CHARACTERIZATION OF PECTIN METHYLESTERASE AND POLYGALACTURONASE EXTRACTED FROM FRESH-CUT MELON.

Pectin methylesterase (PME) and polygalacturonase (PG), the main enzymes involved in softening process of minimallyprocessed fruit and vegetables, were extracted from two different varieties of melon fruit (Cucumis melo cantalupensis cv.‘Charentais’ and inodorus cv. ‘Amarillo’) and characterized using reliable spectrophotometric methods. In all cases the enzymesfollowed the Michaelis—Menten kinetics, showing differentvalues of PG kinetics parameters between the two cultivars: Km = 0.05±0.005 U/g (Charentais) and 0.24±0.02 U/g (Amarillo);Vmax = 188.9±31.4 U/g (Charentais) and 300.9±64.0 U/g (Amarillo). Optimal temperature of activity in both cultivars was 40◦C forPME and 60◦C for PG. PME was much more thermolable comparedwith PG above all in cv. Amarillo, loosing over 90% of relative activity after only 5 min of incubation at 70◦C. PME activation energy resulted then much higher than PG (DeltaE# = 59.3 kJ mol−1 and 183.2 kJ mol−1 for ‘Charentais’and ‘Amarillo, respectively). Inhibition tests by sugars evidenced a decreasing course of both activities as D-fructose concentration in the assay medium increased.