Volatile Constituents of Grape Leaves. I. Vitis Vinifera Variety 'Chenin Blanc'

¹ E. &. J. Gallo Winery, Modesto, California 95353.

'Chenin blanc' grape leaf volatile compounds were isolated by steam distillation. The distillate collected was extracted with pentane, and the compounds present were identified by gas chromatography/mass spectrometry. Prominent in grape leaves are the six-carbon compounds: cis-2-hexenal, trans-2-hexen-1-ol cis-3-hexen-1-ol, n-hexanol, trans-2-hexenol-1-ol, and cis-or trans-hexa-2,4-dienal. Also prominent are the terpenes and their derivatives: myrcene, linalool, alpha-terpineol, isopulegone, citral, geraniol, and ionone. Also identified were the sulfurcontaining compounds tetrathiocane and cis- or trans-3,5-dimethyl-1,2,4,-trithiolane. Sensory evaluation of the compounds exiting from gas chromatographic columns indicated that the six-carbon compounds were largely responsible for the "grassy" flavor from the leaves.

To confirm the influence of grape-leaf six-carbon compounds on wine grassy flavor, trans-2-hexenal, trans-2-hexenol, cis-3-hexenal, and n-hexenol in wine were evaluated by a taste panel. At 10 ppm or less, the compounds were detected at the 1% level of significance. To indicate whether six-carbon and other compounds might be released by macerated leaves in winemaking, wines were produced from grape juices containing 2% w/v leaves of which 0, 5, 15, and 25% w/w had been macerated. Taste-panel sensory evaluation of the wines indicated that 5% or more leaf maceration yielded wines of significantly lower quality.