Comprehensive amino acids profiling: Grape varieties grown in California and in Tuscany, Italy

Twenty-three amino acids and glutathione were profiled in 33 juices: Cabernet sauvignon, Cabernet franc, and Merlot grown in Bolgheri, Tuscany, Italy, and Napa Valley, CA, as well as Petit Verdot grown in Napa Valley, CA. The method was carried out by online pre-column derivatization followed by ultra-high performance liquid chromatography with fluorescence detection; residual standard deviation values for repeatability (n = 20) were <5%. All amino acids could be successfully separated in these samples within 18 min. The most abundant amino acids, PRO, γ-aminobutyric acid, and ARG, varied by two-, two-, and three-fold, respectively, across all of the grape juices sampled. Comparisons between grape juices based on their geographic origin and variety were made with principal component analysis and hierarchical cluster analysis. Merlot juices from both regions were correlated differently by amino acids profile than Cabernet sauvignon and Cabernet franc juices. The amino acids profile in Merlot juices was more similar between most sites in Bolgheri. In contrast, Cabernet sauvignon and Cabernet franc juices had a higher similarity between vineyards in Bolgheri and vineyards in Napa Valley. Overall, most of the amino acids quantified in Cabernet franc juices and, to a lesser degree, Cabernet sauvignon juices from Bolgheri and Napa Valley vineyards were strongly correlated with each other.