Abstract
The utilization of phenolic compounds from wine wastes as source of biologically active compounds has attracted the attention of many researchers with the focus being mostly on grape seeds, grape skins and pomace. Lees is a waste material generated during winemaking which is poorly investigated. Little is known about the effect of the vinification technique on the phenolic compounds and biological activity of wine lees extracts. In this study, Pinot noir (PN) and Riesling (RL) lees from different winemaking techniques were extracted with aqueous ethanol, aqueous methanol or aqueous acetone (1:1 [v/v]), both non-acidified and acidified with 1% HCl, in order to investigate the effect of the solvent extraction system on the recovery of total phenol content (TPC). The extracted materials were characterised for their antioxidant activity [DPPH radicals scavenging and Oxygen Radical Absorbance Capacity (ORAC)] and antimicrobial activity (against Staphylococcus aureus, Escherichia coli and Candida albicans). Furthermore, the effects of oxidation (using horseradish peroxidase and hydrogen peroxide as oxidising model system) on phenolic composition and the biological activity the polyphenols were investigated in (i) a model system composed of catechin and grape seed tannin extracts at various ratios and (ii) in selected wine lees samples (PN and RL).
Extraction with 50% acidified ethanol had the highest TPC and the highest antioxidant activity as determined using ORAC assay. The results demonstrated that acidified solvents can affect the kinetics of the DPPHˑ scavenging activity and that optimal results for that assay were found in pH range of 5 to 7. Vinification techniques including the application of enzymes and the addition of extra tannin can potentially increase the TPC in lees; left whole berries in fermentation limited the extraction of phenolic compounds. The All wine lees had free radical scavenging capacities. All white lees and three red (PN4, PN6 and PN8) extracts exhibited antibacterial effects and the minimum inhibition concentration (MIC) value indicated that the antimicrobial activity of lees extracts were less effective against E. coli compared with the Gram positive S. aureus. Quercetin-methyl-glucoside (QMG) concentration was found to correlate with bactericidal activity found against S. aureus (r = - 0.499; P < 0.05). Oxidation slightly reduced the TPC, TTC and the antioxidant activities (DPPH and ORAC). No significant changes (P > 0.05) were found for the effect of oxidation on antimicrobial (against S. aureus and E. coli) and antifungal activities (C. albicans). Quercetin and QMG was correlated with the inhibition of the growth of C. albicans.
Results from the present study demonstrated that lees extracts have antioxidant and antimicrobial activities but these activities are affected by processing conditions. Oxidation can decrease the antioxidant activity of model lees with higher proportion of catechin, similar trend was also found with wine lees. However, oxidation did not affect the antimicrobial activity. New Zealand wine lees can potentially be an inexpensive source of antioxidant and antimicrobial agents.