Effect of UV-B Irradiation on Contents of Ergosterol, Vitamin D2 and other Nutrients in Thai Edible Mushrooms

Abstract

Fruiting bodies, mycelia and freeze - dried powder of nine commercial types of mushrooms in Thailand including enoki, eryngi, khonkao, kradang, jew’s ear, oyster, phoenix, shiitake and yamabushitake were irradiated with ultraviolet-B (UV-B) to investigate the conversion of ergosterol to vitamin D2 and the responses of vitamin B1 and vitamin B2 in fresh mushrooms were also analyzed after treatment. After exposed to UV-B for 15 to 180 min, at each time point, the concentration of ergosterol in fresh mushrooms was decreased whereas the amount of vitamin D2 was increased. The conversion to vitamin D2 was most in oyster (27.89±0.67 mg/g dry weight) but least in eryngi (4.54±0.02 mg/g dry weight) among the nine mushrooms. Vitamin B1 concentration in all fresh mushrooms remained relatively stable after UV-B irradiation but vitamin B2 content decreased. Prolonged irradiation (60 to 180 min) led to discoloration in fresh enoki. Additionally, mycelia and lyophilized mushrooms powder were also subjected to the UV-B exposure for ergosterol to vitamin D2 inversion.