Free and bound form bioactive compound profiles in germinated black soybean (Glycine max L.)

This study investigated the transition between the free and bound forms of functional compounds in germinated black soybean. Black soybean was germinated at 25°C over 6 days and then the free and bound forms of functional compounds were extracted. Total free polyphenol, flavonoid, and phenolic acid contents in raw black soybean increased from 1.03 mg GAE/g, 0.29 mg CE/g, and 315.67 μg/g to 1.44mg GAE/g, 0.64mg CE/g, and 511.01 μg/g, respectively, by 4 days after germination. Changes to phenolic acid compositions can be divided into four groups, and the germination process can convert compounds to phenolic acid via anabolism and catabolism. The highest total free isoflavone content in germinated black soybean (3,724.40 μg/g) was observed at 4 days. Bound polyphenol, flavonoid, phenolic acid, and isoflavone contents decreased as the germination period increased. These results suggest that the germination process increased compound functionality in black soybean.