Conversion of ergosterol into vitamin D2 and other photoisomers in Agaricus bisporus mushrooms under UV-C irradiation

Agaricus bisporus mushrooms contain high levels of ergosterol (3–8 mg/g dw), which can be converted into vitamin D2 (VD2) under ultraviolet irradiation (UV). However, the photoconversion of ergosterol can also lead to the production of inactive photoisomers decreasing the production yield of VD2. This study assesses the impact of UV irradiation conditions on the conversion of ergosterol into vitamin D2. The effects of various parameters were tested including the mushroom form (powder, extract, suspension), irradiation time (0–240 min), temperature (20–40◦C), intensity (0.16–0.48 mW/cm2), and agitation during UV-C irradiation. The mushroom extract was the most suitable mushroom form for VD2 production. Beyond VD2, other photoisomers (tachysterol and lumisterol), were detected through HPLC-APCI-MS and their levels increased with deep and prolonged irradiation. The highest VD2 levels (0.95–1.03 mg/g dw) were obtained by irradiating mushroom extracts with an intensity of 0.31 mW/cm2 for 10 min. These results highlight the potential of mushrooms for VD2 production through UV-C irradiation, which is accompanied by the formation of biologically-active photo-isomers.