ACTUAL BROWNING AND PEROXIDASE LEVEL ARE NOT CORRELATED IN RED AND WHITE BERRIES FROM GRAPEVINE (VITIS-VINIFERA) CULTIVARS

The measurement of the peroxidase activity (EC 1.11.1.7) in ten grapev ine cultivars (Airen, Clairette, Riesling, Servant, Carignan, Cinsaut Noir, Gamay Rouge, Grenache, Monastrell and Mourvedre) with o-phenylen ediamine as substrate reveals that peroxidase activity is not correlat ed with actual browning in either red or white cultivars, even under c onditions in which the catecholase activity of grape polyphenoloxidase is minimal. This is probably due to the fact that for peroxidase to a ct on flavonol and thocyanin substrates the previous action of alpha-a nd beta-glycosidases is necessary to remove sugar moieties from the gl ycosides in order to liberate the phenolic aglycones that are the true substrates of the enzyme.