美拉德反应制备等电点澄清透明的乳清分离蛋白研究

Study on the Preparation of Transparent Whey Protein Isolate at Isoelectric Point by Maillard Reaction

摘要:

本文旨在以乳清分离蛋白(WPI)为原料，研究其与糖类物质的美拉德反应制备得到产物在等电点附近的溶解性、乳化性（EAI）、乳化稳定性（ESI）和热稳定性等功能特性，为其在透明饮料中的应用奠定基础。在相对湿度79%，温度70 ℃的反应条件下制备得到乳清分离蛋白与L-乳糖的美拉德反应产物，聚丙烯酰胺凝胶电泳(SDS-PAGE)实验结果证实了美拉德反应使WPI中α-乳清蛋白和β-乳球蛋白分子量分别增加2~3 ku左右；邻苯二甲醛(OPA)结果表明在美拉德反应时间为12 h时，WPI中游离氨基酸含量减少35%左右；美拉德反应改性使其溶解性、乳化性（EAI）、乳化稳定性（ESI）和热稳定性都有显著提高（在10 min时EAI和ESI分别为0.35 m2/g和20 min，为WPI的1.5倍和1.7倍）；电位和粒径结果显示，乳清分离蛋白糖基化产物的溶解性和热稳定性增强是因为蛋白质表面引入糖分子的位阻效应所致，而非静电作用。

Abstract:

Whey protein isolate (WPI) was used as the raw material for this study. The solubility, emulsifying activity index (EAI), emulsifying stability index (ESI), thermal stability, and other functional properties of WPI and its Maillard reaction products (MRPs) around the isoelectric point were studied, to lay a basis for their application in transparent-type beverages. The MRPs of WPI and L-lactose were formed by the reaction between WPI and L-lactose at a relative humidity of 79% and a temperature of 70 ℃. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results suggested that the molecular weights of α-lactalbumin and β-lactoglobulin were increased by about 2~3 ku. The o-phthalaldehyde (OPA) results showed that the free amino acid content in WPI was reduced by about 35% after the Maillard reaction for 12 h. The solubility, EAI, ESI, and thermal stability were enhanced remarkably (EAI and ESI were 0.35 m2/g and 20 min, respectively, which were 1.5 times and 1.7 times as much as those of WPI). Zeta-potential and particle size analysis indicated that the enhancement of the solubility and thermal stability of the MRPs was induced by the steric hindrance of the saccharides introduced to the protein surface, instead of the electrostatic interactions.