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United States Department of Agriculture

Agricultural Research Service


Location: Horticultural Crops Research

2009 Annual Report

1a. Objectives (from AD-416)
Identify and evaluate vineyard practices within the Pacific Northwest that produce high quality fruit and fruit products.

1b. Approach (from AD-416)
Both parties will examine vine characteristics and major chemical components responsible for any differences, or similarities, between differing vineyard practices. We will use simple spectrophotometric methods in addition to more complex analytical methods (HPLC), to better understand qualitative and quantitative effects on grape phytonutrients. Formerly 5358-21000-034-33S (12/2008).

3. Progress Report
Understanding polyphenolic evolution. This study was initiated to better understand the evolution of polyphenolics (focus being proanthocyanidins, also known as tannins). Wine phenolics (tannins, anthocyanins, etc) are crucial factors of red wine that can be altered by grape growing conditions and winemaking practices. Proanthocyanidins play important roles in red wine by stabilizing color and enhancing mouth-feel, which are critiqued qualities of premium wines. By studying the changes that purified compounds undergo in a controlled system (i.e. model wine system, gas doses, etc), it is easier to identify and monitor their progression during winemaking. Controlled oxidation (by continuous oxygenation and UV light) of catechin, purified grape skin proanthocyanidin, and purified grape seed proanthocyanidin that had been dissolved in model wine solutions were compared and monitored. The presence of catechol increased the half-life of catechin (monomer), but the opposite was observed in both skin and seed proanthocyanidins (polymers). All monomer and polymer oxidations were dependant on initial solution concentration. As expected, monomer and polymer solutions showed a decrease in measureable phenolics. The better we understand how grape growing conditions and winemaking practices alter phenolics, the better the industry will be able to improve their production and / or processing techniques to make superior end products. Skin and seed proanthocyanidins were purified in-house from ‘Pinot noir’ grapes obtained at optimum proanthocyanidin extraction maturity. All phenolic solutions (a total of six combinations; catechin, catechin + catechol, skin proanthocyanidin, skin proanthocyanidin + catechol, seed proanthocyanidin, and seed proanthocyanidin + catechol) were oxidized in the phytochemical reaction assembly under continuous oxygenation (oxygen bubbled through a solution of model wine) and UV light. Reaction mixtures were maintained at 20 °C. Samples were drawn at eight time intervals (0, 240, 480, 960, 1920, 3840, 7680, and 15360 sec). Absorbances of the solutions were measured. Drawn samples also underwent phloroglucinolysis subsequently analyzed by HPLC. Methods of ADODR monitoring included e-mail, meetings, and phone calls.

4. Accomplishments

Last Modified: 06/25/2017
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