Studying pectin esterase inactivation behavior is important because it is responsible for the juice cloud stability loss, is composed of several isoenzymes and occurs naturally in orange. Freshly squeezed juice of 'pera' orange (Citrus Sinensis (L) Osbeck) was pasteurized at temperatures of 82.5 degrees C, 85.0 degrees C and 87.5 degrees C using ARMFIELD laboratory plate heat exchanger. At least five runs with different holding times were conducted for each temperature. As the obtained isothermal curves showed deviation from the expected first-order kinetics, data was statistically treated applying a non-linear regression and the estimated best fit was a three-parametermulticomponent-first-order model. At 82.5 degrees C, the isothermal curves showed a non-zero asymptote of inactivation indicating that at this temperature the most heat resistant isoenzyme could not be totally inactivated. The 87.5 degrees C isotherm showed the highest inactivation among the temperatures studied. These facts agree with the batch inactivation data found in literature, but the holding time required for a satisfactory inactivation was significantly smaller than the found in literature, suggesting that the proposed model can be used to design continuous process with more accuracy. (c) 2004 Elsevier Ltd. All rights reserved.