Ezekiel R. Warren, Misha T. Kwasniewski,* and Ryan J. Elias
*The Pennsylvania State University, Rodney A. Erickson Food Science Building, State College, PA, 16803 (mtk5407@psu.edu)

Small amounts of oxygen are consumed during red wine aging, causing a cascade of reactions resulting in polyphenol elongation. The actual elongation is induced by acetaldehyde, an oxidation product of ethanol, creating ethylidene bridges between polyphenols. Elongation decreases bitterness and astringency while increasing color stability. Natural ingress of O₂ can cause other unwanted reactions and off-flavors depending on the stability of the wine and, in extreme cases, may even facilitate the growth of Acetobacter sp. It has been previously demonstrated that the direct addition of acetaldehyde can be added postfermentation to induce elongation, while avoiding excess dissolved O₂. To further study this reaction and the products produced, exogenous acetaldehyde was 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°C) with and without SO₂. Solutions were sampled over 21 days, monitored using a liquid chromatography with tandem mass spectrometry (LC-MS/MS)-based method developed with multiple-reaction monitoring for ethylidene bridged catechins. Increasing temperature and acetaldehyde concentration increased the rate at which products were formed. Sequential addition of acetaldehyde instead of one large addition did not result in an ultimate difference in elongation products. Additionally, the addition of SO₂ at 250 mg/L did not fully inhibit elongation, indicating this reaction can proceed even in the presence of free SO₂, though at a decreased rate. To further characterize products formed, isotopically labeled acetaldehyde-d4 was reacted with catechin. Using a metabolomics workflow, ions produced from adding acetaldehyde and acetaldehyde-d4 were identified, showing the production of many more products than had been identified previously. Further investigations of this type were conducted with a mixture of catechin, procyanidin B2, and malvidin-3-O-glucoside. Acetaldehyde was added to Cabernet Sauvignon wine and the same ions were observed through LC-MS/MS. Ultimately, this research could give a new tool for winemakers to enhance their wine.

Funding Support: Pennsylvania Liquor Control Board