Enhancement of bioconversion efficiency and chemistry of the mushroom, Pleurotus sajor-caju (Berk and Br.) Sacc. produced on spent rice straw substrate, supplemented with oil seed cakes

The effect of supplementing the spent rice straw substrate, selected at two different levels of bioconversion efficiency (BCE), 8 and 12%, of Pleurotus sajor-caju, with extra organic nitrogen (in the form of oil seed cakes) was studied on further production of mushrooms, their chemistry and the increase in the in vitro dry matter digestibility (IVDMD) of rice straw. The spent rice straw was supplemented with the oil seed cake powders in amounts equivalent to 0.15–0.60% of nitrogen present in the undegraded rice straw, that is used for mushroom culturing. The cotton seed powder proved to be better in enhancing the mushroom yields (up to 12 times those of the unsupplemented spent straw), than the other oil seed cakes such as mustard, niger, soyabean and sunflower. Chemically, the cottonseed powder supplemented mushrooms showed increased protein, fat and decreased carbohydrate contents. Also, there was a significant reduction in the spawnrun period, compared to the unsupplemented rice straw. A considerable increase in the IVDMD of the supplemented spent straw was observed as compared to the IVDMD of the unsupplemented spent straw. Due to cotton seed cake supplementation, there was about a 27% increase in the IVDMD value of the spent straw that resulted in 8% BCE. The mushrooms produced on the spent rice straw substrate, with supplementation of cottonseed powder, did not contain any residues of gossypol, and accordingly, they can be a valuable food or feed.