Changes in the aromatic composition of the Vitis vinifera grape Muscat Hamburg during ripening

A two-year study was carried out to determine the evolution of free and bound aromatic compounds of Muscat grape (sp. Vitis vinifera cv. Muscat Hamburg) during ripening. The most abundant free compounds detected were linalool, geraniol, citronellol, nerol, 3,7-dimethyl-1,5-octadien-3,7-diol (diendiol I) and 3,7-dimethyl-1,7-octadien-3,6-diol (diendiol II). In general, concentrations of the main free terpenols increased during grape development, except geraniol. In the glycosidically-bound fraction the major compounds were geraniol, linalool, citral, nerol, citronellol, α-terpineol, diendiol I, diendiol II, trans-furan linalool oxide (linaloloxide I), cis-furan linalool oxide (linaloloxide II), benzyl alcohol and 2-phenylethanol. At grape maturity, results showed a higher content of bound compounds than of free forms, with the exception of linalool, diendiol I, and diendiol II whose concentrations were greater in the free fraction, and limonene which was not detected in the bound fraction. On the basis Odour Activity Values, linalool was the most odour-active odorant. Other monoterpenes potentially contributing to Muscat aroma were rose oxide, citral, geraniol, nerol and citronellol.