Tingting Ye, Michael Qian,* Alexander Levin, and Yanping Qian
*Department of Food Science and Technology, Oregon State University, 100 Wiegand Hall, Corvallis, OR, 97331 (michael.qian@oregonstate.edu)

This study investigated the influence of initiated irrigation time on the methoxypyrazine and C13-norisoprenoid compositions of Pinot noir wine. The experiment was conducted in three subregions of the Rogue Valley in southern Oregon for two years, and the Pinot noir vines were irrigated at different irrigation initiation times based on normalized vine water status thresholds (ΔSWP). The ΔSWP was defined as the departure of measured midday stem water potential from the calculated non-water-stressed baseline, varied from 0.2 MPa (control) to the most delayed irrigation (1.0 MPa) in five irrigation initiation times, while the irrigation amount was set at 70% ET_c, based on industry standard. Wines produced in each of the two vintages were analyzed. Methoxypyrazines and C13-norisoprenoids in the wine were analyzed by headspace solid-phase microextraction gas chromatography-mass spectrometry and stable-isotope labeled compounds were used as internal standards for quantification. The results showed that the delayed irrigation initiation time decreased the methoxypyrazine levels and increased C13-norisoprenoid levels in the wines, although the trends depended on vintage and subregion. These changes in volatile composition in response to irrigation initiation timing could affect aroma perception and overall wine quality. Determination of the optimal irrigation initiation timing can provide a guideline for grapegrowers to produce high-quality winegrapes and reserve water resources.

Funding Support: Northwest Center for Small Fruits Research Commission, USDA