THERMAL INACTIVATION KINETICS OF PECTINESTERASE IN ACIDIFIED PAPAYA NECTAR AND PUREES

This study reports on thermal inactivation of papaya pectinesterase (P E), whose activity in papaya products causes problems of gelation and clumping. The PE kinetics of inactivation in papaya purees of pH 4.0, 3.8 and 3.5 and in a nectar of pH 3.8 and 14-degrees-Brix, were determ ined by the pH static method in the temperature range of 75 to 85-degr ees-C. The thermal inactivation of PE followed a first order kinetics with constants that varied from 1.05 x 10(-3) s-1 (D = 36.6 min) to 8. 00 x 10(-3) s-1 (D = 4.8 min) for pH 4.0 puree and 75-degrees-C, and p H 3.5 puree and 85-degrees-C, respectively. The inactivation constants for the nectar PE were 20 to 27% lower than the ones obtained with th e puree of the same pH. The inactivation energies and the z values for the PE inactivation varied around 40 Kcal/mol and 14-degrees-C, respe ctively. The free energies (DELTAG approximately 25 Kcal/mol) and ent halpies (DELTAH approximately 38 Kcal/mol) of the transition state ar e typical of protein denaturation process and indicate that in the ina ctivation, eight non-covalent bonds are broquen.