In vivo bioavailability of essential minerals and phytase activity during soaking and germination in soybean (Glycine max L.)

Dietary quality is an important limiting factor for proper nutrition in many resource poor settings, with a major concern, micronutrient bioavailability. High content of phytate present in soybean (Glycine max. L) chelates divalent essential mineral ions and reduces its bioavailability and thus dictates the nutritional role of this wonder crop. In this study, the changes in phytate, phytase activity and bioavailability of essential minerals (Fe, Zn,Ca) were investigated using various colorimetric assays, AAS and functionally validated using an in vivo simulation model in two Indian cultivars, Pusa 9712 and Kalitur after soaking and germination. Phytate-mineral ratio, another parameter for bioavailability was also analyzed. Phytate content was reduced to 10-13% after 12 hrs of soaking and a further reduction to 46-65% was observed after 72 hrs of germination in Kalitur and Pusa 9712, respectively. Phytate being mainly hydrolyzed by phytase, we observed a six-fold increase in its activity after 72 hrs of germination, compared to control. Considering the dietary role, using an in vivo mimicking approach, a significant increase in the bioavailability of Fe(8-21%), Zn (7-18.5%) and Ca (8-24%) in Kalitur and 9-27% (Fe), 9-25% (Zn) and 9-23% (Ca) in Pusa 9712, respectively was observed after 72 hrs of germination. A negative correlation (p ≤ 0.05) was observed between phytate and mineral bioavailability in sprouted soybean seeds. Thus soybean sprouts enhance the nutritional quality by lowering the anti-nutrient contents and increasing the bioavailability of minerals.