Antioxidant and tyrosinase inhibitory activities from seed coat of brown soybean

Soybeans with brown, black, and yellow seed coats were compared to total phenolic contents and antioxidant activities including 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radicals. Also, 3 seed coats were examined for inhibitory activities on tyrosinase and lipoxygenase-1 on the basis of spectrophotometric and polarographic methods. Among seed coat extracts, 80% methanol extract of brown soybean seed coat showed the highest total phenolic contents (68.9 +/- 3.29 mg GAE/g) as well as exhibited potent scavenging effects on the DPPH (IC50 = 4.3 mu g/mL) and ABTS (IC50 = 3.7 mu g/mL) radicals. In a polarographic experiment, this extract was potentially inhibited the oxidation Of L-tyrosine and L-3,4-dihydroxy-phenylalanin (L-DOPA) catalyzed by mushroom tyrosmase with IC50 values of 12.4 and 63.7 mu g/mL, respectively. It was also detected inhibition of the tyrosinase catalyzed oxidation of L-DOPA with an IC50 value of 120.3 mg/niL in UV spectrophotometric experiment. In addition, this extract inhibited the linoleic acid peroxidation catalyzed by lipoxygenase-1 with an IC50 value of 4.0 mu g/mL. These results suggest that brown soybean may possess more beneficial effect on human health than black and yellow soybeans.