INTERACTION BETWEEN PROTEIN AND LIPID IN SOYBEAN MILK AT ELEVATED-TEMPERATURE

Soymilk is prepared by heating swelled and ground soybeans, of which m ajor components are lipid and protein. The stability of lipid in aqueo us solution is important in soymilk. The interaction between lipid and protein in soymilk was studied from the viewpoint of changes in the l ipid and protein distribution by heating. Soymilk was fractionated to particulate, soluble, and floating fractions by centrifugation. Most o f the lipid in unheated soymilk existed in the particulate fraction. W hen heating from 65 to 75 degrees C, a part of lipid and almost alpha and alpha' subunits of beta-conglycinin in the particulate fraction li berated and moved to soluble fraction. When heating at 75 degrees C, t he lipids in the soluble and particulate fractions began to liberate a nd to shift to the floating fraction. Almost al lipid (neutral lipid) shifted to the floating fraction at 90 degrees C. The major proteins i n the floating fraction were two unknown proteins (named BX1 and BX2). BX1 and BX2 are minor proteins in soymilk and had relative molecular weights of 22000 and 16000, respectively.