Abstract
White grapes (Chardonnay, Grechetto and Orvieto) were vacuum-pressed (up to -0.99·105 Pa) using two different 250-hL membrane presses (with or without nitrogen as a blanketing gas). Nitrogen gas increased the total phenolic content of the musts by 21% (Folin index) and 16% (HPLC method). The fraction of oxidized phenolics was inversely correlated with the total phenolic (Folin) index (R = -0.803, P = 0.0002). The strongest protective effect of nitrogen on phenolics was observed in Chardonnay and Grechetto musts, whose mean fraction of browned phenolics decreased by 87% and 10%, respectively, with respect to normal conditions. Total browning of the musts was significantly positively correlated with catechin (R = 0.590, P = 0.016) and gallic acid (R = 0.505, P = 0.046) only in the case of normal atmosphere. GRP was a marker of must oxidation only in the case of normal atmosphere (R = 0.737, P = 0.001), but was uncorrelated with total browning when the vacuum press tank was filled with nitrogen. Quercetin glucoside showed opposite correlations with respect to GRP. Nitrogen gas is therefore particularly recommended not only in positive pressure, but also for vacuum-pressing of white grapes containing high levels of catechin or gallic acid due to early harvest or peculiar varietal composition. © 2010 Elsevier Ltd.