Enrichment of vitamin D2 in mycelium from submerged cultures of the agaric mushroom Pleurotus sapidus.

Ergosterol, a precursor of vitamin D2, is present in the cell membrane of all fungi. It can be transformed into vitamin D2 by UV-B exposure. In this study, a basidiomycete, Pleurotus sapidus, cultivated in liquid malt extract medium was exposed to UV-B light. In addition, autoclaved, abiotic mycelium was put through UV-B exposure for the first time. The effects of different UV-B exposure times, surface areas and temperatures on vitamin D2 formation were analyzed. The conversion of ergosterol to vitamin D2 at ambient temperature almost reached completion within 10 min resulting in vitamin D2 concentrations of 365 µg (g dry matter)-1. Prolonged exposure of the biotic mycelium for up to 60 min resulted in a reduced vitamin D2 concentration with stagnation at about 280 µg (g dry matter)-1. Exposure of the abiotic mycelium showed a slower increase but also leveled off at the same concentration. Furthermore, it could be shown that vitamin D2 formation depends on the temperature and the exposed surface area. The vitamin D2 concentration augmented after increasing the exposed surface from 65.0 to 298.6 cm2. The ergosterol content of P. sapidus was analyzed in a way similar to vitamin D2 and resulted in 3.75 ± 0.06 mg (g dry matter)-1 ergosterol.