Effects Of Viticultural Practices And Botrytis Infection On Aroma Composition Of Grape And Wine

Aroma compounds play an important role in the quality of wine. Viticultural practicesby controlling water supply, sunlight exposure or disease were used to improve the quality ofgrape, and subsequently the wine. In this study, the effect of deficit irrigation, grape berrysunlight exposure, grapevine vigor variation, and the influence of grape berry Botrytis cinereainfection on volatile compounds of grape and wine were evaluated. Aroma compounds wereanalyzed by stir bar sorptive extraction-gas chromatography-mass spectrometry（SBSE-GC-MS）. The major results were summarized as follows:1A SBSE-GC-MS detection method was developed to quantify free and bound aromacompounds in grape berries. Aroma compounds were extracted with citric acid buffer fromgrape berries, blended under liquid nitrogen, and the extracts were centrifuged and filtered.Free aroma compounds were determined directly by SBSE-GC-MS. Bound aromacompouonds were isolated with C18cartridges, and the resulting glycoside extracts wereenzymatically hydrolyzed. The released aglycons were determined by SBSE-GC-MS. Thevalidation results （correlation coefficient, recovery and repeatability） showed that this methodwas simple, fast, and could be used to accurately analyze most of aroma compounds in grapeberries. Free aroma compounds in Merlot and Pinot Noir grape berries, including fatty acidderivatives, terpenes and C₁₃-norisoprenoids were detected, while bound aroma compounds,classified into alcohols, terpenoids, C₁₃-norisoprenoids, benzene derivatives, were determined.In general, the concentrations of free aroma compounds were lower than those of theircorresponding bound aroma compounds.2The SBSE-GC-MS detection technique for analyzing aroma compounds in wine wasvalidated. A10mL wine sample was diluted with10mL salt water, and volatile compoundswere extracted by stir bar at1000r/min for3h. The validation results indicated that thismethod was fast, sensitive and accurate. The aroma compounds including esters, alcohols,fatty acids, terpenoids and C₁₃-norisoprenoids were determined in wines from Pinot Noirclones and concentration differences of aroma compounds in the Pinot Noir wines wereobserved.3The effect of deficit irrigation and kaolin particle film on aroma compounds inMerlot grape berries was investigated. Merlot grapevines were provided with100,70, or35%of estimated crop evapotranspiration （ETc） or35%ETcuntil veraison followed by70%ETcuntil harvest throughout berry development, and particle film （PF） was applied to half vinesin each irrigation main plot in2007and2008. The results indicated that the concentrations of free C6compounds （hexanal, trans-2-hexenal, and1-hexanol） in Merlot grapes decreased,and bound terpene alcohols （nerol and geraniol） and C₁₃-norisoprenoids （β-damascenone,3-hydroxy-β-damascenone,1,1,6-trimethyl-1,2-dihydronaphthalene, and3-oxo-α-ionol）increased in the berries each year in response to severity of vine water stress. Particle filmapplication had minimum effect on free and bound volatile composition in the grapes, andthere was no interactive effect between particle film and deficit irrigation. The concentrationsof bound nerol, geraniol and β-damascenone in grapes were positively correlated with theirconcentrations in wines, suggesting that water deficit could potentially contribute to Merlotwine aroma through influencing grape varietal aroma.4The effect of Pinot Noir grape berry sunlight exposure on volatile compounds of theresulting wine was studied, as well as the role of ultraviolet radiation. Pinot Noir grapevineswere subjected to sunlight exposure treatment conducted by basal leaf removal at the earlydays of veraison with cluster-shading treatment as control. UV radiation treatment wasconducted using filter to transmit natural UV radiation with UV exclusion treatment ascontrol. The results showed that most of esters were not affected by sunlight exposuretreatment, while sunlight exposure treatment resulted in significantly higher concentrations ofterpenoids including citronellol, nerol and geraniol, caused a decrease in the contents of fattyacids （octanoic acid, nonanoic acid and decanoic acid） and an increase in the level ofβ-ionone, as compared to bunch shading treatment. UV radiation exclusion treatmentsindicated that UV radiaton during grape ripening plays an important role in modifying thelevels of some volatile compounds including fatty acids, terpenes and esters in Pinot Noirwines. However, UV radiation had no effect on the levels of C₁₃-norisoprenoids, whichcontradicted the previous hypothesis.5The influence of spatial variation of vine vigor on aroma compounds of the resultingwines was investigated. Four vine vigor zones including ultra low vigor, low vigor, moderatevigor and high vigor zone, were determined by plant cell density （PCD） obtained from aerialphotography in Pinot Noir vineyard. In general, with the increase of vine vigor, theconcentrations of some esters and alcohols were decreased. The levels of terpenoids includinglinalool and nerol in wines from ultra low vigor were higher than those from other vine vigorzones with the exception of citronellol. Meanwhile, with the decrease of vine vigor, theconcentrations of vitispirane and β-ionone were increased. Based on the volatile composition,discriminant analysis illustrated the differences between wines from the four vine vigor zones.In addition, wines from ultra low vigor zones scored highest dark fruit, while those from highvigor zones scored the lowest. Wines from high vigor zones had the highest level ofherbaceous character, while ultra low vigor had the lowest. The results demonstrate thepotential of remote sensing as a rapid method to delineate vine vigor zones, producing wineswith high quality.6The effect of grape berry B. cinerea infection on volatile compounds of the resulting wines was investigated. Different levels of B. cinerea infected grapes （1%,2.5%,5%,10%,50%, w/w） harvested from Pinot Noir grapevines were fermented separately with healthygrapes as control. No significant difference was observed for the content of most of aromacompounds in wines from grapes with low B. cinerea infection rate （<10%）. Compared withhealthy wines, wines fermented from50%B. cinerea infected grapes had higher contents ofethyl heptanoate, ethyl2-phenylacetate, diethyl butanedioate, while lower levels of ethyl2-methylpropanoate, ethyl2-methyl butanoate, ethyl3-methylbutanoate. The concentrationsof heptan-1-ol and1-octen-3-ol in wines fermented from50%B. cinerea infected grapes weresignificantly higher than those from healthy grapes, while the content of3-methylbutan-1-olwas lower. In addition, the concentrations of linalool and citronellol in wines from grapeswith low B. cinerea infection rate （<10%） were slightly higher than those in healthy wines,although, with the increase of B. cinerea infection rate, the concentrations of terpenes such aslinalool, citronellol, nerol in the resulting wine were decreased, while the contents of nonanal,benzaldehyde and1-octen-3-ol were increased. The content of C₁₃-norisoprenoids was notaffected by B. cinerea infection.