Effects of Preflowering Leaf Removal on Phenolic Composition of Tempranillo in the Semiarid Terroir of Western Spain

The effects of preflowering defoliation on the qualitative and quantitative composition of phenolic compounds in the grape skins of Tempranillo grapevines grown in a semiarid terroir of western Spain, Badajoz, were determined. Control vines were compared with defoliation carried out before flowering (ED) in 2009 and 2010. Forty-two phenolic compounds were identified and quantified in the grape skins, including anthocyanins, flavonols, flavanols (cathechin and epi-cathechin and the flavanol dimmers B1, B2, and B3), and hydroxycinnamic acids, as both simple and conjugated molecules. ED did not significantly alter the concentration of total anthocyanidins, although in 2009, 3-O-acylated monoglucosides and p-coumaroylglucoside forms were more abundant in this treatment. A nonsignificant tendency toward increased total flavanols due to defoliation treatment was observed. Leaf removal increased concentrations of flavonols (glycosides of myricetin, quercetin, kaempherol, and isorhamnetin), hydroxycinnamic acids, and stilbenes in season-specific ways. Preflowering leaf removal may contribute to increased concentrations of compounds that can form complexes with anthocyanins (copigments) and may thus improve wine color stability.