Dynamics of sterols and fatty acids during UV-B treatment of oyster mushroom

•UV-B treated oyster mushrooms accumulated >100μg of vitamin D2g−1 dry matter.•Photoproducts lumisterol2, tachysterol2 and previtamin D2 increased concurrently.•Likewise, vitamin D4 accumulated instantly and reached saturation after 1h.•Illumination did not significantly alter the concentrations of fatty acids.•UV-B pretreated oyster mushrooms are a rich source of vitamins D. Fruiting bodies of the oyster mushroom Pleurotus ostreatus were illuminated with UV-B with a light intensity maximum at 310–320nm and 11.5W/m2 for 60min at 20°C. Changes of the sterol and fatty acid spectrum were quantified. The onset of ergocalciferol (vitamin D2) formation was immediate in fruiting bodies illuminated from the lamella side, in sliced fruiting bodies, and in the stipes. Saturation concentrations above 100μg/g of dry matter were reached after 1h. At the same time, the concentrations of the photo-isomers lumisterol2, tachysterol2 and previtamin D2 increased in this order. 22-Dihydroergocalciferol (vitamin D4), showed the same course of increase and reached a maximum concentration of around 20μg/g dry matter. With the exception of linoleic acid in cut fruiting bodies, fatty acid concentrations remained almost constant. One serving of UV-B pretreated sliced oyster mushroom covered the weekly demand of vitamin D of an adult.