Isomaltulose is a reducing disaccharide commercially produced from the enzymatic conversion of sucrose, catalyzed by a microbial glucosyltransferase. It is naturally found in small quantities in sugar cane extracts and honey. Not only does it have a low cariogenic potential, but it is also used in the food industry as a sucrose substitute. In this study, the concentrations of the additives polyethylenintine and glutaraldehyde in the process of alginate cell immobilization were optimized with the aid of an experimental design and response surface methodology. The highest conversion rate of sucrose into isomaltulose occurred after 12 h conversion in Erlenmeyer flasks at 30 degrees C with 150 rpm agitation. The statistical analysis at a confidence level of 90% produced a correlation coefficient of 0.90, and the polynomial model indicated 0.06% of glutaraldehyde as being the best concentration of this additive for the immobilization procedure. Under these conditions the immobilized cells showed better stability, and maintained a conversion rate above 50% after 282 h, as compared to cells without the additive. (c) 2006 Elsevier Ltd. All rights reserved.