Effect of water availability on the phenolic content and tannin polymerization of Vitis vinifera L. cv. Syrah berry skins under semiarid climate

Abstract

Water regime is a major controllable factor in determining grape and wine quality in the vineyard. However, the effects of water conditions on grape phenolic composition are often contrasting depending on the severity of water restriction. In addition, the effect of water regime on tannin polymerization has not been extensively studied. In this work, the effect of irrigation on grape skin phenolic profile and polymerization was investigated in a vineyard of Northern Greece planted with Vitis vinifera cv. Syrah. Three irrigation treatments were applied, starting at berry set through harvest of 2011 and 2012: irrigation at 100% of crop evapotranspiration ETc (FI), irrigation at 50% of ETc (DI) and non-irrigated (NI). Berries were sampled at weekly intervals from veraison through harvest and skins were separated. Monomeric anthocyanins were determined in the skins by HPLC. Procyanidins were extracted with organic solvents and the average degree of polymerization (mDP) of the skin samples was determined by employing phloroglucinolysis followed by HPLC-UV and MS detection. NI grapes were characterized by increased anthocyanin and tannin concentration, with significant differences compared to DI and FI. Concerning proanthocyanidin structure, mDP of oligomeric fractions decreased (in 2011) while mDP of polymeric extracts increased during ripening (both years) in all treatments. NI grapes had higher mDP in skin polymeric tannin fraction in both years, while fewer differences among irrigation treatments were detected for the mDP of the oligomeric fraction. According to the results, management of vine water status could effectively control phenolic composition and structure of Syrah grapes. However, accumulation patterns of individual compounds in response to water conditions should be considered by winemakers to appropriately select harvest time according to winery objectives.