Enhancement of zinc utilization from phytate-rich soy protein isolate by microbial phytase

A study with three groups, each with 11 male, individually housed albino rats (initial average weight = 50 g) was undertaken to examine the effect of microbial phytase (added to a diet containing phytate) on the availability of zinc. The rats were fed diets on the basis of soy protein isolate and corn starch over a 3-week period. All diets contained 15-16 mg Zn/kg diet and 0.40% PA. Thus, molar PA:Zn-ratios of 26:1 were obtained. Group I (control) was fed the phytase-free basal diet. In groups II (pair-fed to group I) and III, 1,000 U of microbial phytase (Aspergillus niger var. van tighem) per kg diet were added. Some rats fed the phytase-free basal diet (control) showed typical symptoms of zinc deficiency, including cyclic changes in food intake, anorexia and partial alopecia. By the addition of 1,000 U microbial phytase the apparent absorption of zinc (percent of intake) significantly increased from 33% (control) to 63% (1,000 U, pair-fed) and 66% (1,000 U, ad lib.). Similar positive effects of the phytase-supplementation were observed for three zinc status parameters in plasma, zinc-concentration, percent unsaturated zinc-binding capacity, activity of alkaline phosphatase and the zinc-concentration in femur and testes. The present study shows that an addition of microbial phytase to phytate-rich diets based on soy protein isolate considerably improves the availability of zinc in growing rats.