Variation in the phytic acid content of soybeans and its effect on consistency of tofu made from soybean varieties with high protein content

The relationships of contents of phytic acid and protein to the breaking stress of tofu were examined using soybeans of three Japanese varieties with high protein content harvested in different locations from the years 2001 to 2003. The phytic acid content was more variable than protein content within different cultivating locations and years for the same variety and showed significant negative correlation to the breaking stress of tofu made with 0.25% MgCl2 for all the varieties (P < 0.001, r = -0.60). In particular, Sachiyutaka variety was characterized by the highest negative correlation between the breaking stress of tofu and the phytic acid content in soymilk (P < 0.001, r = -0.73). As MgCl2 concentration increased, the correlation between the phytic acid content and the breaking stress of tofu was reduced, and finally there was no significant correlation between them when the breaking stress reached a maximum at the particular MgCl2 concentration which is probably concerned with varietial characteristics of soybeans. These results support the idea that the variation in the content of phytic acid, which can act as a buffer against coagulation of soy protein, accounts for the fluctuation in consistency of tofu made with lower MgCl2 concentrations (ca. 0.25%) using soybeans of the same variety with different cultivating conditions. (c) 2005 Society of Chemical Industry.