Unconventional chitosan from mushroom by-products as an alternative fining agent for white wines stabilization

Protein haze in white wines, conventionally managed with bentonite, poses significant drawbacks. Since bentonite fining is associated with wine losses, colour and aroma depletion, and environmental concerns, sustainable alternative are needed. This study investigated a novel and unconventional chitosan, sustainably extracted from mushroom ( Pleurotus ostreatus ) by-products using an environmentally friendly subcritical water process, as a fining agent. Chitosan was applied at 20, 60, and 100 g/hL to three unstable white wines (Graševina, Malvasia, and Traminer) to evaluate its impact on protein stability, phenolic composition, and aroma profile. The treatment significantly reduced protein instability (up to 44% in Graševina) and Pathogenesis-Related (PR) protein levels (up to 51% in Malvasia), also suggesting a variety-specific efficacy. The addition of chitosan did not significantly alter the polyphenols content or wine color and even increased an oxidizability index at the highest dosage, suggesting a preservation of wine phenolics. A dosage-dependent decrease in ester concentrations (up to 26% at 100 g/hL) was detected, while levels of alcohols, fatty acids, and varietal aroma compounds remained largely unaffected, at least above sensory thresholds, indicating a minimal impact on the wine aromatic profile. Overall, this unconventional, by-product derived chitosan offers a sustainable and promising solution for the winemaking sector, enhancing circular bioeconomy strategies.