engleski

Prolonged ripening on the vine affects the polyphenolic profile of grapes and wine ‘Plavac Mali’ (Vitis vinifera L.)

Prolonged grape ripening beyond phenolic and technological ripeness is a common practice in Mediterranean vineyards. It is believed to increase overall wine quality, although the chemical composition of those wines is poorly understood. This vineyard practice is common in the Mediterranean part of Croatia where ‘Plavac mali’ is widely grown to produce premium red wines. The aim of this study was to quantify the compositional differences in polyphenolic profile, and physicochemical parameters of grapes, and corresponding wines of ‘Plavac mali’ at five different harvest dates. Ethanol concentration was in the range of 9.9 to 14.5 %. Prolonged ripening enhanced anthocyanin, and flavonol concentration in skin tissue, with the exception of 3-O-glucoside of delphinidin, petunidin, quercetin, and 3-O-rutinoside of quercetin. Various trends in skin low molecular weight phenolic compounds were detected: increase in (+)-gallocathechin and (-)-epicatechin, and decrease in the others ((+)-catechin, (-)-epigallocatechin, and proanthocyanidins (B1, B2, B3, B4)). Grape seeds reached stable concentration of the low molecular weight phenolic compounds in 3rd harvest date, while prolonged ripening had a significant influence on (-)-epicatechin, and (-)-epigallocatechin. In contrast, in corresponding wines anthocyanins concentration had two peaks in 3rd and 5th harvest date, without any significant difference between those two, except in peonidin- 3-O-glucoside. Prolonged ripening resulted in wines with high concentration of (+)-gallocatechin, (-)-epicatechin, and the lowest concentration of the (-)-epigallocatechin. Various trends were detected for flavonols and phenolic acid compounds with regard to cofactor color activity. Grape reached phenolic maturity in 3rd harvest date. Phenolic composition of ‘Plavac mali’ can be improved with the practice of prolonged ripening. Negative effects of prolonged grape ripening should also be taken into account such as: decrease in grape yield, primary amino nitrogen, total acidity, increase in sugars and pH. The results indicate good potential of ‘Plavac mali’ for prolonged grape ripening but negative aspects should also be considered.

flavonoids, anthocyanins, proanthocyanidins, (+)-catechin, postharvest overripeness, Mediteran climate

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