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Phytic acid and phosphorus content of various soybean protein fractions

Honig, D.H., Wolf, W.J., Rackis, J.J.
Cereal chemistry 1984 v.61 no.6 pp. 523
soybeans, soy protein, phytic acid, phosphorus, nutrient content, protein isolates, globulins, food composition
Phytate-protein complexes formed during the manufacture of soy protein isolates reportedly affect mineral bioavailability in foods; the amounts of such complexes were estimated by determining the phytic acid (PA) content by anion-exchange high-performance liquid chromatography (HPLC) before and after dialysis. Protein fractions analyzed include: commercial soybean protein isolates; laboratory-prepared isolates; the 2 major components of the isolates, the 7S and 11S globulins; the pH 8 insoluble material formed on neutralization of the isoelectric (pH 4.5) form of the isolate; and the pH 8 soluble fraction of the isolate. After dialysis, the PA content of the various soybean protein isolates was 0.95-1.75%. The 11S globulins were essentially devoid of PA, while the 7S globulins contained 0.34%. PA values for the dialyzed pH 8 insoluble and soluble protein fractions were 0.22-1.41% and 0.36-1.29%, respectively. Yields of the pH 8 insoluble fractions were 10.2-28.6% of the total protein isolate. Certain protein components of the soybean protein isolate are strongly complexed with phytic acid, especially at pH 8. Variability in the nature and yield of the insoluble proteins and in the amount of phytic acid bound indicates that factors other than the pH and protein type are involved in the formation of phytate-protein complexes. Processing conditions appear to be important, because extensive dialysis of the commercial samples at pH 8 failed to remove appreciable amounts of phytic acid.