Agri-food wastes as substrates for oyster mushroom (Pleurotus ostreatus) cultivation and their agricultural potential.

Fungi of the Pleurotus genus, are known for their health-promoting properties. They are grown on a wide range of lignocellulosic substrates, including i.e. straw, rice hulls and corn residues. There are numerous literature reports proving that the composition of the culture substrate affects the growth rate and yield of oyster mushrooms. The aim of the present study was to optimize the mixture of the culture medium, composed of agro-industrial waste, for the cultivation of Pleurotus ostreatus in order to achieve maximum yield and the fastest mycelial growth. In addition, the chemical composition of selected wastes was determined and the possibility of using spent P. ostreatus substrate as a biostimulant for plant growth was assessed. The best results in terms of yield, mycelial growth rate, and time required for substrate colonization, primordia formation, and first harvest, were obtained for straw with spent brewery grains and for straw with wheat bran in a proportion of 70/30%, while the mixture of wheat straw, wheat bran and sugar beet pulp in a proportion of 50/25/25% gave slightly poorer results. The maximum yield of 51.7 g/bag and the fastest growth was obtained for the substrate with the addition of spent brewery grains. Substrate formula 70% wheat straw, with 30% addition of spent brewery grains, gave the fastest time for substrate colonization, primordia formation and the first harvest (16 days, 20 days, 28 days respectively). The study carried out by ICP-Spectrometry technique confirmed that the Pleurotus spent substrate is a source of valuable elements (Ca, Cu, Fe, K, P, Mg, Mn, S), indicating its biostimulatory potential in agriculture. Enzyme activity associated with substrate (carbohydrate) degradation, performed using a commercial API ZYM assay increased significantly in straw with spent brewery grains and straw with wheat bran mixture. The highest total levels of degradation products were examined by photometric method using commercially available Hach Lange cuvette tests. The highest total content of Pleurotus substrate degradation products, including organic acids, orthophosphate, ammonia nitrogen, nitrate, and nitrite, was found in the substrate supplemented with brewery grains. Their levels increased significantly compared to the control, indicating enhanced degradation activity in this substrate. Substrate after cultivation of higher fungi (Spent Mushroom Substrate-SMS) contains large amounts of valuable elements and can affect the growth and yield of crops. Their amount varies depending on the substrate used and depends on the availability of sources of C and N. Studies of the growth rate of P. ostreatus on a wide range of lignocellulosic substrates, i.e. straw, corn residues, rice husks, among others, are known. The authors of the present study extended these studies to evaluate the biodegradation of waste materials that have not yet been used in the culture of higher fungi (brewery spent grain, wheat bran, beet pulp), making a significant contribution to the discipline. This study supports the implementation of the Sustainable Development Goals, by promoting the valorization of agro-industrial waste through sustainable biotechnological processes.