Submitted to: Northwest Center for Small Fruit Research Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 29, 2010
Publication Date: December 15, 2010
Citation: Lee, J., Tarara, J.M. 2010. Understanding Micro-Oxygenation Techniques and the Oxidation of Grape/Wine Polyphenolics: Final Report. Northwest Center for Small Fruit Research Proceedings. Interpretive Summary: Wine tannins and color are important red wine quality factors that can be manipulated by grape growing and winemaking practices. Tannin quality in wine is a high-interest research topic. Tannins stabilize wine color, enhance mouth-feel, and can impart characteristics that heighten the quality perception of red wines. This study examined the degradation of grape skin and grape seed tannin oxidation. This is the final report for this funded study.
Technical Abstract: Catechin (monomer), purified grape skin proanthocyanidin (polymer), and purified grape seed proanthocyanidin (polymer) underwent monitored accelerated oxidation under continuous oxygenation and UV light, at a constant 20 °C. Compounds were dissolved in model wine solutions with (and without) catechol. Solutions were examined and then contrasted by absorbance measurements, phloroglucinolysis, and subsequent HPLC analysis. Oxidation of these monomers and polymers revealed significant color changes (measureable increase in color density). The presence of catechol increased the half-life of catechin, but the opposite was observed for total skin and seed proanthocyanidins. Skin and seed proanthocyanidin degradation half-life decreased with the addition of catechol. In general, based on second order rate reactions, total subunits of seed proanthocyanidin solutions degraded faster than that of skin proanthocyanidin solutions. As expected, there were decreases of measureable phenolics in both monomer and polymer solutions. Under the study conditions, flavanol monomer and polymer oxidation was chiefly dependant upon initial solution concentration.