Evaluation of lactulose synthesis using immobilized β-galactosidase in different reactor configurations

Lactulose is a disaccharide composed of galactose and fructose. In the human body, it functions as a prebiotic, promoting the growth of beneficial bacteria, such as bifidobacteria and lactobacilli, in the gastrointestinal tract. Lactulose is produced via a transgalactosylation reaction between lactose and fructose, catalyzed by β-galactosidase. Prominent β-galactosidases used in lactulose synthesis include those from Aspergillus oryzae and Kluyveromyces lactis. Various methodologies have been developed to enhance the efficiency of enzymatic lactulose production. The objective of this study was to produce lactulose using β-galactosidase from K. lactis and A. oryzae, in both free and immobilized forms, and to evaluate operational conditions in different reactor configurations. Sugar concentrations in the medium and the lactose-to-fructose ratio were assessed to optimize lactulose synthesis. Experiments were conducted sequentially in a benchtop conical reactor with orbital stirring, a stirred-tank reactor with magnetic stirring, and a fixed-bed reactor. Sugar concentrations were determined using high-performance liquid chromatography (HPLC). Of the enzymes tested, only silica-immobilized K. lactis β-galactosidase failed to produce a substantial lactulose yield. All three reactor configurations proved suitable for lactulose production. Under the evaluated conditions, lactulose concentrations ranged from 19 to 30 g·L⁻¹. Among the tested systems, the stirred-tank reactor with magnetic stirring showed the most promising performance for lactulose production. These results highlight the potential of the enzymatic process for lactulose synthesis and provide valuable insights for future studies on the production of this prebiotic.