigestible peptide. Indigestible pyroglutamyl peptide was isolated from the digest by strong cation-exchange, size-exclusion, and reversed-phase chromatographies. The pyroglutamyl peptide was digested with pyroglutamate aminopeptidase, and the digest was reacted with phenyl isothiocyanate. The resultant phenylthiocarbamyl (PTC) peptides were purified by reversed-phase HPLC by using binary gradient elution with ammonium acetate buffer, pH 6.0, and acetonitrile. The PTC peptides were analyzed with an automatic peptide sequencer on the basis of the Edman degradation method with a modified program. Some pyroglutamyl peptides were also analyzed by fast-atom bombardment ionization mass spectrometry without the pyroglutamate amino peptidase digestion. Consequently, pyroGlu-Asn-Pro-Gln, pyroGlu-Gln-Gln-Pro-Gln, pyroGlu-Gln-Pro-Gln, pyroGlu-Gln-Pro-Gly-Gln-Gly-Gln, pyroGlu-Gln, pyroGlu-Gln-Pro, pyroGlu-Ile-Pro-Gln, pyroGlu-Ile-Pro, pyroGlu-Gln-Pro-Leu, pyroGlu-Gln-Phe-Pro-Gln, pyroGlu-Ser-Phe-Pro-Gln, pyroGlu-Phe-Pro-Gln, and pyroGlu-Gln-Pro-Pro-Phe-Ser were identified.     

槲皮素对挤压大米淀粉结构及功能特性的影响

为改善挤压大米淀粉的功能特性,以米粉（rice, R）为主要原料,探究了不同槲皮素（quercetin, Q）添加量（0 ～ 10%）在挤压场下对米粉中淀粉的水溶性、吸水性、糊化特性等功能特性的影响。在此基础上,借助扫描电子显微镜（scanning electron microscopy）、X-射线衍射、红外光谱、及紫外可见光分光光度计揭示了Q在挤压场下对淀粉结构的演变规律。试验结果表明：当Q添加量为4%时,样品的吸水指数,碘结合能力均达到了最大值,且自由水弛豫时间提前;挤压体系中Q与淀粉通过氢键结合,颗粒结构变得更加立体、紧凑。与挤压米粉相比,槲皮素的添加延缓了淀粉的回生且提高了淀粉的热稳定性。根据以上结果可知,挤压体系中Q与大米淀粉复合,促进了淀粉分子链重排,进而改变淀粉的结构及功能特性,该研究可为开发抗回生的挤压大米淀粉基产品提供理论依据。     

等离子体处理对亚麻籽胶结构和功能特性的影响

为了揭示等离子体技术对亚麻籽胶的物理改性效应,该研究以5 mg/mL亚麻籽胶溶液为对象,比较了不同等离子体处理时间(0～120 s)对亚麻籽胶结构和功能特性的影响规律.结果发现,随着等离子体处理时间的延长,亚麻籽胶溶液pH值、Zeta电位绝对值和平均分子量逐渐减小,而对亚麻籽胶的多糖骨架结构和单糖组成无明显影响.等离子...     

施氮量对强筋和中筋小麦产量和品质及养分吸收的影响

以强筋小麦皖麦38和中筋小麦皖麦44为材料,研究了施氮量对子粒产量、品质及植株养分吸收的影响,分析了植株体内N、P、K素含量与子粒品质性状的相关性。结果表明,施氮量在0-300kg／hm2范围内,氮素与两种类型小麦的子粒产量和蛋白质产量均呈二次曲线关系,增施氮素不仅能显著提高蛋白质、湿面筋含量和沉降值,降低弱化度,延长面团的形成时间和稳定时间,有利于植株对氮的吸收,而且还能提高P、K的营养水平。植株体内N的含量除与吸水率和弱化度相关不显著外与其它主要品质性状的相关系数都达到极显著水平,只有容重为负相关;皖麦38和皖麦44达到最高子粒产量的施氮量分别为224.6.kg／hm2和207.5.kg／hm2,达到最高蛋白质产量的施氮量分别为288.5.kg／hm2和221.0.kg／hm2。     

