Volatile composition of Pinot Noir grapes and wines under different viticultural practices in western Oregon Public Deposited



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  • High vegetative growth of Pinot Noir vine is a common problem in most vineyards of Oregon's Willamette Valley, where sunlight exposure and heat accumulation are limited. Consequently, growers in this region commonly use vineyard management strategies to regulate vine vigor and improve grape and wine quality. Wine quality is greatly correlated with grape volatile composition. However, no study has been done to fulfill the knowledge gap of how specific viticultural practice affect Oregon Pinot Noir grape and wine volatile composition. Accordingly, three studies were conducted to evaluate impacts of viticultural practices (i.e., cover crop, leaf removal, and crop thinning) on the volatile composition of Pinot Noir grape and wine in the Willamette Valley of Oregon. Pinot Noir grape chemical and volatile composition was investigated over three growing seasons (2008, 2009, and 2010) in a commercial vineyard where vines were managed using three vineyard floor management practices. The vineyard floor practices included different inter-row management: permanent grass (Festuca rubra spp. rubra) cover (Grass), alternating grass cover and tillage (Alternate), and tillage of every alleyway (Tilled). Fruit chemical and volatile compositions were analyzed by High Performance Liquid Chromatography (HPLC) and Stir Bar Sorptive Extraction-Gas Chromatography-Mass Spectrometry (SBSE-GC-MS). Results showed that different vineyard floor practices did not affect the grape general ripeness in most of years (2008 and 2009), but in 2010, Grass treatment caused decreases levels of sugar and organic acids in grapes. In addition, Grass treatment reduced levels of berry free amino acids but increased levels of quercetin glycosides and anthocyanins. Compositions of grape volatile and their precursors were also affected by treatments. Grass treatment increased free-form terpenoids and decreased free-form C₆ compounds (hexanal, trans-2-hexenal and 1-hexanol) and β-damascenone in most of the years. There was a negative correlation between vine pruning weight and levels of free-form terpenoids, while, a positive correlation between vine pruning weight and free-form C₆ compounds and β-damascenone. Furthermore, Alternate treatment had the highest concentrations of bound-form terpenoids. Wines were made when grapes reached commercial maturity and wine compositions were analyzed using HPLC, GC-FID and GC-MS. Results showed that the wine made from grapes with vineyard floor management treatments Alternate and Grass had higher levels of anthocyanins compared to Tilled treatment. Wine volatile composition was affected by treatments as well but in different ways. Cover crop treatments increased levels of branched-chain esters, acetates, terpenoids, and phenethyl alcohol in wine; meanwhile, they decreased levels of straight-chain ethyl esters, higher alcohols (1-propanol, isobutyl alcohol, and isoamyl alcohols), β-damascenone, ethyl vanillate, dimethyl sulfite and methanethiol. A second study was conducted to further investigate the impact of fruit-zone leaf removal practice on Pinot Noir grape and wine volatile composition over three growing seasons (2010, 2011, and 2012). Grapevines were managed to have four different leaf removal treatments, including removing 0% (None), 50% and 100% of leaves from the cluster zone at berry pea-size stage, and a current local industry standard treatment (IS). Results revealed that leaf removal practice did not alter vine growth or berry ripening, but increased levels of quercetin glycosides and anthocyanins in grapes. Moreover, leaf removal increased both free- and bound-form volatile compounds in grapes. The 100% leaf removal increased levels of terpenoids (bound-form) and β-damascenone (free- and bound-form) compared to control. In addition, levels of terpenoids and β-damascenone were positively correlated with sunlight exposure. Meanwhile, Pinot Noir wine quality was enhanced by leaf removal. The 100% Leaf removal treatment had higher levels of anthocyanins and volatile compounds, such as linalool, a-terpineol, β-damascenone and several esters (e.g., ethyl butanoate, ethyl octanoate, methyl vanillate, and ethyl vanillate) in final wine. Analyses of potential volatile compounds following acid hydrolysis of wine showed that 100% leaf removal increased levels of bound-form C13-norisoprenoids (e.g., β-damascenone, vitispirane and TDN). The third study was conducted to investigate the impact of crop thinning on volatile composition of Pinot Noir grape and wine with focus on the severity and timing of crop thinning. Crop levels were moderately (35% crop removed) or severely (65% crop removed) thinned at pre-bloom, fruit set, lag phase, or véraison, with no crop thinning as the control treatment. Our data indicate that crop thinning had limited impact on grape and wine volatile compositions with high variation over three seasons (2010, 2011 and 2012).
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