Proline and arginine accumulation in developing berries of Vitis vinifera L. in Australian vineyards: Influence of vine cultivar, berry maturity and tissue type

Using HPLC analysis, free amino acid profiles were obtained for ripe berries of six grapevine cultivars (Cabernet Sauvignon, Grenache, Muscat Gordo, Pinot Noir, Riesling and Sangiovese) grown under comparable conditions and harvested at similar maturities. Compositional differences were observed between cultivars, however proline and arginine were always the major amino acids. Mature berries of Cabernet Sauvignon contained a very high concentration of proline, but a much lower concentration of arginine. Those of other cultivars contained moderate levels of both arginine and proline. Changes in free amino acid profiles during grape berry development were further investigated in four cultivars (Cabernet Sauvignon, Chardonnay, Gewurztraminer and Muscat Gordo). In all cases, most of the proline accumulation occurred late in ripening, around four weeks post-veraison. In contrast, arginine accumulation began before veraison and continued to full maturity, except for those cultivars in which a high concentration of proline accumulated, in which case the concentration of arginine reached a plateau relatively early in development. Accumulation of both proline and arginine appears to be developmentally regulated. These observations are discussed with reference to proline and arginine metabolism and possible links between them. The distribution of free proline, arginine and other amino acids amongst pulp, skin and seed was examined using mature fruit of Cabernet Sauvignon and Riesling. Amino acid profiles were found to vary considerably between the berry components. The skin contained a greater ratio of arginine:proline compared with the pulp. This suggests that the yeast-assimilable nitrogen content of juices, and therefore their fermentability, could be enhanced in the presence of skins

Assimilable nitrogen utilisation and production of volatile and non-volatile compounds in chemically defined medium by Saccharomyces cerevisiae wine yeasts

Surveys conducted worldwide have shown that a significant proportion of grape musts are suboptimal for yeast nutrients, especially assimilable nitrogen. Nitrogen deficiencies are linked to slow and stuck fermentations and sulphidic off-flavour formation. Nitrogen supplementation of grape musts has become common practice; however, almost no information is available on the effects of nitrogen supplementation on wine flavour. In this study, the effect of ammonium supplementation of a synthetic medium over a wide range of nitrogen values on the production of volatile and non-volatile compounds by two high-nitrogen-demand wine fermentation strains of Saccharomyces cerevisiae was determined. To facilitate this investigation, a simplified chemically defined medium that resembles the nutrient composition of grape juice was used. Analysis of variance revealed that ammonium supplementation had significant effects on the concentration of residual sugar, L-malic acid, acetic acid and glycerol but not the ethanol concentration. While choice of yeast strain significantly affected half of the aroma compounds measured, nitrogen concentrations affected 23 compounds, including medium-chain alcohols and fatty acids and their esters. Principal component analysis showed that branched-chain fatty acids and their esters were associated with low nitrogen concentrations, whereas medium-chain fatty esters and acetic acid were associated with high nitrogen concentrations.M. Vilanova, M. Ugliano, C. Varela, T. Siebert, I. S. Pretorius and P. A. Henschk