Oyster mushroom (Pleurotus ostreatus) is a good source of bioactive compounds that have numerous health
benefits and medicinal properties. In this study, the effect of P. ostreatus cultivation in agro-waste substrates on its
potential as a food additive with antioxidant and antimicrobial activities was investigated. Extracts of P. ostreatus cultivated
on mixed rice and wheat straws (RS+WS) substrates showed higher total polyphenols (TPC), total flavonoids
(TFC),α-tocopherol content, ferric reducing antioxidant power and antibacterial activities than those cultivated on rice
straw (RS) alone. The HPLC analysis of their ethanolic extracts revealed 11 phenolic compounds including p-hydroxy
benzoic acid, naringenin, kaempferol and apigenin as major compounds. The aqueous and ethanolic extracts of both
cultivates showed significant antibacterial activity against Salmonella typhimurium, Escherichia coli, and Staphylococcus
aureus, while no inhibitory effect on Bacillus cereus was observed. The results indicated that P. ostreatus
cultivation is an effective bioconversion process that is capable to transfer agro-wastes into potentially valuable source
of natural antioxidant and antimicrobial additives for further use in functional food products.