Anthocyanin accumulation and extractability during the maturation of the grapes of three varieties

Abstract

Anthocyanin accumulation and extractability were studied in Tannat, Cabernet Sauvignon and Merlot grapes produced in the south of Uruguay in two consecutive seasons. Typical cultivation situations employed in the region for each variety were considered. A follow-up was carried out, considering 60 plants per vineyard, and the harvest was determined according to the technological indices of maturity. Samples of grapes were taken in duplicate in each vineyard periodically along grape maturation. The basic composition, polyphenolic potential and anthocyanin extractability were determined. Also, half of grapes were frozen and later peeled; skin extractions over 24 hs with a solution of 12% ethanol and pH 3.2 were carried out. The anthocyanin contents of the extracts obtained were determined by HPLC-DAD. The levels of anthocyanins reached the highest values before technological maturity. Anthocyanin extractability had a decrease during grape maturation. The highest levels of anthocyanins were found in Tannat skins altough those of Cabernet Sauvignon were higher than those of Merlot grapes. Anthocyanin profiles of skins changing significantly after veraison but these changes were very lower just before maturity, found the typical values of each variety The prevalent anthocyanin derivatives at the start of the maturation showed a decrease during the process. Malvidin proportions increased and cyanidin proportions decreased along the first stages of maturation, in agree with the biosynthesis of anthocyanins. Malvidin derivatives showed the fastest accumulation. At harvest, Tannat berries presented the highest sugar contents, total acidity, total polyphenol richness, total potential in anthocyanins and potential in extractable anthocyanins, and the lowest pH values. Tannat had the highest values of EA%, corresponding to the lowest extractability of anthocyanins. Significant differences among the anthocyanin profiles and contents of the grapes of each variety were found. The tri-hydroxylated molecules were prevalent respect to the di-hydroxylated anthocyanins in the three varieties. Tannat skins had the highest proportion of non-acylated glucosides, petunidin and delphinidin derivatives. Cabernet Sauvignon skins had the highest proportions of acetylated glucosides and malvidin derivatives. Merlot skins presented the highest proportions of coumaroyl glucosides and peonidin derivatives. It can be concluded that the grape variety and the environmental conditions determined important differences in the anthocyanin composition of grapes and the extractability of these compounds from the skins. The anthocyanin contents and profiles of the grapes of each variety presented high differences that might determine important variations in the colour and composition of the respective wines.