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Impact of grapevine vigour on aroma precursors in Vitis vinifera cv. Merlot
University of Stellenbosch. Department of AgriSciences. Department of Viticulture and Oenology
De Villiers, A
An important aspect of grape and wine quality that is often disregarded due to its complexity is that of aroma. This is often used as a marketing tool for wines following sensory analysis, but as yet has received little attention in our South African research context in terms of its chemistry. Current research is addressing questions of terroir, irrigation and optimal ripeness from various angles, including amongst others phenolic composition, but alongside this the question of aroma should follow suit. Aroma is complex at two levels, firstly the fact that it is difficult to measure analytically and secondly that the specific chemical compounds which define aroma vary between cultivars and even clones. In the final product, aroma can be defined and quantified through GC-MS analysis of specific volatile odorants, but to define these from their source in the grape berry has proven complex and difficult.
The carotenoids are a class of secondary metabolites in grape berries which have been identified as precursors to certain key odourants (the C13-norisoprenoids) in a variety of both red and white cultivars. The carotenoids are present at their highest concentration just prior to veraison, and are broken down during the ripening period. It is well documented in literature that the breakdown products of certain carotenoids become bound to glucose, and later form precursors to free C13-norisoprenoid odorants in wines. To quantify this pool of compounds, specifically those carotenoids which are known to form aroma compounds, will ultimately provide viticulturists and enologists with a measure of the potential quality of that fruit.