Bio-conversion of Liquiritin and Liquiritin Apioside from Glycyrrhiza uralensis Root to Liquiritigenin during Nuruk Fermentation

Phytochemical researches on Glycyrrhiza uralensis root have revealed the existence of abundant polyphenol glycosides such as liquiritin and liquiritin apioside. On the basis of earlier reported researches, we could expect that Glycyrrhiza uralensis root is a medicinal herb useful for polyphenol preparation as well as its polyphenol glycosides will be converted to the corresponding aglycones, which have more active form in skin biology, by employing Nuruk fermentation. As expected, HPLC results revealed that the polyphenol glycosides obviouslyunderwent deglycosidation reaction during Nuruk fermentation, thereby indicating that Aspergillus niger and Aspergillus oryzae, major fungi in Nuruk, are very effective in bioconverting vegetable polyphenol glycosides to alycones. As such results, increase of liquiritigenin peak was evidently observed together with simultaneous decrease of each two peak corresponding to liquritin and liquiritin apioside. The conversion rate was more than 95% and the chemical structure ofliquiritigenin was confirmed by NMR analysis. These results indicated that Nuruk fermentation is a good method to prepare in high yield liquiritigenin, an estrogenic substrate. Koji acid, a direct tyrosinase deactivator, was also identified by HPLC analysis. Thus, the final Nuruk ferment will function skin whitening and wrinkle prevention. Like this, combining two or more agents via different active mechanisms in a raw material for cosmetics preparation will contribute to furtherimprovement of skin beauty.