New insights for the synthesis of galacto-oligosacharides with β-Galactosidase immobilized in silica

Galacto-oligosaccharides (GOS) are non-digestible and have a prebiotic effect. They stimulate the activity of beneficial bacteria and contribute to intestinal health. They can be synthesized enzymatically, with β-galactosidase being the enzyme that performs transgalactosylation. Enzymes in their free form can interfere with the process, so immobilization methods are used. Covalent bonding is one of these methods and silica has gained prominence as a carrier. Therefore, the synthesis of GOS was evaluated using commercial β-galactosidase produced in its free form and immobilized on silica. Buffer ionic strength and lactose concentrations were assessed. A Factorial Design was proposed to evaluate the influence of initial lactose concentration, agitation, and temperature on the synthesis of GOS. Magnetic and mechanical stirring and fixed-bed reactor configuration were also evaluated in the synthesis of GOS. GOS were produced in high concentrations of lactose (400 g L^-1), in the shortest time (3 h) for free enzyme and longest for immobilized enzyme (6 h). The effects of the Fractional Factorial Design variables were positive, the most effective influence was stirring, and the highest concentration of GOS was 67.70 g L^-1. GOS was synthesized with the immobilized enzyme at a concentration of 70.81 g L^-1 when using magnetic stirring and 90.37 g L^-1 with mechanical stirring. GOS concentrations remained at values higher than 30 g L^-1 in experiments in a fixed bed showing that β-Galactosidase immobilized on silica is promising for synthesizing GOS.