Abstract
Pleurotus ostreatus, commonly known as the oyster mushroom, is a widely cultivated edible mushroom characterized by its nutritional value and health benefits. However, its large-scale production generates significant amounts of agro-industrial by-products, such as stipes, residual mycelium, and spent mushroom substrate (SMS). These by-products are often discarded despite their high content of bioactive compounds such as dietary fiber, β-glucans, polyphenols, ergosterol, and essential minerals. This review provides a critical overview of emerging green extraction technologies (i.e., ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), supercritical fluid extraction (SFE), subcritical water extraction (SWE), enzyme-assisted extraction (EAE), and pulsed electric fields (PEF)) as a strategy for the sustainable valorization of bioactive compounds from P. ostreatus by-products. Despite promising results in the extraction of β-glucans and phenolic compounds, industrial scalability remains a challenge due to cost, energy demand, and regulatory issues. In addition, the potential incorporation of these compound by-products into functional food formulations is explored, highlighting their possible applications in meat, bakery, and dairy products. Although notable outcomes have been obtained in the use of the fruiting body as a functional ingredient, further research is needed into the potential use of by-products in order to optimize processing parameters, ensure safety, and validate consumer acceptance. Overall, the sustainable valorization of P. ostreatus by-products represents a dual opportunity to reduce food waste and develop innovative functional ingredients that contribute to health and sustainability.