RIPENING STAGE INFLUENCED THE EXPRESSION OF POLYPHENOL OXIDASE, PEROXIDASE, PECTIN METHYLESTERASE AND POLYGALACTURONASE MELON CULTIVARS

The changes in degradative enzymatic activities (polyphenol oxidase, peroxidase, pectin methylesterase and polygalacturonase) as well as in the main physical and chemical attributes during ripening of two melon types (C. melo var. cantalupensis'Galia' cv. and inodorus'Piel de sapo' cv.), harvested at three ripening stages were studied. A general decrease of enzymatic activities during ripening of both melon types was found. A high correlation between cell wall degrading activities and melon softening was established. In particular, an increase of PG/firmness ratio in both melon types (r(2) coefficients of 0.99 and 0.83 for 'Galia' and 'Piel de sapo', respectively) was found. Results obtained confirm the role of PG in ripening-associated cell wall disassembly, in contrast with previous attempts to demonstrate that ripening-associated pectin degradation in melon is PG independent. As far as we know, the PPO changes during melons ripening have not previously reported. It was remarkable that in 'Galia' cv. PPO activity showed a very high correlation with colour changes and the PME/firmness ratio highly correlated with the ripening stage. However in 'Piel de sapo' cv. any of these correlations was found.