(481d) Immobilization of Bacterial Beta-Galactosidases Onto Nanofiltration Membrane and Its Application on Production and Separation of Galacto-Oligosaccharides

Galacto-oligosaccharides (GOS) are prebiotic functional foods that have many health benefits on human health by stimulating the growth and activity of Bifidobacteria in the colon. They are widely applied as non-digestible food ingredients in the nutritional market because of their beneficial health effects such as reducing serum cholesterol, reducing blood pressure, reducing toxic metabolites and undesirable enzymes, preventing constipation, and pathogenic and autogenic diarrhea. GOS can be produced from lactose by enzymatic transgalactosidation by β-galactosidase in either free or immobilized form. However, the same lactase enzyme also catalyzes the hydrolysis of lactose to glucose and galactose, which not only reduces GOS yield but also inhibits the enzyme reaction. It is thus desirable to remove glucose and galactose from the reaction medium to promote GOS production. As a result, the effect of product inhibiting reactions may be minimized in the trans-membrane system, which makes membrane an excellent enzyme support. The goal of this project is to evaluate the feasibility of enzyme immobilization on commercial nanofiltration (NF) membrane and its application on production and purification of GOS from lactose. In this work, Bacillus circulans lactase enzymes were immobilized on two types of commercial NF membrane sheets: polysulphone and Thin- Film composite membranes by using polyethyleimine (PEI). The principle of our immobilization method will base on the charge interactions on protein molecules and surface charges of the support membrane. PEI, a cationic hydrophilic polymer containing protonated or/and quarternized ammonium groups is used to attach the support membrane to convert its surface to positive charges. As a result, the protein molecule can be absorbed on the PEI-adsorbed membrane. The kinetics of membrane-immobilized enzyme reactions, both transgalactosidation and hydrolysis of lactose, were studied and compared with those from conventional enzyme reactions without simultaneous product separation. In the integrated biocatalytic membrane reaction, NF membrane retains the larger GOS molecules, while allowing the smaller monosaccharides to pass through. As a result, oligosaccharides are produced and purified at the same time. Additionally, There is no lactose lost in the permeate which will increase the recovery and product yield.