Comparison of Ergosterol and Vitamin D in Mushrooms and Using Ultraviolet Irradiation Directly on Dry Powder or in Ethanol Suspension.

Vitamin D deficiency is a severe worldwide health issue. Edible mushrooms are an excellent vitamin D source and have gained popularity worldwide as a nutritional food. The objective of this study was to investigate the conversion efficiency of ergosterol to vitamin D in and mushrooms under ultraviolet (UV) irradiation directly through dry powder or in ethanol suspension (1:20 g/mL, solid to liquid ratio). Several parameters of UV irradiation conditions such as the material form (dry powder or dry powder in ethanol suspension), exposure time (30, 60, or 120 min), wavelength type (UV-C, UV-B, or UV-A), wavelength combination (UV-C plus UV-B, UV-C plus UV-A, UV-B plus UV-A, or UV-C plus UV-B plus UV-A), and wavelength sequence (UV-C → UV-B, UV-C → UV-A, UV-B → UV-A, or UV-C → UV-B → UV-A), were optimized. Under the optimal UV irradiation conditions (dry powder in ethanol suspension irradiated with UV-C at 40 cm for 120 min), vitamin D concentrations increased from not detectable to 72 μg/g (dw) in the dry powder and 1104 μg/g (dw) (about 15-fold increase) in the ethanol suspension. After UV irradiation, the vitamin D concentration increased from undetectable to 57 μg/g (dw) in the dry powder. In contrast, UV irradiation increased the concentration to 877 μg/g (dw) (about 15-fold higher) in the ethanol suspension. Comparison of the effect of various wavelength combinations showed that UV-C irradiation is more effective than UV-A or UV-B. Furthermore, when irradiated by UV-C at a 40 cm irradiation distance in the ethanol suspension, the increase in vitamin D in and mushrooms was time- or dose-dependent. The conversion rate of vitamin D was low to undetectable under dry powder irradiation, but its ergosterol loss rate was higher than in ethanol suspension irradiation. The ergosterol loss rate in dry mushrooms was higher than in the dry mushroom powder. Ultraviolet irradiation in ethanol suspension could greatly increase the vitamin D concentration than directly on the dry powder and thus make edible mushrooms more practical as a natural vitamin D source for consumers after entirely removing the ethanol.