基于高场强超声波对大豆蛋白的“降聚增活效应”探讨其增强冷凝胶性的机理

Even though the amount of soy protein of China is abundant, the soy protein product of China is single variety. Soy protein is able to form cold gel, which is benefit for protection of heat-sensitive compounds in the gel. Therefore, if the cold gelation property of soy protein can be enhanced, soy protein products’ variety will increase. Recently, we noticed that high intensity ultrasound (HIU) increased the cold gelation property of soy protein significantly. However, the mechanism of why HIU can increase soy protein cold gelation property is not well reported. The cold gelation property of soy protein is determined by its aggregation state and structure. Therefore, the “reduce aggregation and increase activity phenomenon” of HIU treated soy protein is a great help for explaining soy protein’s cold gelation property enhancing mechanism. In this program, acid-induced aggregated soy protein, ethanol-induced aggregated soy protein as well as heat and water denaturation-induced aggregated soy protein will be produced as research raw materials. Firstly, researches will be carried out to evaluate how HIU influence soy protein cold gelation property. Furthermore, the relationship between “reduce aggregation and increase activity phenomenon” of HIU treated soy protein and the improvement of cold gelation property of soy protein will be described. The above information is benefit to show the cold gelation enhancing mechanism from the view of materials changes before gel formation. Moreover, the effects of HIU on soy protein cold gel formation process and gel structure will be studied based on the changes of some important aspects, namely the key factors of gel formation, gel formation speed, protein intermolecular force, conformation of protein, protein aggregation state and 3D structure of protein gel network. The relationships between cold gelation property improvement and the changes of the above important aspects will be discussed, so as to reveal the cold gelation enhancing mechanism from the views of materials changes during gel formation and after gel formation. In a word, the above studies may facilitate the application of HIU in soy protein industry.

我国大豆蛋白资源丰富，但品种单一。大豆蛋白能形成冷凝胶，可保护添加的热敏物质，如能增强其冷凝胶性，开发高冷凝胶性产品，可丰富大豆蛋白品种。我们近期发现，高场强超声波（HIU）能增强大豆蛋白冷凝胶性，但机理不明。大豆蛋白的聚集状态和结构决定其冷凝胶性，因此HIU对大豆蛋白的“降聚增活效应”成为阐明HIU增强大豆蛋白冷凝性机理的突破口。本项目以酸诱导、醇诱导和湿热诱导所形成的三种大豆蛋白为原料，探寻HIU对大豆蛋白冷凝胶性的改变规律，揭示HIU对大豆蛋白的“降聚增活效应”与冷凝胶性的关系，从凝胶形成前物质变化的角度，探讨冷凝胶性增强机理。然后，根据诱导凝胶关键指标、凝胶速率、聚集体状态、分子间作用力、蛋白构象和凝胶空间结构的变化与冷凝胶性的关系，阐明HIU对大豆蛋白冷凝胶形成过程和凝胶结构的影响，从凝胶形成时和凝胶体物质变化的角度，探讨冷凝胶性增强机理。最终，拓展HIU在大豆蛋白加工中的应用。

研究表明，在20kHz频率下，随超声处理时间增加，大豆分离蛋白的粒径和浊度减小，溶解度增大，二三级结构改变，表面疏水性增强，非共价键作用明显增强，总巯基含量减少，二硫键增加，“降聚增活效应”显著增强，经过相关性分析，“降聚增活效应”与冷凝胶性呈正相关。高场强超声波可改变大豆分离蛋白的二级结构和三级结构，暴露更多疏水基团，增加疏水环境和表面疏水性，大豆蛋白分子间的非共价作用增强，当加入促凝剂后，可以形成更多的非共价键或共价键，形成更加致密、均一的微观凝胶结构，从而增加冷凝胶的持水性和凝胶强度。分别以酸变性、醇变性、湿热变性大豆分离蛋白为原料，发现高场强超声对三种变性大豆分离蛋白冷凝胶性的影响不同。短时间超声仅使热变性大豆分离蛋白冷凝胶形成且凝胶强度无显著变化，而较长时间超声处理后的三种变性大豆分离蛋白均可以形成冷凝胶，且随超声时间增加凝胶强度增强。此外，研究还发现大豆蛋白重要组分（7S和11S）在HIU环境下的结构、性质和降聚增活效应受溶液环境的影响极其显著。总之，高场强超声技术可有效提高大豆分离蛋白的冷凝胶性，但其具体效果受蛋白变性方式及超声作用环境影响显著。