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The polyphenolic content and antioxidant capacity of wine has well been studied in the literature, and is a topic often discussed on this blog. It has been studied so much that we’re all aware of the fact that these characteristics vary significantly from wine to wine, depending upon many factors including but not limited to grape variety, aging time (as well as how the wine is aged), and environmental conditions. According to many studies, there is a trend of increasing concentrations of polyphenolic compounds in wine as the wine is aged for longer periods of time, though this can vary again based on the aforementioned outside forces.
The study presented today is a short one (phew, right?), examined the evolutionof polyphenol content, antioxidant content, and color in old Sherry wines. The authors also sought to determine if antioxidant activity is correlated with the age of the wine.
26 Sherry wines from vintages between 1935 and 1996 were analyzed. All wines were oloroso Sherries which were made in the oxidative method (i.e. no secondary fermentation with flor yeasts). All wines were made with the white Palomino Fino grape variety and were aged in American oak barrels. For each wine, the following were measured and analyzed: total polyphenol content, individual polyphenols, antioxidant activity, and color.
• Concentrations of all parameters measured trended higher in those Sherry wines that were aged for longer in oak barrels than those aged for shorter periods of time.
• For those Sherry wines aged for longer periods of time in oak barrels, the following compounds were most prominent: hydroxymethylfurfural, furfural, protocatechuic acid, tyrosol, p-coumaric acid, and syringaldehyde.
• The highest levels of polyphenols were found in those wines aged for longer in oak barrels than those aged for shorter times.
• The oldest Sherry wines (as old as 1935) had extremely high levels of antioxidant activities.
o The authors attributed the high antioxidant levels to the aging in oak barrels, since the grapes used to create these Sherries were white grapes, and white grapes do not have very high levels of antioxidants to begin with.
• Based on the aforementioned results, the authors claim that the level of antioxidant activity is “clearly related” to the length of time the Sherry wine is aged in oak barrels.
• A strong influence of polyphenols on the antioxidant activity of the Sherry wines was found.
o Those polyphenols most highly correlated with the antioxidant activity in the Sherry wines were: protocatechuic acid, protocatechuic aldehyde, syringic acid, vanillin, and p-coumaric acid.
• SO2 levels for the Sherry wines tested were found to be between 8 and 17mg/L which correlated with the antioxidant activities of the wines, but was not statistically significant.
• Those Sherry wines that were aged in oak barrels for longer periods of time were darker in color than wines aged for not as long.
• The above relationships were all confirmed with principle components analysis and linear discriminating analysis.
This study was mostly “for the sake of science”, though could potentially have interesting applications in the real world. The study found that those Sherry wines aged in oak barrels for longer periods of time possessed greater levels of polyphenols and antioxidant activities (as well as darker colors). If you’re looking to maximize your polyphenol and antioxidant activity intake, then based on this study you know to go for wines aged for longer periods of time in oak barrels.
One thing I was wondering while reading this article was whether or not this type of analysis could be used for determining authenticity of wines suspected of possible fraud. I suppose the technique itself isn’t that sensitive, but it potentially be used in concert with other techniques. For example, if the aging treatment was known for the particular wine in question, then one might be able to measure the polyphenol levels and antioxidant activity to get a ballpark idea of whether or not the wine could be legit or if it could be a fraud.
If it was known that the wine was aged for a long period of time in oak barrels yet the polyphenol levels and antioxidant activities were extremely low, then red flags could be raised on the authenticity of the wine. I suspect this technique would not be very sensitive, and could thereby require other techniques to beperformed if the results were not clear, but I think it could be a quick a dirty test if no other options were immediately available. Of course, less invasive methods for determining the authenticity of wines are currently in development, so this technique may not be the best option for multiple reasons, but hey, I’m just thinking out loud here!
Can you think of other applications for this information about polyphenol levels and antioxidant activities in Sherry wines? Please feel free to leave your comments!
Source: Schwarz, M., Carmen Rodríguez, M., Guillén, D., and Barroso, C.G. 2012. Evolution of the colour, antioxidant activity and polyphenols in unusually aged Sherry wines. Food Chemistry 133: 271-276.