Changes in varietal volatile composition during shelf-life of two types of aromatic red sweet Brachetto sparkling wines

This work constitutes the first contribution to elucidate the varietal volatile composition of two types of sparkling wines manufactured with Brachetto grapes and its relative evolution during the shelf-life. After bottling, the volatile composition differed significantly among the typologies of sparkling wines evaluated, namely lightly ones (final bottle pressure < 1.7 bar) and fully ones (final bottle pressure > 3.0 bar). Free 2-phenyl ethanol was the major aromatic compound (71-78%) in Brachetto sparkling wines, but its concentration was significantly higher in fully ones. Among terpenoids, glycosylated geraniol was the predominant compound in the two types of sparkling wines, followed by nerol. These two compounds accounted for around 49% and 67% of bound aromatic precursors in lightly and fully sparkling wines, respectively. Lightly sparkling wines showed a significant lower content of four free terpenoids (trans-pyran linalool oxide, nerol, citronellol and 2,6-dimethyl-3,7-octadien-2,6-diol) in relation to fully ones, and a significant higher content of three free volatile compounds (geraniol, cis-pyran linalool oxide and cis-furan linalool oxide). A central composite design (CCD) and response surface methodology (RSM) were applied to evaluate and to predict the effect of two independent variables, time and temperature, on the varietal volatile composition and the overall olfactory attributes of both lightly and fully sparkling wines during their ageing in bottle. Significant quantitative changes were observed and some of them were satisfactorily predicted by the RSM approach. Values of the determination coefficient higher than 0.800 were obtained in both lightly and fully sparkling wines for free geraniol and glycosylated linalool, as well as for olfactory preferences. Significant correlations were also found among the overall olfactory judgement and some single free terpenoids correctly predicted by the mathematical model, preferentially α-terpineol and geraniol, although only the concentration of free geraniol was higher than its odour threshold. The higher presence of varietal geraniol was positively valued by the tasters.