Studies On Effects Of Extracts Of Mulberry On Inhibition Of Tyrosinase

In humans and other mammals, the biosynthesis of melanins takes place in a lineage of cells known as melanocytes, which contain the enzyme tyrosinase. Tyrosinase (phenol oxidase) is known to be a rate-limiting enzyme in the process of melanin biosynthesis. It can catalyze the oxidation of L-tyrosine in epidermal melanocytes to melanin finally. So the development of tyrosinase inhibitors has become increasingly important in cosmetics and medicinal area. The most effective compound for inhibiting tyrosinase activity from mulberry was traced and isolated with the yield and the relative inhibitory activity against tyrosinase of the extract used as evaluating indexes in this dissertation.The inhibition of tyrosinase by extracts from leaves and root cortices of mulberry were determined. The result was that root cortices of mulberry were the best source of tyrosinase inhibitor. Then root cortices of mulberry were extracted consecutively with solvents of increasing polarity in order to find the polarity of tyrosinase inhibitor. It was found that Ethanol was chosen to be best solvent for extraction.The effect of extraction technology on inhibiting tyrosinase activity from root cortices of mulberry was studied with the yield and the inhibitory ratio against tyrosinase of the extract used as evaluating indexes in the dissertation. The effect of ethanol concentration, extraction time, extraction temperature and pH on the inhibitory ratio and the yield of the extracts were researched in the experiment. Then orthogonal design was used for the research. From the value of variance analysis, the maximal factor that impacts the inhibitory ratio of tyrosinase inhibitor is the extraction temperature, while the main factor impacting yield is the concentration of ethanol. The optimum extraction process was as follows:root cortices of mulberry was extracted by55%ethanol at60℃for2times, each time for2hours and pH=6.8. The result was that the average of inhibition of tyrosinase activity was72.92%and the average of yield was27.90%for repeat experiment.The tyrosinase inhibitor was traced and isolated with chromatographic separation and used preparative HPLC for purification. The structures of purified compounds were elucidated by various spectroscopic methods:UV, IR, MS,1H NMR and13C NMR. It was identified as sanggenon C finally. Its activity of tyrosinase inhibition (96.23%) was better than traditional inhibitor arbutin.