The effects of sodium phytate and partially hydrolyzed sodium phytate (0 -82% hydrolyzed) on pepsin digestion of casein and bovine serum albumin were evaluated by an in vitro procedure using dialysates of pepsin digestion over a period of 0 -23 hr. The inhibitory effect of phytate differed with substrate and increased with dose level. At the highest phytate level, the digestion of casein and bovine serum albumin was reduced by 14% and 7%, respectively. The inhibitory effect of the phytate was inversely correlated with the degree of phytate hydrolysis. Hydrolysis for 16 hr almost eleminated the inhibitory effect of phytate.

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Effects of phytate and its hydrolysis products (myo-inositol phophate esters) on protein digestion were investigated by in vitro and in viva procedures. Tri-, tetra-, penta-, and hexa-phosphate ester fractions, isolated from phytate hydrolysates, inhibited pepsin digestion of casein and bovine serum albumin in vitro. The inhibition ranged from 0% for the mono-and diphosphate esters to 9-14% with the hexdphosphate ester (phytate). The phosphate ester fractions did not significantly affect trypsin digestion of the proteins. In the in vivo study, rats were fed phytate and hydrolysates thereof (mixtures of the esters above) at levels of l-3.5% of the diet. Under the conditions of this study, neither phytate nor its hydrolysates significantly affected protein utilization or weight gain in rats.

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