Ultrasonic inactivation tests with tomato pectinmethylesterase (PME) were conducted at cavitation intensities in the range of 0.004-0.020 mg L min(-1) (hydrogen peroxide yield rate) and at 50, 61, and 72 degrees C. Thermal only tests at 50, 61, and 72 degrees C were also conducted to delineate possible additive or synergistic effects. In thermal inactivation tests, the reduction in PME residual activity at 50 degrees C was negligible while D-values at 61 and 72 degrees C were 299.0 and 25.3 min. D-values varied from 24.0 to 240.6 min in sonication tests but were reduced to 0.3 min in the thermosonication test at 72 degrees C and cavitation intensity of 0.008 mg L-1 min(-1). Compared to the PME thermal inactivation test at 61 degrees C, thermosonication at the same temperature increased the inactivation by 39 to 374-fold, while at 72 degrees C the increase was 36-84-fold, depending upon cavitation intensity. Generally, the inactivation increased with temperature and cavitation intensity. A strong synergistic effect was observed in the thermosonication tests. The increase in the inactivation was more pronounced at low temperatures. The inactivation of tomato PME in all tests exhibited first order kinetics. (c) 2004 Elsevier Ltd. All rights reserved.