Impact of soaking, germination, fermentation, and roasting treatments on nutritional, anti-nutritional, and bioactive composition of black soybean (Glycine max L.)

Legumes are plants of the family Leguminosae with seed pods that split into two halves. Black soybean seed coat contains numerous bioactive compounds having radical scavenging, anti-tumor, and anti-carcinogenic activities. This study was aimed to assess the effect of soaking, germination, natural fermentation, and roasting on nutritional and antinutritional components, minerals (Fe, Zn, Mn, and Cu), and bioactive components of the black soybean. The effect of soaking was studied at 12 and 24 h while that of germination at 24, 48, and 72 h. The results revealed that the phenolic contents augmented significantly ( P ≤ 0.05) in germination, fermentation, and roasting by 11.49%, 8.96%, 2.95%. Further, there was an 11.84% and 22.13% increase in the protein contents during the germination and fermentation processes, respectively. The antioxidant activity of processed grains increased significantly ( P ≤ 0.05) during germination, fermentation, and roasting by 72.51, 10.14, and 9.64%, respectively. The anti-nutritional compounds such as phytic acid and tannin contents decreased significantly ( P ≤ 0.05) during processing treatments. Phytic acid decreased to the extent of 34.04, 51.06, and 13.47% and tannin contents as 47.22, 75, and 38.89%, after germination, fermentation, and roasting processes, respectively. A significant ( P ≤ 0.05) increase in mineral contents was observed after the germination, fermentation, and roasting of the black soybean.