Characterization of storage proteins in different soybean varieties and their relationship to tofu yield and texture

The contribution of the total soybean proteins, the storage proteins [glycinin (11S) and β-conglycinin (7S) fractions] and their respective subunits to tofu yield and texture was studied. Protein contents were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) coupled with densitometry and reversed phase-high performance liquid chromatography (RP-HPLC), for seven soybean varieties, and correlated to tofu yield and texture. Results from SDS-PAGE, coupled with densitometry, showed that the 11S fraction proteins (r=0.863, P<0.01), the α′ polypeptide of 7S (r=0.917, P<0.01) and the basic polypeptide of 11S (r=0.775, P<0.01) appeared to each affect tofu yield; however, no relationship between storage protein fractions and tofu firmness was observed. On the other hand, the RP-HPLC profiles of the total soybean proteins and the 11S and 7S fractions indicated relationships between tofu firmness and the 11S fraction, the 7S fraction, and their ratio. The inverse correlation (r=−0.832, P<0.01) between peak 7 of the 7S fraction and tofu firmness seems to point toward its important role in defining tofu quality.