Identification of compounds produced by reactions of flavonoids and acetaldehyde in wine

Abstract

During aging, wine consumes small amounts of oxygen. This oxygen intake triggers a series of reactions that lead to flavonoid elongation, which is known to reduce bitterness and astringency while enhancing color stability. The oligomers and polymers formed during aging differ from those produced in the non-aging reactions, as they contain ethylidene-bridges, — a result of acetaldehyde formation, an oxidation product of ethanol [1]. High oxygen ingress can lead to off-flavors, depending on the wine’s stability, with excessive exposure potentially resulting in vinegar formation. Acetaldehyde, a key intermediate in this cascade of reactions, could potentially be added exogenously after fermentation to induce aging qualities without the associated risk of high oxidation. To investigate the effect of this, exogenous acetaldehyde was initially added to model wine (12.5% EtOH, 250 mg/l Catechin, pH 3.5) at 0, 50 and 250 mg/l, at two temperatures (4 and 35 ℃) and with or without SO₂. Samples were collected over 21 days and analyzed using LC-MS/MS, utilizing multiple-reaction-monitoring for ethylidene bridged catechin oligomers. Higher temperature and acetaldehyde concentration accelerated the formation of ethylidene-bridged products. However, sequential acetaldehyde addition did result in a final difference in product formation. Furthermore, the addition of SO₂ as KMBS at 250 mg/l did not completely inhibit elongation but rather slowed the reaction. To further confirm that the observed products were the result of acetaldehyde bridging, acetaldehyde-d₄ was reacted with catechin using the same solution. Ions with an m/z value 4 higher than those in the previous experiment were observed, indicating that acetaldehyde was being consumed in the reaction. Ions resulting from the addition of both acetaldehyde and acetaldehyde-d₄ were identified using a LC-MS metabolomics workflow, demonstrating the formation of multiple products. Combinations of catechin, procyanidin B2, malvidin-3-O-glucoside and acetaldehyde or acetaldehyde-d₄ were reacted in model wine and the predicted ions associated with polymerization via acetaldehyde were detected. Acetaldehyde was also added to Cabernet Sauvignon wine, and MRM methods were used to detect if ions corresponding to ethylidene bridges. Overall, this research could provide winemakers with a new tool for chemically modifying their wines, enhancing desirable aging characteristics while minimizing the risks associated with excessive oxidation.

References

[1] Sheridan, M., Elias, R. (2016). J Agric Food Chem, 64, 45, 8615-8624.