玉米淀粉生物降解地膜的研究

以玉米淀粉(ST)及聚乙烯醇(PVA)为原料,制备全生物降解地膜。研究了ST-PVA交联反应的最适条件及增塑剂的最佳用量,并初步探讨了纳米SiO2对膜拉伸强度的影响,结果表明:复合交联剂甲醛与多聚磷酸钠(二者用量比1∶2)的最适用量为3%;交联反应的最适时间20min、温度为90℃、搅拌速度为120r·min-1;加入3.3%的MgCl2有利于交联反应;复合增塑剂甘油与乙二醇(二者比例为1∶3)的最佳用量为3.2%;添加0.03%的纳米SiO2对膜的拉伸强度有显著的提高。     

Microbial transglutaminases generate T cell stimulatory epitopes involved in celiac disease

Celiac disease (CD) is a permanent intolerance to gluten. In CD patients, gluten peptides cause an inflammation in the small intestine leading to tissue damage. Tissue transglutaminase (tTG) is an enzyme involved in the repair of damaged tissue by crosslinking of extracellular matrix proteins. Under certain conditions, tTG can deamidate glutamine into glutamic acid. Compared to native gluten, deamidated gluten elicits a more powerful inflammatory response. To improve the quality and texture of food products microbial transglutaminases (mTG) are used in the food industry.     

Immunomodulatory activities of non-prolamin proteins in wheat germ and gluten

Albumin (Alb), globulin (Glo), glutelin (Gll) and glutenin (Gln) were separately extracted from wheat germ and wheat gluten. Amino acisd composition, molecular weight distribution, solubility, in vitro digestibility, and immunomodulatory activities were all analyzed. Gll and Gln have similar molecular weight distributions, which differed from those of Alb and Glo. Alb showed the highest solubility at various pH values (except pH 4.0), whereas Glo showed the highest in vitro digestibility. Glo and Gll have the highest proportion of essential to total amino acids, while Alb and Gll have the highest protein digestibility-corrected amino acid scores. Gll had the strongest immunomodulatory effects in terms of stimulation of RAW 264.7 cells to produce IL-6, TNF-α, and IL-10, and good stimulatory effects on splenocyte proliferation, production of IL-2, phagocytosis, and secretion of nitric oxide in RAW 264.7 cells. Gll can be considered a good protein source for use in health foods.     

Use of chemical redox agents and exogenous enzymes to modify the protein network during breadmaking – A review

During breadmaking, a continuous protein network is formed which confers visco-elasticity to dough. The properties of this protein network are highly dependent on the characteristics of the gluten proteins of the wheat flour. A good quality (highly elastic) gluten network retains the carbon dioxide that is produced by the yeast, giving dough and bread with optimal properties. However, the properties of the gluten proteins can differ substantially between wheat flours and are highly dependent on genetic, environmental and post-harvest conditions. Deficiencies in wheat quality for breadmaking can be overcome by incorporating exogenous components which alter the functionality of the gluten proteins during breadmaking. These include additives (e.g. potassium bromate, iodate, chlorine dioxide and chlorine, azodicarbonamide, ascorbic acid and peroxides) and enzymes affecting protein crosslinking. Transglutaminase, glucose oxidase, hexose oxidase and laccase all promote the formation of covalent bonds between gluten proteins and, hence, can serve as alternatives to chemical bread improvers.     

Relationships between dough strength,polymeric protein quantity and composition for diverse durum wheat genotypes

Five different Glu-B1 HMW-GS patterns were identified among a collection of diverse durum wheat genotypes grown in 2001 in two locations in western Canada. The durum wheat lines exhibited a wide range of dough and gluten strength characteristics as measured by alveograph and 2 g mixograph parameters, gluten index (GI), and protein composition as measured by unextractable polymeric protein (UPP) content and the ratio of high-molecular weight (HMW) glutenin subunits (GS) to low-molecular weight (LMW) GS. HMW-GS subunits patterns represented within the genotypes were 6+8, 7+8, 7+16, 14+15 and 20. Two of the genotypes expressed Glu-A1 HMW-GS 2* in combination with other HMW-GS. Approximately 95% of the durum genotypes were γ-gliadin 45 types. Analysis of variance indicated that genotype was a greater source of variation in all measurements than was growing location, with the exception of protein content which showed less variation contributed by genotype and more contributed by location than for other quality parameters. UPP was strongly associated with all strength measurements. All of the γ-gliadin 42 types were low in UPP and weak. Among the γ-gliadin 45 types, those possessing HMW-GS 20 were typically in the lower half of the UPP and strength range. There was no clear evidence of an association between any of the other HMW-GS patterns and gluten strength. The majority exhibited HMW to LMW-GS ratios that were within the relatively narrow range of 0.15–0.25, yet there were wide variations in dough strength among genotypes within that range. Increasing proportions of HMW-GS resulting in ratios of greater than 0.30 were generally associated with weak dough and gluten and low UPP content.     

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.     

