Changes in the concentration of amino acids during the ripening of Vitis vinifera Tempranillo variety from the Denomination d'Origine Somontano (Spain)

The concentration of 18 free alpha-amino acids and total a-amino acid nitro gen in musts and total nitrogen in seeds, skins, and must of the Tempranill o variety was determined from the beginning of the ripening process until h arvest. Eighteen free alpha-amino acids were also determined for Riesling, Cabernet Sauvignon, and Moristel at harvest over a period of three consecut ive years in the Denomination d'Origine Somontano (Spain). Arginine, prolin e, histidine and glutamine were the most prominent amino acids in all four varieties. The predominant amino acid in Riesling and Cabernet Sauvignon wa s proline and arginine was the major amino acid in the Tempranillo variety in all the three years. In the case of the Moristel variety, arginine was t he predominant amino acid one year and proline the other two. The four majo r amino acids accounted for 62% to 88% of the total free alpha-amino acids. The amino acid nitrogen fraction in the juices ranged from 40% to 87% of t he total Kjeldahl nitrogen. The wine with the best characteristics was obta ined in the year in which total nitrogen concentration was the lowest and t he total free a-amino acid nitrogen concentration the highest. As the ratio of the four amino acids (proline, arginine, glutamine and histidine) to th e sum total of amino acids differed significantly from one variety to anoth er in this Denomination d'Origine, it was used as an index to differentiate between varieties from the same area. The sum total of amino acids increas ed during the ripening process, with individual amino acids varying from on e year to another. During the ripening period titratable acidity, melic and tartaric acid decreased in Tempranillo grapes all three years while berry weight, pH, degrees Brix, and total nitrogen increased. There was a good co rrelation between arginine and the accumulation of soluble solids during th e ripening process.