Volatile compounds and phenolic composition of skins and seeds of 'Cabernet Sauvignon' grapes under different deficit irrigation regimes

Aroma compounds and skin and seed polyphenols are determinants of wine composition. The aim of this study was to determine the effect of different post-veraison deficit irrigation strategies on volatile profile and the chemical composition of grape skin and seeds in a 'Cabernet Sauvignon' vineyard in Valencia (Spain). Besides a non-irrigated regime (rainfed), irrigation treatments consisted of replacing 25, 50 and 75 % of the estimated crop evapotranspiration (ETC). When compared to rainfed vines, watering during post-veraison at 75 % of the ETC, decreased concentrations of alcohols but increased those of aldehydes such as hexanal, related to herbaceous (non-desirable) aromas in wines. Irrigating at 25 % or 50 % of ETC resulted in similar concentrations of grape volatile compounds than rainfed vines. There was also a general trend in a reduction in skin to flesh ratio as irrigation regime increased. The concentration of skin anthocyanins and tannins increased with water applications, but seed tannins decreased in the most irrigated regimes. This suggests different effects of water stress on skin and seed polyphenol synthesis and accumulation. For the tannin content, water stress provoked higher tannin mean degree polymerization values, which positively affect must astringency. Under the experimental conditions of the present study, watering at 50 % ETC during post-veraison is the recommended irrigation strategy for optimizing grape composition and improving yield in comparison with rainfed vines.