BEHAVIOR OF PECTINASES EXTRACTED FROM MINIMALLY PROCESSED FRESH-CUT MELONS

Fresh-cut fruit is a segment of food industry that is developing fast due to the fact that it is a convenient food and has a fresh-like quality. However, the fresh-cut product is easily corrupted by some pectinases (pectin methylesterase, PME and polygalacturonase, PG especially) because in these technological conditions the enzymatic reactions tend to accelerate with consequent consistency loss of cell walls. Thus, to understand the mechanisms of degradation is necessary to know the behaviour of pectinases according to the environmental changes. PME and PG were extracted from freshcut cubes (2x2x2 cm) of two melon cultivars (Cucumis melo cantalupensis cv Charentais and inodorus cv Amarillo) harvested at commercial ripening (37 days after anthesis for Charentais and 45 days for Amarillo)and characterized using reliable spectrophotometric methods. Both enzymes followed the Michaelis-Menten kinetics. The PME activity at physiological pH value of melons (7.0) was 100% in both cultivars, while the residual PG was 91% in Charentais and 100% in Amarillo. Optimal temperature of activity was 40°C for PME and 60°C for PG in both cultivars. PME was much more thermolabile compared with PG and above all in Amarillo, loosing over 90% of relative activity after only 5 minutes of incubation at 70°C. PME activation energy resulted then much higher than PG. Inhibition tests by sugars (D-glucose and D-fructose) evidenced a decreasing course of both activities as D-fructose concentration in the assay medium increased.