Changes in Concentration of Free and Total Amino Acids of Several Native American Grape Cultivars During Fermentation

Abstract

Changes in the concentrations of free and total amino acids of several commercial <i>Vitis labruscana</i> musts during fermentation were examined by automated ion-exchange analysis. Except for proline, lysine, and glycine, there was a dramatic reduction in free amino acid content by the sixth day after yeast inoculation. At the end of the fermentation the concentration of the free amino acids had increased through yeast cellular autolysis but were still only between 2 and 30% of the initial must values. Proline was apparently not utilized by the yeast during fermentation. Except for proline, which averaged 16.4 mg/100 ml wine, all the free amino acids were less than 3 mg/100 ml in the final wine samples. Small amounts of β-alanine, ornithine, and citrulline were found, and cystathionine was detected at the end of the fermentations. Total amino acid concentrations determined from hydrolyzed wine samples showed trends similar to those of the free amino acids during fermentation. Next to proline, the most abundant of the total amino acids were glutamic acid, aspartic acid, lysine, and glycine. In contrast to proline, which existed mostly in the free form, those four amino acids were present primarily in protein and polypeptide form. Levels of protein and total nitrogen decreased initially and then increased during the later stages of the fermentation. An average of 26.1% of the total nitrogen in the wine at the end of fermentation was due to free amino acid nitrogen. Ammonia, apparently readily utilized by the yeast, decreased rapidly during fermentation. The patterns of change in amino acid composition observed during fermentation were similar to those found with vinifera varieties. The differences were primarily quantitative.