Pectin Methylesterase Inactivation Kinetics in the Microwave Pasteurization of Mango Pulp and Nectar

This study investigates the thermal inactivation kinetics of pectin methylesterase (PME) in mango pulp and nectar (Palmer variety), using conventional and microwave heating. The aim was to provide practical processing parameters and examine potential non-thermal effects associated with microwave treatment. To ensure a proper comparison between heating technologies, similar temperature histories were obtained in paired experiments (conventional hot water bath vs. microwave reactor), with homogeneous sample temperature and full temperature history recorded (heating, holding, cooling). Samples (10 mL) were processed with temperatures between 50 to 80 °C and holding times between 2 and 101 s. A two-component first-order kinetic model with five parameters was adjusted (simultaneously solving the numerical integration of the temperature histories). For a reference temperature of 65 °C the D-values obtained were 4.964·10^-2 s and 92.57 s (conventional) and 2.691·10^-3 s and 79.82 s (microwave), with 55% of the initial acidity due to the thermolabile fraction. Predicted inactivation curves show that this thermolabile fraction is rapidly inactivated at 65 °C, while 1-2 min are required to bring the residual activity from the thermostable fraction down to 5%. PME showed to be more resistant in the mango pulp, requiring nearly 2 min to reach 10% at 75 °C. The comparison between conventional and microwave heating indicated the presence of non-thermal microwave effects at 55 and 60 °C; however, thermal effects dominate at practical processing temperatures, with no significant difference.

Keywords:
enzyme; thermal processing; heat treatment; juice; fruit

Experiments designed for fair comparison between conventional and microwave.

PME thermal inactivation follows two-component first-order kinetic model.

Thermolabile and thermostable fractions with large thermal resistance difference.

Non-thermal effects only at low T and thermal dominate at processing temperatures.