Experimental behavior of a whole cell immobilized dextransucrase biocatalyst in batch and packed bed reactors

Dextransucrases from Leuconostoc mesenteroides have been used to produce a diversity of controlled structure oligosaccharides with potential industria l applications. This is the case of alpha(1-->2) branched glucooligosacchar ides produced by L. mesenteroides NRRL B-1299 dextransucrase. In order to e stablish an industrial scale process with the immobilized enzyme, a biocata lyst was produced by whole cell entrapment in alginate beads. The main phys ical and physicochemical properties of the biocatalyst were determined and the hydrodynamic behavior in a packed bed reactor studied. It was possible to produce spherical beads of 0.2 cm diameter containing the insoluble part of L. mesenteroides culture (cells and insoluble polymer) with an activity of 4 IU/g. Immobilization yield reached 93% with an effectiveness factor o f 0.995 for particles of d(P) < 0.2 cm. Due to the complexity of dextransuc rase mechanism and kinetics, data obtained from initial rate measurements f ailed to describe the results obtained from the batch and continuous reacto rs. Therefore, apparent K-M and V-max data were used for the reactor modeli ng. It was found that under the conditions studied, the reaction rate was c ontrolled by external mass transfer limitations.