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 ($68.9{\pm}3.29\;mg$ GAE/g) as well as exhibited potent scavenging effects on the DPPH ($IC_{50}=4.3\;{\mu}g/mL$) and ABTS ($IC_{50}=3.7\;{\mu}g/mL$) 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 tyrosinase with $IC_{50}$ 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 $IC_{50}$ value of 120.3 mg/mL in UV spectrophotometric experiment. In addition, this extract inhibited the linoleic acid peroxidation catalyzed by lipoxygenase-1 with an $IC_{50}$ 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.