Studies on the reaction of wine flavonoids with exogenous acetaldehyde

Open Access
- Author:
- Sheridan, Marlena Kenny
- Graduate Program:
- Food Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 03, 2016
- Committee Members:
- Ryan John Elias, Dissertation Advisor/Co-Advisor
Joshua D Lambert, Committee Member
John Coupland, Committee Member
Michela Centinari, Committee Member - Keywords:
- Acetaldehyde
Flavonoid
Anthocyanin
Tannin
Color Stability
Red Wine - Abstract:
- Red wine quality is known to improve with oxidation, typically as a result of exposure to oxygen. These benefits are based on the reaction of acetaldehyde with flavonoids in red wine. Acetaldehyde forms ethylidene bridges between flavonoids resulting in polymeric pigments and modified tannins, contributing to color stability and improved mouthfeel of red wine. Winemakers often use oxygenation techniques in order to take advantage of the benefits of acetaldehyde. These methods are based on the reduction of oxygen in several metal-catalyzed steps resulting in acetaldehyde; undesirable, reactive intermediates are also formed as side products of this mechanism. As these reactive species can result in deleterious effects, oxygen exposure is a relatively risky technique in order to gain the benefits of acetaldehyde. As a replacement for oxygenation techniques, I investigated the use of exogenous acetaldehyde additions to improve the color stability and mouthfeel of red wine. I first determined the viability of exogenous acetaldehyde treatment of a red wine by examining the effects of the treatment during alcoholic fermentation. Two levels of acetaldehyde (100 mg/L and 1000 mg/L) were added to a red wine over eight days of fermentation. After the completion of fermentation, wines were analyzed for their color stability and protein precipitation. High acetaldehyde treatment significantly increased the concentration of polymeric pigments and decreased the amount of protein precipitated by tannin. These results demonstrate the ability of exogenous acetaldehyde treatment to improve color stability and mouthfeel of a red wine. In order to understand the role of wine components in the reaction of acetaldehyde with wine flavonoids, I assessed the effect of pH, dissolved oxygen, and sulfur dioxide (SO2) in model wine solutions. The rate of reaction of acetaldehyde with catechin was significantly increased with lower pH and was not affected by dissolved oxygen. Interestingly, the reaction of acetaldehyde with flavonoids was slowed but not prevented by the addition of SO2 as determined by monitoring the rate of reaction and the formation of polymeric pigments. These results demonstrate that acetaldehyde is reactive, not inert as previously assumed, in its sulfonate form. Based on the efficacy of acetaldehyde in a system with an equimolar concentration of bisulfite in the previous study, I then explored the reactivity of aldehydes from bisulfite adducts. I synthesized α-hydroxyalkylsulfonates from bisulfite and several aldehydes found in wine: formaldehyde, acetaldehyde, propionaldehyde, isobutyraldehyde, and benzaldehyde. The reactivity of aldehydes from their free and bound (sulfonate) forms with catechin was determined. The results demonstrate a clear relationship between reactivity of an aldehyde from its sulfonate and the dissociation constant (Kd) of that sulfonate. The bridged catechin oligomers from these aldehydes were also characterized by MALDI-TOF MS, several for the first time. This work was the first evidence of the reactivity of aldehydes, including acetaldehyde, from their sulfonates. In order to confirm the application of exogenous acetaldehyde in red wine production, I investigated the treatment of red wine with exogenous acetaldehyde, the acetaldehyde-bisulfite adduct, and oxygenation after alcoholic fermentation. A reasonably low concentration of exogenous acetaldehyde (500 μM, 22 mg/L) significantly improved all measures of color stability evaluated, including color density and polymeric pigments. The sulfonate did not have the same effect as acetaldehyde, but did increase several parameters of color stability. The comparison between exogenous acetaldehyde and oxygenation demonstrated the inefficiency of the formation of acetaldehyde from oxygen. While both treatments consumed monomeric anthocyanins, only exogenous acetaldehyde significantly increased the concentration of polymeric pigments. Overall, I demonstrated that exogenous acetaldehyde treatment is a viable alternative to oxygenation for improving the color stability of red wines. At low concentrations (22 mg/L), winemakers could use acetaldehyde to significantly improve color stability and wine quality. Acetaldehyde is also likely to contribute to beneficial reactions of flavonoids in wine when found as a sulfonate, as I showed its reactivity upon the addition of bisulfite and when added as a sulfonate. While further work is needed to optimize its application during red wine production, this work suggests that exogenous acetaldehyde treatment could be an effective method of improving color stability for winemakers.