Abstract
Analysis of protein precipitable wine tannins has become more commonplace due to the simplicity of the methodology and strong correlations with the sensory perception of astringency. A protein precipitation method adapted for wine is a variant on the Hagerman and Butler method that allows for measure of both tannins and polymeric pigments. The original method used 5% w/v sodium dodecyl sulfate (SDS) and an alkaline buffer (triethanolamine, TEA pH 9.4) to dissolve the tannin-protein precipitate and to support the colorimetric reaction with ferric chloride. However, we found a significant background increase presumably due to the alkaline pH of the resuspension buffer, which is known to oxidize phenolics. We experimented with several buffer formulations and found that pairing urea with TEA instead of SDS allowed lower pH buffer formulations. Using urea TEA at pH 7 and 8 we found significantly lowered background absorbance and significantly less background drift over time as well as a significantly greater amount of tannin recovered, likely the result of less oxidative destruction of the tannins. We also explored the impact of utilizing different buffers on analysis dilution and total iron reactive phenolics and found that utilizing TEA-urea buffers at pH 7 or 8 would be comparable to previous results gathered at pH 9.4 with the TEA-SDS buffer.
- ©2014 by the American Society for Enology and Viticulture
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