The experiment was carried out in a semi-arid terroir of western Spain, Badajoz, to determine the effects of perflowering defoliation on the qualitative and quantitative composition of phenolic compounds in the grape-skins of Tempranillo grapevines. Control vines (C) were compared with defoliation carried out before flowering (ED) in seasons 2009 to 2010. A total of 42 phenolic compounds were identified and quantified in the grape skins including anthocyanins, flavonols, and hydroxycinnamic acids, both as simple and as conjugated molecules, and also flavanols (cathechin and epi-cathechin and the flavanol dimmers B1, B2 and B3). ED treatment did not significantly affect concentration of total anthocyanidins with respect to the control, non-defoliated vines, although in 2009 3-O-acylated monoglucosides and p-coumaroylglucoside forms were increased by prebloom leaf removal. A tendency for the amount of total flavanols to increase due to defoliation treatment was observed but was not significant. Also leaf removal increased concentration of flavonols (glycosides of myricetin, quercetin, kaempherol and isorhamnetin) as well as hydroxycinnamic acids and stilbenes in different ways depending on season. Preflowering leaf removal may contribute to increase concentration of compounds with the ability to form complexes with anthocyanins (copigments), and is able to improving wine color stability.

A study was made of how water status (rainfed vs. irrigated) and crop load (no cluster thinning vs. cluster thinning) can together affect the grapes of Vitis vinifera cv. Tempranillo vines growing in a semiarid zone of Extremadura (Spain). The grapes were monitored at different stages of ripening, measuring the peroxidase (POX) and superoxide dismutase (SOD) antioxidant activities and the phenolic content (flavonoids and phenylpropanoids), together with other parameters. The irrigation regime was adjusted to provide 100% of crop evapotranspiration (ETc). The findings confirmed previous results that both thinning and water deficit advance ripening, while irrigation and high crop load (no thinning) lengthen the growth cycle. The SOD activity remained practically constant throughout ripening in the thinned treatments and was always lower than in the unthinned treatments, an aspect which could have been the cause of the observed greater level of lipid peroxidation in the water deficit, thinned treatment. The nonspecific peroxidase activity was very low, especially in the thinned treatments. The effect of thinning was enhanced when combined with water deficit, inducing increases in phenylpropanoids and, above all, flavonoids at the harvest stage of ripening, while leaving the polyphenol oxidase activity (PPO) unaffected.