A batch catalytic process of fructooligosaccharide production with the initial sucrose concentration of 700 g dm(-3) was carried out in the temperature Interval of 67 5-78 degrees C to investigate the thermal stability of free Aureobasidium pullulans fructosyltransferase Inactivation experiments were carried out also for a saccharide-free solution in the temperature interval of 53 1-71 degrees C so that a stabilizing effect of saccharides contained in the reaction mixture could be assessed A model of enzyme inactivation kinetics based on a two-step sequential mechanism was developed and verified for both media using the multitemperature evaluation of inactivation data The model was used to predict the operational lifetime and optimal operational temperature of the biocatalyst. It was found that the use of the concentrated sucrose solution increases the operational temperature by about 15 degrees C compared to a dilute aqueous solution The value of 47 5 degrees C was estimated as an optimal temperature at which the enzyme operational lifetime would be 1year (C) 2010 Elsevier Inc All rights reserved