Antioxidant and tyrosinase inhibitory activities from seed coat of brown soybean

Abstract

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.