Elucidation of a new fractionation method to understand the protein composition of soybean seeds

Two existing approaches facilitate the understanding of the role of soy protein in maintaining soybean product quality: the first involves the separation of the major protein fractions from the soybean seeds via various techniques, whereas the second compares products made from several soybean varieties with different protein contents and compositions. In this study, we developed a novel method of fractionating total soy proteins and determining the protein composition of soybean seeds. A high-salt concentration solution was used to extract whole proteins from non-defatted soybean powder. The total soybean protein was separated into four fractions, namely oil body-associated protein (OBAP), polar lipid-associated protein (PLAP), whey, and globulin, by combining the centrifugation step and adjusting solvent conditions. The protein content of each fraction was determined using the Dumas method, following which the protein distribution ratio was calculated. When the typical soybean cultivar Fukuyutaka was fractionated, the protein distribution ratios to OBAP, PLAP, whey, and globulin were 15.7, 10.5, 16.1, and 52.7, respectively. This method is more efficient than earlier approaches for analyzing and comparing protein composition and quantity in fractions obtained from multiple varieties of soybean.