【作者】 王金水；

【导师】 赵谋明；

【作者基本信息】 华南理工大学 ， 食品科学， 2007， 博士

【摘要】 面筋蛋白是小麦淀粉生产过程中的副产品,由于在水中溶解性差,限制了在食品中的应用,本文旨在通过酶解-膜超滤改性,改善面筋蛋白功能特性以拓宽其应用范围。研究面筋蛋白酶解优化条件及内在规律,探讨酶解产物对酶解过程的抑制作用及机理,对改性面筋蛋白功能特性变化进行研究,通过超声辐射研究酶解面筋蛋白-多糖之间接枝反应,深入探讨了改性面筋蛋白组成、结构与功能特性之间的关系。选用Protamex、PTN 6.0S、Alcalase、Neutrase、Papain酶解面筋蛋白,优化酶解条件。酶解产物中可溶性氮、氨基氮、肽基氮含量变化表明,Protamex最适合产生不同分子量的肽,Papain次之,Neutrase最低;SDS-PAGE和SE-HPLC分析表明:酶解过程中,醇溶蛋白和可溶性麦谷蛋白易于降解,部分高分子麦谷蛋白亚基对酶解表现出“抗性”。加热、超声、挤压和还原剂等预处理改变了面筋蛋白的结构(SH/S-S、亲水性/疏水性等),使其酶解过程中DH和蛋白回收率增加,酶解前预处理对改善面筋蛋白酶解特性有明显的促进作用。酶解产物对酶解抑制率(IR)与DH之间的关系曲线表现出明显不同的两个动力学区域:DH依赖区和DH非依赖区;酶解产物中分子质量<5kDa的肽组分对酶解起主要的抑制作用,酶解-膜分离耦联可以明显改善面筋蛋白的酶解特性,酶活力下降速度减缓。利用不同截留分子量的膜超滤分离酶解产物得到改性面筋蛋白组分(50-K、30-K、10-K和P组分), SDS-PAGE和红外光谱分析表明不同面筋蛋白组分组成及结构有明显的差异。酶解产物溶解性、乳化性、起泡性、持水能力等较对照显著改善(P<0.05),但与DH有密切的关系,酶解产物黏度变化与其浓度和DH有关。改性面筋蛋白组分溶解性在pH3-10特别是在pH7.0时比对照显著提高(P<0.05),pI向碱性或酸性方向偏移,热(50-90°C)稳定性明显提高,低浓度KCl/Cys对改性面筋蛋白有增溶作用;乳化、起泡和持水能力显著(P<0.05)改善,30-K组分增加最大,改性后乳化稳定性和泡沫稳定性降低;改性面筋蛋白黏度下降,但随浓度升高而增加;表面疏水性增加且随肽段分子量降低而下降;初始化成胶温度升高但随离子强度增加而降低,50-K组分凝胶具有相对高的G’,而30-K组分G’降低。DH8.8%的Protamex酶解产物-阿拉伯胶在超声辐射条件下接枝时,接枝度(DG)最大;接枝物溶解性、热稳定性、乳化性和起泡性显著(P<0.05)提高,特别是ES增加更显著,溶解性曲线在pH3-10范围内平缓,没有明显的等电点;红外吸收光谱酰胺I带吸收峰发生部分偏移。改性面筋蛋白中游离SH/S-S比值升高,醇溶蛋白、可溶性麦谷蛋白及不溶性麦谷蛋白含量减少;改性面筋蛋白显微结构明显改变,β-折叠增加,α-螺旋/β-折叠比值下降,接枝物中α-螺旋/β-折叠比值最低,改性后面筋蛋白变性温度升高。分子分布及分子结构的改变引起蛋白分子柔韧性升高和表面性质改变,是改性面筋蛋白功能特性改善的重要原因。更多还原

【Abstract】 Wheat gluten is a byproduct of the wheat starch industry. The use in food is limited by its water-insoluble characteristic. The aim of the present study was to modify wheat gluten by enzymatic hydrolysis-membrane ultrafiltration fractionation (UF) for improving its functional properties and extending utilization. Optimal conditions and some intrinsic mechanisms of enzymatic hydrolysis were studied. Inhibition of gluten hydrolysate for enzymatic hydrolysis was investigated. The Enhanced functional properties of the modified glutens were evaluated. Graft reaction of gluten hydrolysate and polysaccharide subjected to ultrasound treatment was also investigated. Moreover, relation of composition/structure of the modified glutens to functional properties was analyzed.Five proteases (protamex, PTN6.0S, alcalase, neutrase and papain) were used to hydrolyze gluten protein and hydrolytic conditions were optimized. The contents of soluble nitrogen, amino nitrogen and peptide-based nitrogen in gluten hydrolysates were compared. Protamex was suitable for preparing the peptides with various molecular weight followed by Papain. According to SDS-PAGE and SE-HPLC analysis, gliadin and soluble glutenin were prone to degradation during enzymatic hydrolysis. Some of HMW-GS had resistance to hydrolysis.Wheat gluten subjected to thermal, extrusion, ultrasound and reducing agent led to change in its structure such as SH/S-S, hydrophicity / hydrophobicity. These pretreatment resulted in increase in degree of hydrolysis and protein recovery compared to control.Inhibition rate (IR) of gluten hydrolysates for enzymatic hydrolysis showed two distinct dynamic regions, DH-dependent and DH-independent region. The IR of gluten hydrolysate fractions obtained after UF had significant (P<0.05) difference. The peptides with below 5 kDa played dominant role in inhibition of enzymatic hydrolysis. Removal of these peptides was favor for enzymatic hydrolysis and maintenance of proteinase activity.The gluten hydrolysates were fractionated into 50-K, 30-K, 10-K and P fractions by membranes with different molecular weight cut-off. These modified glutens had different structure based on SDS-PAGE and FT-IR analysis. The enhanced (P<0.05) functional properties (solubility, water-holding capacity, emulsifying and foaming properties) of the gluten hydrolysates were found compared to original gluten. The enhanced functional properties were associated with DH of hydrolysates. Moreover, viscosity of the hydrolysates was influenced by its DH and concentration. Significant (P<0.05) increase in nitrogen soluble index at range of pH3-10 was found in the modified glutens compare with control. The pI of modified glutens shifted into acid or alkalin region. Low concentration of KCl and Cys can improve solubilization of the modified glutens. In addition, the thermal stability greatly improved. The modified glutens had better emulsion activity index, foaming capacity and water-holding capacity than the control sample, 30-K fraction had the highest value among these fractions. However, emulsion and foam stability decreased compared to control. Viscosity of the modified glutens decreased and increased with concentration of these proteins. Surface hydrophobicity of the modified glutens increased. The initial gel temperature of the modified glutens increased and decreased as ion strength increases. 50-K fraction had the highest storage modulus.The conjugate with the highest degree of graft using DH8.8% of Protamex hydrolysate and arabian gum could obtained. Optimal conditions of gluten hydrolysate and arabian gum for graft reaction were obtained by surface response design. Solubility, thermal stability, emulsifying and foaming properties of the resultant conjugate were significantly (P<0.05) improved compared the hydrolysate. Solubility curve kept relatively plateau at pH3-10. No obvious pI was noticed.The ratio of free SH/S-S of the modified glutens increased compared to control. Microstructure of the modified glutens had great change based on SEM observation. In secondary structure, modification led to decrease inα-helix/β-sheet ratio. The conjugate had the lowestα-helix/β-sheet ratio. Change in molecular weight distribution and structure of the modified gluten proteins resulted in improvement of flexibility and surface properties. These changes play an important role in improvement of functional properties.更多还原