Dynamic changes in absolute residual PME activity in potato tubers undergoing blanching were analysed with regard to the temperature distribution in the tissue after the treatment. The finite-element technique was used to predict the temperature distribution within the tissue during blanching. The temperature-related behaviour of the enzyme indicated that blanching between 60 and 70 degreesC induced thermal activation of PME in blanched potatoes. The temperature distribution in the tissue during blanching showed that activation takes place as soon as the tissue reaches an average temperature above 50 degreesC. However, the temperature dependence of the absolute residual PME activity in the tissue, when blanching at temperatures between 50 and 70 degreesC, did not follow Arrehenius' law. The degree of PME activity in the blanched tissue was found to depend on the "effective exposure time" to the temperature at which the activation/deactivation of the enzyme takes places. Thermal activation of PME in potato tissue occurred during the first two minutes of blanching. Longer heating times induced rapid deactivation of the enzyme in the tissue. (C) 2004 Elsevier Ltd. All rights reserved.