Mapping oxidative evolution of wine polyphenols: impact of medium composition on their oxidative degradation pathways

Abstract

Wine matrix is a complex and continuously evolving medium. The impact of oxygen in wine evolution is a vital factor that critically affects key organoleptic properties such as color or astringency. Moreover, the rising demand for low-alcohol and dealcoholized wines poses an additional challenge due to their heightened susceptibility to oxidation. This work studied the different oxidative pathways of polyphenols and the impact of ethanol on their oxidation. Given that wine characteristics are directly linked to polyphenol evolution, characterizing the different routes that polyphenols can undergo when exposed to oxygenation can provide a deeper understanding of oxygen management within the new trends in winemaking. For this purpose, different solutions containing anthocyanins, flavan-3-ols and/or phenolic acids were prepared to mimic wine-like conditions (5 g/L tartaric acid, 4 mg/L FeCl₃, 0.4 mg/L CuSO₄; pH = 3.6), varying ethanol percentage (0 – 13 %), and polyphenol content and profile. Then, they were subjected to periodic oxygenation ensuring oxygen saturation with an optical oxygen probe. The evolution of phenolic compounds and the formation of degradation products were monitored over two months by means of HPLC-DAD-MS. For each family of compounds, different transformation pathways were identified. On the one hand, polymerization occurred in both anthocyanins and flavan-3-ols, with the formation of polymeric pigments or flavanols with higher polymerization degree (including A-type dimers). On the other hand, all compounds underwent oxidative degradation, especially in the absence of ethanol, identifying quinone species as well as degradation products such as hydroxybenzoic acids and aldehydes, catechol derivatives and chalcones. Furthermore, oxidation-related pigments appeared in the oxygenated solutions containing anthocyanins (vitisins, direct and acetaldehyde-mediated condensates in the presence of ethanol) and flavanols (xanthylium cations and related compounds). Overall, the results show that matrix composition, particularly ethanol content and phenolic profile, fundamentally dictates the oxidative evolutionary pathways of the compounds. Thus, the characterization of these oxidation-derived species could serve as a valuable tool to monitor oxidation in different wine matrices, from traditional white, red or rosé wines to the emerging category of low alcohol or dealcoholized wines.

References

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