A product resulting from the biotransformation of genistein by a recombinant Pichia pastoris was isolated and identified as 3'-hydroxygenistein, on the basis of mass, H-1 NMR, and C-13 NMR spectrophotometric analysis. The maximal product concentration and the conversion yield of the biotransformation in a 51 fermenter were 3.5 mg/1 and 14%, respectively. The inhibitory effects of 3'-hydroxygenistein on tyrosinase activity were investigated in vitro using mushroom tyrosinase. The results showed that 3'-hydroxygenistein potently inhibited tyrosinase activity with an IC50 value of 15.9 mu M. Furthermore, the inhibitory effects of 3'-hydroxygenistein on melanogenesis were also investigated in vitro in cultured B16 melanoma cells, and it was shown that 3'-hydroxygenistein dose-dependently inhibited melanogenesis in non-toxic concentrations. In summary, the 3'-hydroxygenistein that was produced from genistein by the recombinant yeast was confirmed as a potent tyrosinase inhibitor and inhibited melanogenesis in B16 cells. (C) 2015 Elsevier Ltd. All rights reserved.