Impact of different isolation procedures on the functionality of zein and kafirin

Commercial corn prolamin (zein) aggregates in water at elevated temperatures into an extensible, viscoelastic gluten-like substance. This specific functionality of zein can be used in the production of gluten-free bread from true dough systems and not from batters. The present study examined laboratory-scale isolation of such functional zein from dry milled corn. RP-HPLC indicated that successful isolation procedures resulted in relatively pure α-zeins, with a maximum ratio of (β + γ)/α-zeins of about 10%. In the present study, such functional zeins were obtained by using 70% ethanol as the extractant, without added alkali or reducing agent in the main extraction step. In contrast, films could be cast from a wider range of zein isolates, also with higher ratios of (β + γ)/α-zeins. Isolation of the analogous prolamin (kafirin) from dry milled sorghum required a more hydrophobic extractant such as 83% isopropanol to achieve partial functionality. Such kafirin was able to aggregate in warm water, preferably when a reducing agent was added; however, it quickly became firm and lost its extensibility. The present study suggests that hydrophobic interactions rather than disulfide bonds are the key to gluten-like functionality of zein and kafirin.     

新疆小麦1BL/1RS易位和 Dx5基因的多重PCR检测及其面筋品质分析

为了给新疆小麦面筋品质改良提供参考依据,利用多重PCR体系对267份新疆冬、春小麦品种中1BL/1RS易位和 Dx5基因的分布进行了检测,并测定了其中181份小麦品种的面粉蛋白质含量、湿面筋含量、Zeleny沉淀值以及面团特性等品质性状。结果表明,新疆小麦品种中,1BL/1RS易位品种有55份,占20.6%,含有 Dx5基因的品种有76份,占28.5%。冬小麦品种中1BL/1RS易位系分布频率（26.6%）显著高于春小麦（9.6%）,而春小麦品种中 Dx5基因的分布频率（31.9%）高于冬小麦（26.6%）。在新疆小麦农家品种、引进品种和自育成品种中,1BL/1RS易位和 Dx5基因的分布频率也存在明显差异。分析表明,1BL/1RS和非1BL/1RS小麦品种的主要面筋品质性状（如Zeleny沉淀值、峰值高度、8 min宽度等）达到显著性差异（P＜0.05）,1BL/1RS小麦中含 Dx5和不含 Dx5基因品种的面筋指数、Zeleny沉淀值、峰值时间和8 min面积等5个参数差异达到显著水平（P＜0.05）。多重PCR体系检测结果可靠稳定,节省实验经费和时间,提高了效率,可用于小麦分子辅助育种。     

Deamidation of gluten proteins and peptides decreases the antibody affinity in gluten analysis assays

Wheat gluten is a widely used ingredient in the food industry due to its unique properties and relatively low price. Modification of wheat gluten makes it a versatile ingredient and, thus, increases its applicability in foods. Therefore, gluten proteins can be found in unexpected sources, and this makes the gluten-free diet challenging to follow. Deamidation is one way to modify protein structure. It increases solubility and surface activity of gluten improving its functionality, but consequently, also influencing the accuracy of quantification by immunoassays. In this study, the effect of deamidation on the antibody recognition with gluten analysis methods based on monoclonal R5, omega-gliadin or G12 antibodies was studied. Random deamidation decreased the intensities to 13–54% of the intensity obtained for the intact peptides. Deamidation representing the transglutaminase deamidation decreased the intensities to 4–8%. Deamidation of gluten proteins abolished the recognition by omega-gliadin and G12 antibodies and decreased the recognition of R5 by 600 times when analyzed by the sandwich method and 125 times by the competitive method. In conclusion, with all of the investigated gluten-specific antibodies, deamidation decreased the affinity of antibodies to gluten peptides and proteins, which needs to be considered when assays and regulations are developed for gluten-free products.     

Molecular mapping of QTLs for gluten strength as measured by sedimentation volume and mixograph in durum wheat (Triticum turgidum L. ssp durum)

Quantitative trait loci (QTLs) responsible for gluten strength measured by SDS-sedimentation volume (SV), mixograph and grain protein content (GPC) were located on the molecular linkage map of a durum wheat recombinant inbred line population. QSv.macs-1B.1 flanked by Xgwm550–Glu-B3 was the most consistent QTL for SV identified in all the environments. The same QTL was also associated with mixograph peak energy, peak time and total energy. The Glu-B1 locus was at the center of another QTL responsible for SV, while, Glu-B2 influenced SV as well as mixograph peak energy and peak time. Apart from glutenin coding loci, QTLs influencing mixing parameters and GPC were located in three other marker intervals Xwmc48.2–Xpsp3030 (4B), Xgwm573–Xbarc231.1 (7A) and Xgwm46–Xgwm540.1 (7B). A total of 26 main effect QTLs and 10 digenic epistatic interactions (QQ) for quality traits were distributed over 11 chromosomes. Out of these, seven main effect QTLs and three QQ interactions were involved in interactions with environments (QE, QQE). The results indicated that along with chromosome 1B, chromosomes 4B, 7A and 7B are also important for improvement of gluten strength and GPC in durum wheat.