氮磷互作对弱筋小麦氮素利用与籽粒淀粉品质的影响

为了解氮磷对弱筋小麦品种氮素利用效率及籽粒淀粉品质的影响,以宁麦13为材料,在施氮120kg/hm2(N1)、180 kg/hm2(N2)水平下,分别设置3个磷素水平(施P2O5水平为P1:60 kg/hm2,P2:120 kg/hm2,P3:180 kg/hm2),分析氮磷素对弱筋小麦植株氮素吸收利用、籽粒淀粉粒度分...     

挤压稳定化处理对米糠各组分蛋白结构及功能性质的影响

为了研究挤压稳定化处理对米糠各组分蛋白结构和功能性质的影响,选取龙粳31号大米米糠做为原料,采用双螺杆挤压技术对该原料进行稳定化处理。结果表明：米糠各组分蛋白在挤压处理后溶解性、起泡性和持油性显著降低（P?0.05）,持水性、起泡稳定性和乳化稳定性升高,谷蛋白持水性提高的幅度最大,较挤压前提高了39%。米糠谷蛋白的乳化活性与其他两种组分蛋白差异显著,清蛋白和球蛋白较挤压前分别降低5%和10%,谷蛋白乳化活性增加,较挤压前增加8%。结构特性分析结果表明产生这种差异的主要原因不是分子间作用力,而是挤压后各组分蛋白发生重组,形成大的聚集体过程中二级结构的变化截然相反,米糠清蛋白α-螺旋、β-转角和无规则卷曲含量都有所降低,β-折叠含量增势明显提高。挤压后的米糠谷蛋白结构与白蛋白显示出不同的趋势,谷蛋白的二级结构在酰胺I带变化显著,α-螺旋、β-转角与无规则卷曲的含量有所提高,β-折叠的含量下降。结果可为米糠各组分蛋白的工业化制备及在各种食品配方中的应用提供理论支撑。     

Influence of gallic acid and tannic acid on the mechanical and barrier properties of wheat gluten films

Vital wheat gluten, a byproduct of wheat starch production, is a highly functional ingredient having a unique viscoelasticity that makes it ideal for the production of edible biodegradable films. However, its functional properties must be modified to ensure sufficient strength and elasticity, in addition to water vapor barrier properties. In this study, vital gluten was modified using tannic and gallic acid. It was found that the addition of tannic acid resulted in stiffer, more resistant, and less resilient and flexible films, having as well decreased water vapor permeability. Tannic acid containing films became reddish brown, whereas gallic acid addition did not have an influence on the film appearance. Films containing gallic acid became more elastic. Gallic acid was found to potentially act like a plasticizer. Scanning electron microscopy was used to investigate the ultrastructure of the produced films.     

氮素形态对强筋和中筋小麦产量和品质的影响

[目的]研究不同氮素形态对强筋和中筋小麦植株生长、籽粒蛋白质含量及产量的影响,为选择适宜氮肥种类、提高氮素利用率提供科学依据.[方法]选用强筋小麦'藁优2018'和中筋小麦'济麦22'在河北邢台进行田间试验.在相同施氮量下,设置5个氮源处理:不施氮肥(CK)、酰胺态氮肥(Urea)、铵态氮肥(NH4+-N)、硝态氮肥(...     

