Predicting the end point of a blanching process

Thermal inactivation of peroxidase and lipoxygenase during blanching of a solid food with a finite cylinder shape (diameter = 9 cm and heitght = 20 cm) has been mathematically studied in order to evaluate the end point of the process. Predictions included thermal inactivation of peroxidase and lipoxygenase during heating in steam of a conventional blanching process, and thermal inactivation of lipoxygenase during an individual and quick blanching process. It was assumed an inactivation biphasic model to describe the inactivation first-order thermal kinetics of peroxidase and lipoxygenase. Heat transfer conditions, the total initial indicator enzyme activity, the proportion of resistant and labile isoenzymes, kinetic parameters and the end point that the analytical method to be used may detect are important factors to predict and optimize a blanching process. For the conditions evaluated the worst scenario was a total initial peroxidase or lipoxygenase activity of 500 UA/g, 10 % of resistant isoenzyme, being 1060 and 180 s, respectively, the heating times necessary to reach an end point of 1 UA/g. Heating times can be significantly reduced if an individual quick blanching process is used. (C) 2003 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.