Global grape aroma potential and its individual analysis by SBSE–GC–MS

Among the aroma compounds present within grapes, a significant part is assumed to come from specific odourless precursors found mainly as glycosidic compounds which are known as bound fraction. In this paper, the individual composition of non-aromatic red grape bound fraction has been assayed for first time by SBSE–GC–MS and compared with the global total aroma potential measured spectrophotometrically at the wineries, in which the anthocyanins interferences have been removed. Glycosidic aroma compounds have been extracted by macerating grapes with different extractants (EtOHaq or SO2) at different times and subjected to acidic hydrolysis at 70 °C for 2 h. The best extraction condition, expressed as the higher aroma compounds concentration (terpenes + C13 norisoprenoids + 2-phenylethanol + C6 compounds), was the ethanolic aqueous extraction carried out for 2 h, reducing considerably the extraction times proposed in the literature. The method was successfully used to discriminate non-aromatic red grape varieties, (Petit-Verdot, Merlot and Monastrell) being limonene, linalool, 2-hexen-1-ol, TDN and 2-phenylethanol the aromas that contributed most to the differentiation. An aromatic white table grape such as Early sugar was also assayed to check its higher volatile composition in comparison with the other red varieties. The percentage of favourable aromas (terpenes + C13 norisoprensoids + bencene derivates) is always higher than the unfavourable ones (C6) for all tested varieties, especially Early Sugar. It has also been observe that the spectrophotometric measurements are overestimated when compared with SBSE–GC–MS, probably due to the free sugar content and other glycosidic compounds.