Microwave-Assisted Extraction of Pleurotus mushrooms cultivated on wine grape pomace and antioxidant activity evaluation

In accordance with the principles outlined in the National Recovery and Resilience Plan (PNRR), we focused on the concept of sustainable agriculture and circular economy. The primary goal of the project is the eco-sustainable reuse of waste from wineries and vineyards [1], specifically the by-products of cultivating and processing "Nero di Troia" CV grapes supplied by the company "Trulli il Castagno Snc" in Martina Franca (TA) for the purpose of using this waste as a possible growth substrate for producing edible and medicinal mushrooms. The genus Pleurotus (Fr.) P. Kumm. comprises mushrooms that are economically significant, globally cultivated, widely used in human nutrition, and acknowledged for their medicinal properties [2]. Within this genus, P. ostreatus (Jacq.) P. Kumm., Führer Pilzk. and Pleurotus eryngii (DC.) Quél are among the most extensively cultivated and recognized species worldwide. The cultivation process of P. ostreatus and P. eryngii on "Nero di Troia" wine pomace was conducted to evaluate its productive efficiency and qualitative characteristics, with potential for large-scale cultivation of wild mushroom. Two different substrates were used for cultivation of P. ostreatus and P.eryngii: wheat straw, as the control substrate, and wine pomace in a 1:1 ratio by dry weight with wheat straw. P.ostreatus showed a good production performance in comparison with P.eryngii, which presented considerable difficulties in growing on wheat straw. The harvested mushrooms were first dried to a constant weight, pulverised and subjected to Microwave-Assisted Extraction (MAE), a green extraction technique that reduces energy consumption and solvent use compared to conventional methods, aligning with the principles of eco-friendly and sustainable practices. Extractions were conducted at 80 °C for 5 minutes in three different solvents: water, absolute ethanol and ethyl acetate. Spectrometric analyses on the obtained extracts were performed for a comprehensive characterization of the bioactive profile of the mushroom extracts, thus possibly highlighting the impact of wine pomace as a substrate on the chemical composition of the mushrooms. The chemical composition of the ethyl acetate P. ostreatus extract was analyzed by gas chromatography-mass spectrometry (GC-MS) and a higher concentration of ergosterol produced in mushrooms cultivated on wine pomace than in those developed on wheat straw was observed. High-resolution mass spectrometry (HRMS) analysis of the aqueous and ethanolic extracts does not provided comprehensive data. The antioxidant activity of the lyophilized aqueous extracts of P. ostreatus and P. eryngii was also evaluated. The results obtained from Folin-Ciocalteu assay showed higher polyphenol content in POP (P. ostreatus extract cultivated on wheat straw) samples, with values of about 2 g/100g DM. Flavonoid content was not detected in any samples. Antioxidant activity, determined through (DPPH and FRAP assays), was generally lower for PEV (P. eryngii extract cultivated on wine pomace) samples with respect to POP and POV (P. ostreatus extract cultivated on wine pomace), in turn showing almost similar values. In particular, POP2 exhibited the highest FRAP value of about 0.79 g/100g DM. These results, in addition to the cultivation aspect, shed light on wine pomace as mushroom cultivation substrate useful in terms of waste valorization and eco-sustainability.