(361a) Chromatography Membrane Reactor System for the Continuous Synthesis of Galactosyl-Oligosaccharides

Beta-Galactosidase (EC 3.2.1.23), commonly known as lactase, catalyses not only the hydrolysis of lactose to the monosaccharides glucose and galactose but also the transgalactosylation reaction to produce galactosyl-oligosaccharides (GOS). GOS are non-digestible oligosaccharides which are recognized as prebiotics. Prebiotics have been found to reach the human colon without being hydrolyzed or absorbed in the upper part of the gastrointestinal tract. GOS selectively stimulate the growth of bifidobacteria in the lower part of the human intestine. Increase in the growth of bifidobacteria is usually accompanied by suppression of potentially harmful bacteria such as Clostridia and Bacteroides species in the intestine. GOS consist of a number of oligosaccharides with varying ß-glycosidic linkages depending on the enzyme source. There have been several investigations on the synthesis of GOS by ß-galactosidases from various sources. Some techniques have been developed for immobilization of ß-galactosidase including non-covalent adsorption, covalent binding, entrapment and encapsulation. Synthetic microporous membrane adsorbers as chromatographic media are an attractive alternative to traditionally used packed bed chromatography, which has several limitations. The adsorption of enzymes on ionic exchange resins is still the most popular, simplest and oldest technique for reversible immobilization of enzymes. The chromatography membranes are an ion exchange support containing functional quaternary amines or sulphopropyl groups e.g. supported cross-linked polyethersulfone (PES) or regenerated cellulose. The pores in the membranes are large enough to allow the biomolecules access to all the binding sites by direct fluid convection. This results in a very high capacity for large biomolecules. Pressure filtration forces the liquid through the micropores of the membrane, bringing target substances into direct contact with the binding sites. This direct convective transport to the binding sites minimizes the diffusion limitation of mass transfer without sacrificing capacity. The main applications of membrane adsorbers are separation and analysis of proteins. In our study, the membrane adsorbers have been investigated as an alternative support for immobilization of an enzyme to produce GOS. Some of the advantages of immobilizing enzymes via physical adsorption on an activated support are: the activated support is chemically inert, good stability during storage, controlled residence time on the enzyme, simple recovery of the enzyme after usage, the possibility of a continuous process in enzyme reactors and the elimination of carryover of the enzyme to the final product. This present study focuses on developing a method for immobilization of ß-galactosidase in a chromatography membrane, investigating the properties of the immobilized enzyme and the possibility of using the immobilized enzyme system for the synthesis of GOS from lactose. The ß-galactosidase from Kluyveromyces lactis was chosen as a model enzyme for this study. Different strongly basic anion exchange membranes were used here to achieve optimum conditions for the enzyme.