Monoterpene composition grapes

Williams, RJ., Strauss, C.R., Wilson, B., Massy-Westropp, R.A. (1982b). Studies on the hydrolysis of Vitis vinifera monoterpene precursor compounds and model -D-glucosides rationalizing the monoterpene composition of grape. J. Agric. Food Chem., 30, 1219-1223. 

Changes in monoterpene composition with grape development. Several studies have been conducted in which changes were recorded in the concentration of free monoterpenes in ripening grapes (11,38,64-66) However, most of these works were carried out before the presence of glycosidically bound or polyhydroxylated forms of monoterpenes in fruit were recognized. 

Effect of wine ageing on monoterpene composition. Several studies have been made in which alterations in monoterpene distribution in wines over time or with increases in temperature were recorded (84-89). The effect on wine flavor of prolonged ageing or exposure to elevated temperatures is a loss of fruit bouquet. By contrast, brief heating of juices of aromatic grapes can enhance the fruit flavor by increasing the concentration of free volatile monoterpenes through hydrolysis of precursors. 

Vltlcultural aspects. Vitlcultural research would benefit from detailed investigations concerning influences of major preharvest variables on monoterpene composition of fruit. Different pruning techniques, trellis designs, soil characteristics and climatic variables have yet to be assessed for their impact on grape flavorants. Research has been carried out on some of these factors in relation to wine quality (92,93) and now their effect on fruit... 

Numerous volatiles are released upon hydrolysis of glycoside isolates (1, 13), many of which are presumed to be acting as flavor compounds. Different grape varieties apparently produce glycosides which, when hydrolyzed, release differing proportions of monoterpenes, Cn norisoprenoids and benzene derivatives, as well as other volatiles. However, there is little reliable aroma threshold information regarding many of these compounds, and there has been no systematic attempt to relate the volatile composition of the hydrolysates to their sensory properties. 

Formation and metabolism of monoterpenes by yeasts. Although certain species of yeasts are capable of producing monoterpenes (80,81), the wine yeast species Saccharomyces cerevlslae appears not to share this capacity (82). Accordingly, it has been concluded that terpene composition in various grape cultivars and varietal wines is not Influenced by fermentation (6,82). Although apparently unable to biosynthesize monoterpenes, wine yeasts may carry out certain transformations of these compounds (e.g. double bond reduction) (83). 

---