Some nutritional and functional properties of defatted wheat germ protein

Defatted wheat germ protein (DWGP) was isolated by alkaline extraction at pH 9.5 and subsequent isoelectric precipitation at pH 4.0, and its nutritional and functional properties were studied. The results showed that the amino acid content of defatted wheat germ was as high as 26.793 g/100 g, and the contents of eight essential amino acids were all relatively high. The isoelectric point of DWGP was 4.0. When pH >6.0, the DWGP had high solubility with a nitrogen solubility index of 70%. The emulsifying activity and emulsifying stability of DWGP were similar to those of bovine serum albumin and a little higher than those of casein. DWGP had good foaming capacity, but its foaming stability (FS) was not very good. However, the FS of DWGP can be improved through physical, chemical, or enzymatic methods. Moreover, DWGP had excellent water retention (WR); especially at pH 8.0 and a temperature of 70 degrees C, the WR of DWGP was the highest at 229.4%. DWGP offers is a potential source of functional protein isolate for possible food applications.     

Molecular determinants of the influence of hydrophilic plasticizers on the mechanical properties of cast wheat gluten films

The influence of a set of hydrophilic plasticizers varying in their chain length (ethyleneglycol and longer molecules) on the tensile strength and elongation at break of cast gluten films was studied. When considered on a molar basis (moles of plasticizer per mole of amino acid), the effect of the different plasticizers depended on their respective molecular weights for plasticizer/amino acid ratios in the range from 0.10 to 0.40. However, above a ratio of 0.40-0.50 mol/mol of amino acid, these differences were abolished and both stress and strain reached a plateau value, with all plasticizers studied. In fact, when a homologous series of molecules was considered, the ability for plasticizer to decrease stress and increase strain was closely related to the number of hydrogen bonds the molecule was able to share with the protein network. Ethyleneglycol's efficiency was, however, lower than expected from its hydrogen-bonding potential; a comparison with other diols demonstrated that this was due to the small size of this molecule. The particular effect of glycerol concentration on the films' mechanical properties suggested that other molecular features of the plasticizer, such as the number and position of hydroxide groups in the molecule, were involved in the plasticization mechanism.     

Study of the temperature effect on the formation of wheat gluten network: influence on mechanical properties and protein solubility

Modifications of mechanical properties of wheat dough during thermal treatments depend mainly on the capacity of wheat gluten proteins to establish intra- and intermolecular interactions when subjected to high-temperature processing. The present study investigates the effect of thermal treatments on the mechanical properties and protein solubility of wheat gluten-based network. The increase in treatment temperatures (from 80 to 135 C) induces an increase in mechanical resistance of the gluten network (tensile strength increases from 0.26 to 2.04 MPa) and a decrease in deformability (elongation decreases from 468 to 236%). The increase in temperature (from 80 to 135 C) also induces a very strong reduction of protein solubility in 2% SDS (from 68 to 0%) that could be correlated to the mechanical changes observed. It was concluded that the modifications of the wheat gluten network properties seem to depend mainly on the temperature level, as temperatures >108-116 C allow activation of thermosetting reactions.     

Effect of alkaline deamidation on the structure, surface hydrophobicity, and emulsifying properties of the Z19 alpha-zein

Different deamidation conditions for the Z19 alpha-zein were studied in order to find the best conditions for the development of the emulsifying properties. Alkaline deamidation was chosen, and the effects on the peptide bond cleavage, secondary structure, emulsifying properties, and surface hydrophobicity were studied. The Z19 alpha-zein was deamidated by using 0.5 N NaOH containing 70% ethanol at 70 degrees C for 12 h. A deamidation degree (DD) of 60.6 +/- 0.5%, and a degree of hydrolysis (DH) of 5 +/- 0.5% were achieved. Analysis by far-UV circular dichroism showed that the denaturation was mainly promoted by the high temperature used during the incubation. The adequate balance between the DD and the DH results in an effective emulsifying property improvement for the Z19 alpha-zein. Thus, after the deamidation treatment, the surface hydrophobicity decreased from 9.5 x 104 +/- 6.8 x 103 to 46 x 104 +/- 2.1 x 103, and the emulsion stability increased from 18 +/- 0.7% to 80 +/- 4.7% since the oil globules stabilized by the modified protein were smaller (57.7 +/- 5.73 nm) and more resistant to coalescence than those present in the native protein emulsions (1488 +/- 3.92 nm).