The antioxidant properties of wine lees extracts in model wine

While the ethanol and tartaric acid contained in wine lees are typically recovered by distilleries, the remaining solid fraction (yeast biomass) is usually disposed of, thus negatively affecting the overall sustainability of the wine industry. Previously we demonstrated that the wine lees’ solid fraction could be submitted to a food-grade physical extraction method (autoclave, 20 min, 121°C) to yield yeast polysaccharides with proven foaming, emulsifying and wine stabilizing properties [1,2]. In this study, the autoclave extraction procedure was applied directly on lees from red winemaking. As a result, two extracts were obtained: the Total extract, namely the whole lees after autoclave containing the soluble and insoluble fractions; the Supernatant, containing only the soluble compounds released during extraction. The composition of the extracts in terms of protein, polysaccharides, glutathione, total thiols, and total polyphenol content, was determined by spectrophotometric and chromatographic analytical methods. Subsequently, the extract’s oxidative behavior was tested by dissolving them (0.5 g/L) in model wine (20% EtOH, 5 g/L tartaric acid, 5 mg/L Fe, 0.5 mg/L Cu) containing 30 mg/L free SO2 and 0.5g/L catechin. The O2 and SO2 consumption, color development (as a function of catechin degradation), and linear sweep voltammetry (LSV) behavior were investigated. The effect of the wine lees’ extracts was benchmarked against analogs extracts obtained from a lab-grown culture of the same yeast strain present in the wine lees. Samples prepared with the wine lees’ extracts showed a higher O2 and SO2 consumption rates compared to those prepared with the lab-grown yeast extracts. All extracts protected the catechin from oxidation, with the best protective action achieved by the Total wine lees extract. This extract, along with its analog from the lab-grown yeast culture, showed the greatest resistance to anodic oxidation according to LSV. The protective action on catechin displayed by all the extracts was not fully explainable by their content in antioxidant compounds as glutathione, thiols, and wine polyphenols. Interestingly, the fact that the best results were obtained using the Total extracts in which both the soluble (released polysaccharides) and insoluble (yeast cell walls) fractions were present, allowed to hypothesize that other compounds are involved in limiting the catechin oxidation. In this scenario, the candidates are the yeast membrane sterols as they possess an oxygen-consuming action, and yeast cell wall polysaccharides as they could bind to catechin thus making it unavailable for oxidation. To conclude, wine lees can be considered a novel source of yeast extract with potential oenological application also against quality-affecting oxidative reactions. If adopted on a large scale, this wine lees valorization strategy would result in an improvement of the overall sustainability of the wine industry.