Characterization of a glucosyltransferase from Erwinia sp. D12 and the conversion of sucrose into isomaltulose by immobilized cells

Erwinia sp. D12 is able to produce an isomaltulose synthase (EC 5.4.99.11) that converts sucrose into isomaltulose. The enzyme was partially purified using a two-step chromatographic process on DEAE-Sephadex A-50 and DEAE-Sepharose CL-6B. The molecular mass of 63 kDa was estimated by Sephadex G-200 gel filtration, and the Km and Vmax values determined for the enzyme were 138 mM and 9.81 μmol/min/mg protein with sucrose as the substrate, respectively. Enzyme activity was optimal at pH 6.0 and 40 °C. The glucosyltransferase was completely inhibited by Hg2+ and Ag+. An experimental design and response surface methodology were used to evaluate the influences of temperature, pH and substrate concentration on isomaltulose production from cells immobilized in chitosan. With the aid of a two-level full factorial design (23-FFD), the statistical analysis of the results showed that, in the range studied, the factors had a significant (p < 0.05) effect on isomaltulose production. The conditions that improved isomaltulose production were: temperature around 35 °C, pH 6.0 and sucrose concentration lower than 40%.