Oyster mushroom (Pleurotus ostreatus Fries.) is rich in nutrition and has many medicinal properties such as antioxidant and anticancer activities. It also contains a high amount of ergosterol which can be converted to vitamin D2 when exposing to UV light. Oyster mushroom powder was irradiated with UV-B for 180 min and extracted with 95% ethanol. Mushroom extract was determined for vitamin D2 concentration, total phenolic compound, antioxidative activity, tyrosinase inhibitory property and cytotoxicity effect on human keratinocytes (HaCaT) and murine melanoma cells (B16F10) by MTT assay. The results demonstrated that the concentration of vitamin D2 of irradiated oyster mushroom extract was 153.96 µg/g, which is 13 times higher than that of non-irradiated mushroom extract. Total phenolic content, antioxidative and tyrosinase inhibitory activities of the two mushroom extracts were not significantly different. Neither oyster mushroom extract had a cytotoxic effect on keratinocytes, but on the other hand both inhibited the growth of murine melanoma cells.
