Thermal inactivation of pectin methylesterase in pineapple juice

Thermal processing is usually used by the fruit juice industry for enzyme and microbial inactivation, thus limiting organoleptic changes that affect shelf life and quality of products. Mainly the inactivation of enzymes is necessary to avoid quality changes related to cloud loss, using mild temperature that allows minor alterations in product's sensory as well as in nutritive traits. Pineapple juice, a product obtained by diluting the concentrate juice and pasteurizing afterword shipped to Europe, has a high residual pectin methylesterase (PME) activity. In this view, the present work provides a detailed kinetic study of the effect of pasteurization on inactivation of PME in pineapple juice. The fresh juice was treated with temperatures ranging from 70 to 95 degrees C, for various times, until the complete denaturation of PME occurred. Results of thermal stabilization treatments showed that enzyme inactivation behaviour follows a first-order kinetic process, in the studied temperature range. Moreover, the reaction rate constants for denaturation of PME were determined; in particular, activation energy (Ea), decimal reduction time (D-ref), and z value (z), were 78.2 +/- 4.5kJ/mol, 16s (at reference temperature of 106 degrees C) and 36 +/- 3 degrees C, respectively. Based on the thermal resistance data here reported to inactivate PME, a treatment of 106 degrees C with a mean holding time of 1min should be employed in order to preserve cloudiness of pasteurized pineapple juice.