What is the fate of oxygen consumed by red wine? Main processes and reaction products

Oxygen consumed by wine is used to oxidize sulfur dioxide and ethanol to form acetaldehyde wine oxygen consumption rate (OCR) was negatively correlated with the initial acetaldehyde level. Experiences carried out at 25 ºC with red wines have demonstrated that after consuming a large amount of O2, some young wines did not form acetaldehyde. However, acetaldehyde level increased in aged wines. Higher acetaldehyde accumulation in aged wines can be explained by Aldehyde Reactive Polyphenols (ARPs) smaller amounts, because of their lower reactive potential due to high O2 exposure. Models characterized ARPs as anthocyanins, flavonols, tannins and flavanol-anthocyanins adducts. These ARPs should be closely related to wine aging potential by measuring acetaldehyde consumption rate (ACRs) and/or the maxima amounts of acetaldehyde each wine can consume. 

The main goal of this work was to find a new polyphenol index which should be linked to wine oxygen consumption kinetics. It could indicate the maximum oxygen level that a wine can consume. As well as, elucidate if acetaldehyde is the reactive species with ARPs, but one of its radical precursors in the Fenton reaction. 

Three experiments were prepared in anoxia followed by total acetaldehyde determination by using HPLC: 1) wines spiked with 30 and 300 mg/L of acetaldehyde and incubated at 25, 45 and 70 °C; 2)synthetic wines spiked with 15 to 120 mg/L of acetaldehyde and polyphenol extracts; 3) synthetic matrices filled with malvidin-3-O-glucoside, catechin and a mix of both, which were exposed to: a) 8 mg/L O2 to form acetaldehyde in situ or b) to anoxia and spiked acetaldehyde (11 mg/L). 

Several wines consume acetaldehyde at different rates, which are particularly imprecise at low temperatures. This makes impractical the use of ACRs as an index to categorize wine polyphenolic composition by defining a discrete ARP category. ACRs are too complex, showing a high dependence order towards acetaldehyde level and an equilibrium concentration. Such concentrations were found to depend on the previous acetaldehyde uptake by the polyphenolic fraction, but it was too imprecise to take clear conclusions. In any case, measured ACRs are smaller than expected attending to oxygen consumption kinetics and acetaldehyde accumulation rates. No significant differences were found when comparing the acetaldehyde formed in situ or when acetaldehyde was spiked. 

Results show that oxygen consumed by wine is used to oxidize SO2, ethanol and at least 50 % to oxidize ascorbic acid, cysteine, glutathione, H2S, thiols, methionine and phenols. 

This work has been funded by the Spanish Ministry of Economy and Competitiveness (Spanish FPI Program AGL2014-59840-C2-1-R, AGL2017-59840), by Diputación General de Aragón (T53) and Fondo Social Europeo. 

Authors: Almudena Marrufo-Curtido, Elena Bueno-Aventín, Vicente Ferreira, Ana Escudero 

Laboratory for Aroma analysis and Enology (LAAE). Instituto Agroalimentario de Aragón (ia2). Department of Analytical Chemistry. Associated unit to Instituto de Ciencias de la Vid y del Vino (ICVV-CSIC, UR, CAR) Universidad de Zaragoza. 

Email: amarrufo@unizar.es 

Keywords: Oxygen, Acetaldehyde, Polyphenol index, Anthocyanins, flavonols, tannins and flavanol-anthocyanins adducts 

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