Soybean products, phytic acid

Contamination of soybeans with Aspergillus flavus is found in approximately 50% of commercial samples. Fortunately, the incidence of aflatoxin from this route is quite low. Moisture at [he time of maturity, development of the seed in a closed pod, and binding of zinc by phytic acid are suggested as reasons for resistance of soybeans to aflatoxin production... 

Phytic Acid. Recent reviews (67,68,69) summarized the literature covering the relationship between phytic acid and mineral bioavailability in soy protein products. The formation of phytate-proteln-mineral complexes (particularly zinc chelates in flours, concentrates, and Isolates prepared from mature soybeans) may be responsible for reduced mineral availability. However, the iron in Fe-labeled mature soybeans is more available to iron-deficient rats than the iron in green-immature soybeans, even though mature soybeans contain three times more phytic acid (70). The factor(s) responsible for this difference in bioavallablllty has not been identified. 

Zhou JR, Fordyce CJ, Raboy V, et al. 1992. Reduction of phytic acid in soybean products improves zinc bioavailability in rats. J Nutr 122(12) 2466-2473. 

Phytic acid and camosine (histidine-containing dipeptide), obtained from cereal and meat by-products, are effective inhibitors of hpid oxidation by several mechanisms, including metal inactivation and free radical quenching. Uric acid obtained from the decomposition of adenosine triphosphate in muscle also inhibits lipid oxidation by the same mechanisms. However, the importance of uric acid as an endogenous antioxidant in muscle foods is not clear. Various protein concentrates from soybeans, cottonseed and peanuts inhibit hpid oxidation in muscle foods. In addition to their iron binding activity, these crade extracts contain complex polyphenolic flavonoids that have potent antioxidant activity. 

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