Soymilk is prepared by heating swelled and ground soybeans, of which major components are lipid and protein. The stability of lipid in aqueous solution is important in soymilk. The interaction between lipid and protein in soymilk was studied from the viewpoint of changes in the lipid and protein distribution by heating. Soymilk was fractionated to particulate, soluble, and floating fractions by centrifugation. Most of the lipid in unheated soymilk existed in the particulate fraction. When heating from 65 to 75 °C, a part of lipid and almost α and α‘ subunits of β-conglycinin in the particulate fraction liberated and moved to soluble fraction. When heating at 75 °C, the lipids in the soluble and particulate fractions began to liberate and to shift to the floating fraction. Almost all lipid (neutral lipid) shifted to the floating fraction at 90 °C. The major proteins in 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.
Keywords: Soymilk; lipid; heating