Comparative extraction of bioactive compounds from spent mushroom substrates of Lentinula edodes and Pleurotus ostreatus using subcritical water and pressurized ethanol

This study aimed to assess subcritical water extraction (SWE) and pressurized ethanol extraction (PEE) for recovering bioactive compounds from spent mushroom substrate (SMS) derived from shiitake and oyster mushrooms. The extraction of bioactive compounds can facilitate the valorisation of SMS, an increasingly important waste stream whose management and disposal pose challenges for both mushroom producers and the environment. A 32 experimental design, using three temperatures (125, 150, and 175 degrees C) and three holding times (0, 15, and 30 min) was used in SWE. PEE was run at a single temperature (175 degrees C) and two holding times (0 and 15 min). The experimental results revealed that the highest extraction yield was achieved in shiitake SMS using SWE at 175 degrees C and 15 min. In most SWE conditions, shiitake SMS yielded higher concentrations of total phenolic compounds, total carbohydrates, and beta-glucans compared to oyster mushroom SMS. Ascorbic acid, vanillic acid, protocatechuic acid, and gallic acid were the most abundant phenolic acids identified in both extracts. The SWE extracts of shiitake SMS exhibited higher DPPH and FRAP antioxidant activity than those of oyster mushroom SMS, and this activity increased with increasing temperature and time. PEE extracts exhibited higher DPPH and TEAC antioxidant activity for oyster mushroom SMS compared to shiitake SMS and showed a negative trend with increasing extraction time at 175 degrees C for both SMS. Our results show that SWE and PEE are viable methods for extracting bioactive compounds from SMS.