Sunday, July 24, 2011
Grand Ballroom, 5th fl (Sheraton New Orleans)
Hydroquinone galactoside (HQ-Gal) as a potential skin whitening agent was synthesized by the reaction of lactase (β-galactosidase) from Kluyveromyces lactis, Aspergillus oryzae, Bacillus circulans and Thermus sp. with lactose as a donor and HQ as an acceptor. Among these lactases, the acceptor reaction involving HQ and lactose with K. lactis lactase showed a higher conversion ratio to HQ-Gal (60.27%). HQ-Gal was purified using butanol partitioning and silica-gel column chromatography. The structure of the purified HQ-Gal was determined by nuclear magnetic resonance and the ionic product was observed at m/z 295 (C12H16O7 Na)+ using matrix assisted laser desorption ionization time-of-flight mass spectrometry. HQ-Gal was identified as 4-hydroxyphenyl-β-D-galactopyranoside. The optimum conditions for HQ-Gal synthesis by K. lactis determined using response surface methodology were 50 mM HQ, 60 mM lactose and 20 U mL-1 lactase. These conditions produced a yield of 2.01 g L-1 HQ-Gal. The half maximal inhibitory concentration (IC50) of diphenylpicryl-hydrazyl scavenging activity was 3.31 mM indicating a similar anti-oxidant activity compared to β-arbutin (IC50 = 3.95 mM). The Ki value of HQ-Gal (0.75 mM) against tyrosinase was smaller than that of β-arbutin (Ki = 1.97 mM), indicating its superiority as an inhibitor. HQ-Gal inhibited (23%) melanin synthesis without being significantly toxic to the cells, while β-arbutin exhibited only 8% reduction of melanin synthesis in B16 melanoma cells compared with the control. These results indicate that HQ-Gal may be a suitable functional component in the cosmetics industry.