Pressurized liquid extraction of bioactive compounds from Pleurotus ostreatus and Lentinula edodes spent mushroom substrate

Abstract

The global mushroom production is continuously increasing, thanks to mushrooms being a popular low-emission, high-protein and health-promoting food. This results in the mushroom industry yearly giving rise to an abundant amount of spent mushroom substrate (SMS). In reaching the aim of a circular economy, the valorisation of SMS is essential in order to achieve a sustainable bioeconomy. The extraction of bioactive compounds stands out as a prospective application. Due to the compounds resulting from fungal decomposition of lignocellulose in the substrate and the presence of mycelium, SMS contains bioactive compounds. This study aims to investigate the extraction of bioactive compounds from the SMS of oyster mushroom (Pleurotus ostreatus) and shiitake (Lentinula edodes) by applying pressurized liquid extraction. The antioxidant activity of the bioactive compounds and their correlation with individual phenolic acids is another important objective of this study. A 32 factorial design was employed using subcritical water extraction (SWE) at temperatures ranging from 125 °C to 175 °C and holding times of 0, 15, and 30 minutes. Pressurized ethanol extraction (PEE) using aqueous ethanol as solvent was also performed at 175 °C for 0 and 15 min. The concentrations of total phenolic compounds were higher in the PEE extracts than in the SWE ones across the same conditions. The most abundant phenolic acids identified were vanillic acid, ascorbic acid, gallic acid and protocatechuic. The SWE extracts of shiitake SMS showed higher antioxidant activity than those of oyster mushroom SMS, while an opposite trend was observed in PEE extracts. Overall, the PEE extracts showed higher antioxidant activity than the SWE extracts across similar conditions for both SMS. A strong correlation was found between the concentration of total phenolic compounds in the extracts and the antioxidant activity. Among all identified phenolic acids, ferulic and chlorogenic acids showed correlations with FRAP capacity even though they were identified in lower amounts. This suggests that, phenolic acids could be important contributor for antioxidant activity of the SMS extracts. In addition to total phenolic compounds, polysaccharides could potentially be another contributor for the observed antioxidant activity. As phenolic compounds and carbohydrates are effectively recovered in this study, SWE and PEE could be viable methods for extracting bioactive compounds from SMS of shiitake and oyster mushroom