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.
Soybeans stored under 4 conditions were analyzed for the degradation of phytate and its effects on tofu qualities. Phytate in soybeans was hydrolyzed significantly under the adverse conditions for 9 ...mo, but decreased slightly under 3 mild conditions for 18 mo. Phytate degradation contributed to an increase in titratable acidity. When the phytate contents of soymilk were selectively reduced by 11.3% and 17.5% by phytase, while other components remained unchanged, tofu yield increased significantly but texture became softer. Tofu yield decreased and hardness increased in beans stored in the adverse conditions. Phytate degradation during adverse storage played a minor, indirect role in the deterioration of soybeans for tofu making.
