Liquiritigenin and isoliquiritigenin are the major flavonoids present in licorice. These flavonoid compounds were prepared by submerged culture of Grifola frondosa (G. frondosa) HB0071 mycelia producing β-glucosidase in the aqueous extract of licorice. The contents of liquiritigenin and isoliquiritigenin were increased during the fermentation. This fungus produced a high β-glucosidase (activity of 91.5 mU/mL), thereby achieving high amounts of liquiritigenin and isoliquiritigenin (568.5 µg/mL and 89.6 µg/mL), respectively at 96 h. A reversed-phase high-performance liquid chromatography method was established for simultaneous determination of liquiritigenin and isoliquiritigenin in fermented licorice extract (FLEx). The anti-inflammatory activities were investigated by licorice extract (LEx) before and after fermentation with G. frondosa HB0071. The treatment of UVB-irradiated HaCaT keratinocytes with FLEx resulted in a dose-dependent decrease in the expression level of cyclooxygenase-2 (COX-2) mRNA. Furthermore, FLEx dose-dependently decreased mRNA of the pro-inflammatory cytokines of IL-1β and IL-6 in UVB-irradiated HaCaT cells. These results suggest that FLEx may mitigate the effects of skin inflammation by reducing UVB-induced adverse skin reactions.
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