Ultraviolet Irradiation Increased the Concentration of Vitamin D and Decreased the Concentration of Ergosterol in Shiitake Mushroom () and Oyster Mushroom () Powder in Ethanol Suspension.

Vitamin D deficiency is a serious global health problem. Edible mushrooms are a good source of vitamin D for human health. The objective of this experiment was to investigate the efficiency of converting its precursor ergosterol to vitamin D in shiitake mushroom () and oyster mushroom () powder in ethanol suspension under ultraviolet (UV) irradiation. UV irradiation conditions were optimized for several parameters, such as material form, wavelength, wavelength combination, and exposure time. Under the optimal conditions, UV irradiation increased the concentrations of vitamin D from undetectable to 40.59 ± 1.16 μg/g (dw) in dry shiitake mushroom powder and to 677.28 ± 40.42 μg/g (dw) (an approximately 16.69-fold increase) in ethanol suspension. The concentration of vitamin D increased from undetectable to 23.71 ± 5.72 μg/g (dw) in the dry oyster mushroom powder upon UV irradiation, whereas UV irradiation increased the concentration to 275.32 ± 48.45 μg/g (dw) (an approximately 11.61-fold increase) in the ethanol suspension. Comparing the effects of varying combinations of wavelengths showed that irradiation with UV-A, UV-C, or a combination of both is more effective than UV-B irradiation. In addition, the increase in vitamin D in shiitake mushrooms irradiated by UV-C was time-dependent, that is, dose-dependent. Nevertheless, the increase rates decreased with time. The concentration of ergosterol decreased with the increase in vitamin D, but ergosterol was only partially converted to vitamin D, whereas most of the ergosterol was probably UV-degraded. Exposure to ultraviolet light in ethanol suspension offers an effective way to increase the concentration of vitamin D and thus improve the nutritional value of edible mushrooms, as well as make them more functional as a source of vitamin D to improve the consumer health.