Optimization of extraction and isolation for 11S and 7S globulins of soybean seed storage protein

A new method was developed for extraction and isolation of 7S and 11S fractions from soybean seed, based on methods of Nagano et al., Thanh and Shibasaki [Nagano, T., Hirotsuka, M., & Mori, H. (1992). Dynamic viscoelastic study on the gelation of 7S globulin from soybeans. Journal of Agricultural and food chemistry 40, 941–944 and Thanh, V. H., & Shibasaki, K. (1976). Major proteins of soybean seeds. A straightforward fraction and their characterization. Journal of Agricultural and Food Chemistry 24, 1117–1121]. Optimization of the extraction and isolation of 11S and 7S globulins from soybean seed was investigated under various conditions by the Kjeldahl method and SDS-PAGE. The optimal conditions were as follows: 0.03–0.06 M Tris–HCl buffer (pH 8.5) containing 0.01 M sodium bisulfite as extract solution, extraction twice at 45 °C for 1 h, and with a 1:15 ratio (w/v) of flour:Tris–HCl. The 11S fraction was precipitated at pH 6.4, and the supernatant, after centrifugation, was adjusted to pH 5.5 to remove the insoluble intermediate fraction by further centrifugation. The supernatant obtained was then adjusted to pH 4.8 to afford the 7S fraction as a precipitate by centrifugation. With the improvements, the protein contents and purities of the isolated 11S and 7S fractions were significantly increased. The contents of all subunits of the isolated 11S and 7S fraction were markedly higher than those by Thanh and Shibasaki method, while the contents of α, β and B3 were also significantly higher than those by Nagano et al. method.