Changes in the Free and Total Amino Acid Composition of Several Vitis Labruscana Grape Varieties During Maturation

Abstract

The changes in concentration of the free and total amino acids and other chemical constituents of three commercially important Vitis labruscana grape varieties during maturation were examined. The most abundant of the free amino acids of the varieties Concord, Catawba, and Delaware were α-alanine and arginine. At maturity, concentrations ranged from 29.4 to 97.8 mg/100 ml of juice for α-alanine and 32.8 to 48.0 mg/100 ml of juice for arginine, respectively averaging 30.8 and 22.2% of the total free amino acid composition. The remaining free amino acid values ranged between 1 and 10 mg/100 ml of juice. The reason for the large amounts of α-alanine in V. labruscana compared with V. vinifera cultivars is unknown.

Small quantities of β-alanine and ornithine were found in all three varieties, and citrulline appeared in Concord and Catawba. Concord was the only variety found to contain traces of α-amino-n-butyric acid.

The amino acids present in greatest amounts following acid hydrolysis for determining total amino acid contents at maturity were glutamic acid (29.1%), α-alanine (20.7%), and arginine (13.6%). Analysis of the data revealed that α-alanine and arginine existed primarily in the free state in the grape musts, while glutamic and aspartic acids were extensively bound in protein and polypeptides.

During the ripening period the total acidity decreased in Concord, Catawba, and Delaware grapes to respective levels at maturity of 1.32, 1.82, and 1.03%. Soluble solids and color formation increased during maturation. The time of véraison for each variety was estimated from the data.

For the most part, the free and total amino acids began to increase during the véraison and postvéraison periods in all three cultivars. The commencement and rates of these increases, however, varied among individual amino acids and varieties.