Mushrooms grown in the wild are non-commercially viable due to low volume and environmental contamination. Therefore, PSK is now produced commercially from cultured mushrooms or mycelia cultivated on solid substrate68 or mycelial biomass produced in submerged fermentation68-70.
The culture medium contains glucose or sucrose as the carbon source and peptone, yeast extract, yeast powder, soybean meal and soy sauce as a source of nitrogen, magnesium and phosphate. Fermentations are carried out for 7 days at 23-280C with stepwise feeding with fresh medium.
The yield obtained as a biomass varies from 4 to 23 g/L depending on the size of the fermentor or the bioreactor. PSK is obtained by a multi-step hot water extraction of the Coriolus versicolor hyphae biomass. The extract is concentrated and the active substance is recovered by precipitation with ethanol.