Antioxidant and Aromatic Properties of Aqueous Extracts of Pleurotus nebrodensis as Potential Food Ingredients

<i>Pleurotus nebrodensis</i> has raised the interest of the food and nutraceutical industry due to its valuable organoleptic characteristics coupled with antibacterial and antitumor properties. Given this interest, this study aimed to identify effective, cheap, and eco-friendly technologies to prepare extracts able to convey the bioactive compounds while retaining the typical mushroom aroma. Two aqueous extracts were prepared based on a freeze-thaw (FT) and ultrasound-assisted (UA) method. The extracts, both in liquid and lyophilized form, were analyzed by HPLC to determine the phenolic compounds. Moreover, the volatile organic compounds, total phenolics, total flavonoids, total phenolic acids, procyanidins, and ascorbic acid were determined, while the antioxidant activity was assessed by DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS radical scavenging activity, ferric-reducing/antioxidant power (FRAP), and cupric-reducing antioxidant capacity (CUPRAC) assays. The UA extraction showed significantly higher (<i>p</i> < 0.05) phenolics (5.05 vs. 4.02 µg/g DW) and flavonoids (0.74 vs. 0.23 µg/g DW) but lower procyanidins (12.33 vs. 15.93 µg/g DW) and ascorbic acid (6.23 vs. 7.02 µg/g DW) than the FT extracts, resulting in lower antioxidant activity. Among the phenolic constituents, gallic acid was found to be the most abundant in all <i>P. nebrodensis</i> extracts. Regarding aroma, FT more effectively preserved volatile alcohols and aldehydes-particularly 1-octen-3-ol and hexanal-while UA led to greater volatile losses. These results highlight that the extraction method significantly affects both antioxidant composition and volatile integrity, with implications for designing <i>P. nebrodensis</i>-based food ingredients.