Availability to rats of zinc in green and mature soybeans

A slope ratio assay was conducted with young albino rats to investigate the effect of maturity of soybean seeds on the bioavailability of their intrinsic zinc. Seeds (Williams) were harvested when well-developed but green (25% dry matter) and when mature (86% dry matter). The blanched seeds were wet-milled, freeze-dried and incorporated into 20% egg white protein diets at the expense of egg white to provide 20% protein diets containing equal calories and calcium but varying in zinc and phytate content. Zinc in the mature bean flour diets was 58% as available for weight gain and 57% as available for tibia zinc accumulation as was zinc in the green bean flour diets. The difference between zinc availabilities can be ascribed to the higher phytate content of the mature beans.