Immobilization of dextransucrase and its use with soluble dextranase for glucooligosaccharides synthesis

Four different preparations of immobilized dextransucrase from Leuconostoc mesenteroides L. were prepared: the native enzyme entrapped in alginate beads (Ia), the enzyme crosslinked with glutaraldehyde (GA) and then entrapped in alginate (Ib), and the native dextransucrase or the GA-crosslinked one entrapped in alginate beads, coated with chitosan film (IIa and IIb, respectively). These preparations and the soluble dextranase were used for isomaltooligosaccharides synthesis in 10% sucrose solutions, at pH 5.4 and 30 °C, in 10 consecutive 24 h reactions. The activity of the soluble dextranase in reaction mixtures was 4 U ml−1 and the activity of entrapped dextransucrase corresponded to 0.5 U ml−1. The high operational stability was observed for all these immobilized dextransucrase preparations which contained the crosslinked enzyme. The best results were achieved for dextransucrase crosslinked with 10% GA. In the first process, the conversion of sucrose was 90%, and it dropped to 60–70% from the sixth batch. The final mixtures of products contained 55–60% isomaltose (IM), 20% glucose (Glc), as well as isomaltotriose (IM3) and tetraose—10–15% of each, and only traces of leucrose.