Relationship between varietal amino acid profile of grapes and wine aromatic composition. Experiments with model solutions and chemometric study.

Synthetic solutions containing amino acids, sugar, water, and yeast nutrients have been fermented by Saccharomyces cerevisiae, and the volatile composition of the fermented media has been analyzed by GC. Eleven amino acid compositions imitating the characteristic amino acid profile of 11 different grape varieties were tested. Significant differences in the levels of some important volatile compounds (ethanol, ethyl acetate, acetic acid, higher alcohols and some of their acetates, methionol, isobutyric acid, ethyl butyrate, and hexanoic and octanoic acids) were found. The levels of some of the volatile compounds are well correlated with the aromatic composition of wines made with grapes of the same varieties. A multiple linear regression study produced good models for most of the odorants for which the level was related to the must amino acid composition. Partial least-squares regression models confirm that amino acid composition explains a high proportion of the variance in the volatile composition and show that the relationship between both sets of variables is highly multivariate. According to the different models, the levels of some byproducts of fatty acid synthesis are related to threonine and serine, the level of beta-phenyletanol is closely related to the level of phenylalanine, and methionol is strongly correlated to the must methionine contents. The addition of selected amino acids to different musts confirms the previous observations.