The kinetics of inactivation of pectin methylesterase and polygalacturonase in tomato juice by thermosonication

The ultrasonic inactivation kinetics of polygalacturonase (PG) and pectin methylesterase (PME) in tomato juice were studied at a frequency of 20 kHz, amplitude of 65 μm and temperatures between 50 and 75 °C. Thermal treatments at the same temperatures were conducted to separate the effects of heat and ultrasound. The thermal inactivation of PG was described by a fractional conversion model with PG 1 remaining stable, whereas the inactivation of PG by combined ultrasonic and heat treatment (thermosonication) was best described by first order biphasic kinetics, with both PG1 and PG2 inactivated at different rates. The thermal and thermosonication inactivation of PME was described well by first order kinetics. The inactivating effect of combined ultrasound and heat was synergistic. Thermosonication enhanced the inactivation rates of both PME and PG. The inactivation rate of PME was increased by 1.5–6 times and the inactivation rate of PG2 by 2.3–4 times in the temperature range 60–75 °C, with the highest increase corresponding to the lowest temperature.