Simple Freeze-thaw Fractionation of 7S and 11S Globulins in Soymilk

Abstract

7S and 11S globulins are major components of soybean protein. We developed a new simple freeze-thaw method for crude fractionation of these proteins in soymilk. Raw, unheated soymilk was frozen at -30°C, and then thawed at 10°C for 24h. The freeze-thawed soymilk separated into two layers, and the weight ratio of the upper layer (UPL) and the down layer (DOL) was 3 : 2. By SDS-PAGE analysis, the ratio of 7S to 11S globulins was 1 : 0.14 in the UPL, and 1 : 1.7 in the DOL. We mixed UPL with DOL in various ratios, and tofu curds were made from these mixtures. The breaking stress of the tofu curd increased with increased DOL ratios. The curd made from UPL was soft and smooth, and a novel dessert-like product was made via coagulation with yuzu juice. Through sensory evaluation, the product made using only UPL was tasty. These results show that rough separation of 7S and 11S globulins in raw soymilk can be achieved by a simple freeze-thaw treatment, and can lead to the development of new food products.