ARS | Publication request: Influence of kaolin particle film and deficit irrigation on varietal aroma components in Merlot grape (Vitis vinifera L.)

Submitted to: Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 28, 2012
Publication Date: September 15, 2012
Citation: Song, J., Shellie, K., Wang, H., Qian, M.C. 2012. Influence of kaolin particle film and deficit irrigation on varietal aroma components in Merlot grape (Vitis vinifera L.). Food Chemistry. 134(2):841-850.

Interpretive Summary: Aroma is detected by receptors in the nasal pathway of humans when very small chemical compounds become airborne or volatile. Volatile aroma compounds in grapes develop during berry development and contribute to the sensory quality of the resulting wine. Imposing a water stress to the grapevine during berry development has been shown to alter fruit composition at harvest, but little is understood about its effect on grape aroma compounds. Grape composition at harvest has also been shown to be sensitive to sunlight exposure and ambient temperature during berry development. Berries grown on vines under a water stress have a higher risk of heat stress and radiation damage due to less available shading from the vine canopy. Foliar application of a kaolin-based particle film (PF) has been shown to reduce heat stress in many crops. In this study, we measured the influence of PF on the composition of grape aroma compounds in Merlot grapevines grown in the high desert region of southwestern Idaho under differing levels of water deficit. Vines with or without PF were irrigated to meet 100, 70, or 35% of estimated crop evapotranspiration (ETc) from fruit set through harvest, or 35% ETc from fruit set until veraison and then 70% ETc until harvest. Grapes sampled at maturity were used to measure the concentration of free and bound aroma precursors using a technique called stir bar sorptive extraction-gas chromatography-mass spectrometry. The only detected effect of PF was an average decrease in free 1-octen-3-ol; however, water deficit decreased free C6, lipid-derived compounds and increased free and bound ß-damascenone. The changes in grape aroma compounds observed in this study under water deficit were related to previously reported sensory perceptions of reduced herbaceous aromas and enhanced fruity notes.

Technical Abstract: The effect on grape-derived volatile composition of a kaolin-based, foliar reflectant particle film (PF) and differing severities of vine water deficit was investigated in this study over two growing seasons on Merlot grapevines grown in a semi-arid region of southwestern Idaho. Vines were provided with differential amounts of their estimated crop evapotranspiration (ETc) throughout berry development and PF was applied in a split-plot design to vines in half of each irrigation main plot, leaving unsprayed vines as controls. Free and bound flavor precursors in grapes were analyzed using stir bar sorptive extraction-gas chromatography-mass spectrometry (SBSE-GC-MS). Water deficit during berry development, on average over both years of the study, decreased free C6, lipid-derived compounds by 23 to 62%; increased the concentration of three carotenoid derived C13-norisoprenoids: free and bound ß-damascenone by 6 and 37%, respectively; bound 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) by 100% and bound 3-oxo-a-ionol by 54%. Water deficit also increased the concentrations of bound 1-octen-3-ol by 74% and the bound geraniol by 12%. The only detected main effect of particle film over both years of the study was an average decrease by 20% in free 1-octen-3-ol. The content of all volatile compounds and number of detected interaction effects were greater in the year that accumulated less heat prior to veraison. The changes in grape aroma compounds associated with vine water deficit are related to sensory perceptions of reduced herbaceous aromas and enhanced fruity notes.