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

Ergosterol, a precursor of vitamin D-2, is present in the cell membrane of all fungi. It can be transformed into vitamin D-2 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 D-2 formation were analyzed. The conversion of ergosterol to vitamin D-2 at ambient temperature almost reached completion within 10 min resulting in vitamin D-2 concentrations of 365 A mu g (g dry matter)(-1). Prolonged exposure of the biotic mycelium for up to 60 min resulted in a reduced vitamin D-2 concentration with stagnation at about 280 A mu g (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 D-2 formation depends on the temperature and the exposed surface area. The vitamin D-2 concentration augmented after increasing the exposed surface from 65.0 to 298.6 cm(2). The ergosterol content of P. sapidus was analyzed in a way similar to vitamin D-2 and resulted in 3.75 +/- 0.06 mg (g dry matter)(-1) ergosterol.