Study on variation of nutritional value of soy protein isolate after being processed into films

Abstract

采用胃蛋白酶和２，４，６－三硝基苯磺酸分别测定大豆分离蛋白膜的消化率和赖氨酸有效性。结果表明，蛋白质的消化率和赖氨酸有效性随成膜溶液的ｐＨ升高而下降，并因一些增加蛋白质交联的物质如单宁、阿魏酸和过氧化氢的添加而降低。蛋白膜的机械特性与膜蛋白消化率和赖氨酸有效性存在一定负相关，即机械性能较强的膜，其消化率和赖氨酸有效性较低。不过，玉米淀粉似乎是个例外，它在改善膜机械特性的同时，也保持了大豆蛋白膜的营养。由于大豆分离蛋白制备成膜后，其消化率和赖氨酸有效性下降，因此将大豆蛋白膜称为生物可降解膜似乎比称作可食性膜更科学。 Pepsin and 2,4,6-trinitrobenzenesulphonic acid were used to test in vitro the soy protein isolate digestibility and the content of reactive lysine of film proteins respectively. The results showed that in vitro protein digestibility and content of reactive lysine of film proteins decreased with increase in pH of film forming solution and addition of cross-linking agents such as tannin, ferulic acid and hydrogen peroxide, also with increase of mechanical properties of films. However, cornstarch seemed an exclusive, which increased the mechanical properties of films but almost kept unchanged in vitro protein digestibility and the content of reactive lysine of film proteins. It can be concluded that the nutritional value of soy protein isolate decreased after it was used to prepare film. Thus, it appeared that it was more reasonable to make films prepared from soy protein isolate as biodegradable films rather than as edible films.