Profiling Amino Acids in Wine Grapes with UHPLC-FLD

A recent study at the University of California, Davis set out to use a single method to profile 23 amino acids and glutathione in juices of four internationally relevant grape varieties grown under different soil and climatic conditions through a combination of double derivatizations reagents o-phthalaldehyde (OPA) and 9-fluorenylmethyloxycarbonyl (FMOC). The goal was to be able to validate a way to characterize the samples with a broad range of concentrations, which is very useful for efficiency and beneficial for making comparisons across those samples. The method was carried out by online pre-column derivatization followed by ultra-high performance liquid chromatography coupled with a fluorescence detector (UHPLC-FLD). A paper presenting the findings from this research was published by the Journal of Food Science (1).

Must (freshly crushed fruit juice that contains the skins, seeds, and stems of the fruit [2]) or juice nitrogen composition is important in the production of quality wine because it affects the growth and development of yeast during alcoholic fermentation (3). Amino acids are a source of nitrogen for yeast, as well as offering significant biological effects during the alcoholic fermentation process and are also precursors of aroma compounds in wines (4,5). Responsible for much of the total nitrogen content in grape must and wine (approximately 30%–40%), the primary amino acids are responsible for the largest fraction of grape juice's yeast assimilable nitrogen (YAN) content, a measure of primary amino acids and ammonia (6).

The study focused on Cabernet sauvignon, Cabernet franc, Merlot, and Petit Verdot grapes, four of the world's most known red wine grape varieties. Originally from France, these grape varieties spread across Europe and to California’s Napa Valley, Coonawarra region in Australia, and Maipo Valley in Chile, as well as Argentina, South Africa, and southern Brazil (7). Analysts report that the UHPLC-FLD method allowed quantifying 23 amino acids and glutathione in different grape varieties in 18 min of run-time. The most abundant amino acids, in concentrations above 603, 42.0, and 10.6 mg/L, were proline (PRO), gamma-aminobutyric acid (GABA), and arginine (ARG), which varied four-, four-, and 10-fold, respectively (1). This method showed a high sensitivity when compared to other methods in the literature that used OPA and FMOC (8) and dansyl chloride (9), and, once adapted for this work, achieved lower limit of detection (LOD) overall than similar methods in literature for wine and grape juice, while maintaining acceptable repeatability, reproducibility, and recovery with shorter analysis time (1).

The authors of the report state that the modified method enabled correlations among amino acids in juices (without the influence of winemaking) from the same grape varieties grown in different, internationally important wine regions to be assessed. With this method, it will be possible to extend these efforts to evaluate amino acid profiles in grape juices across different seasons and other grape varieties, which can additionally influence amino acid profiles (1).

Vineyards with grapevine and winery along wine road in the evening sun. © ah_fotobox - stock.adobe.com

References

1. Lima, M. M. M.; Choy, Y. Y.; Runnebaum, R. C. Comprehensive Amino Acids Profiling: Grape Varieties Grown in California and in Tuscany, Italy. J. Food Sci. 2024, Oct 16. DOI: 10.1111/1750-3841.17386

2. Must definition. Wikipedia. https://en.wikipedia.org/wiki/Must#:~:text=Must%20(from%20the%20Latin%20vinum,the%20first%20step%20in%20winemaking (accessed 2024-10-18)

3. Gutiérrez-Gamboa, G.; Carrasco-Quiroz, M.; Martínez-Gil, A. M.; Pérez-Álvarez, E. P.; Garde-Cerdán, T.; Moreno-Simunovic, Y. Grape and Wine Amino Acid Composition from Carignan Noir Grapevines Growing Under Rainfed Conditions in the Maule Valley, Chile: Effects of Location and Rootstock. Food Res. Int. 2018, 105, 344–352. DOI: 10.1016/j.foodres.2017.11.021

4. Callejón, R. M.; Troncoso, A. M.; Morales, M. L. Determination of Amino Acids in Grape-Derived Products: A Review. Talanta 2010, 81(4–5), 1143–1152. DOI: 10.1016/j.talanta.2010.02.040

5. Gutiérrez-Escobar, R.; Aliaño-González, M. J.; Cantos-Villar, E. Variety and Year: Two Key Factors on Amino Acids and Biogenic Amines Content in Grapes. Food Res. Int. 2024, 175, 113721. DOI: 10.1016/j.foodres.2023.113721

6. Waterhouse, A. L.; Sacks, G. L.; Jeffery, D. W. Amino Acids Metabolism. In Understanding Wine Chemistry, Sons, J. W. Ed. John Wiley & Sons, 2016, pp. 214-222. DOI: 10.1002/9781118730720

7. Chira, K.; Schmauch, G.; Saucier, C.; Fabre, S.; Teissedre, P. L. Grape Variety Effect on Proanthocyanidin Composition and Sensory Perception of Skin and Seed Tannin Extracts from Bordeaux Wine Grapes (Cabernet Sauvignon and Merlot) for Two Consecutive Vintages (2006 and 2007). J. Agric. Food Chem. 2009, 57(2), 545–553. DOI: 10.1021/jf802301g

8. Herbert, P., Santos, L., & Alves, A. Simultaneous Quantification of Primary, Secondary Amino Acids, and Biogenic Amines in Musts and Wines Using OPA/3-MPA/FMOC-Cl Fluorescent Derivatives. J. Food Sci. 2001, 66(9), 1319–1325. DOI: 10.1111/j.1365-2621.2001.tb15208.x

9. Tuberoso, C. I. G.; Congiu, F.; Serreli, G.; Mameli, S. Determination of Dansylated Amino Acids and Biogenic Amines in Cannonau and Vermentino Wines by HPLC-FLD. Food Chem. 2015, 175, 29–35. DOI: 10.1016/j.foodchem.2014.11.1