Optimization of lactulose synthesis from whey lactose by immobilized β-galactosidase and glucose isomerase

In the present study, commercially available whey was used as a lactose source, and immobilized β-galactosidase and glucose isomerase were used to synthesize lactulose from whey lactose in the absence of fructose. Optimal reaction conditions, such as lactose concentration, temperature, ionic strength of the buffer, and ratio of immobilized enzymes, were determined to improve lactulose synthesis using immobilized enzymes. Lactulose synthesis using immobilized enzymes improved markedly after optimizing the reaction conditions. When the lactulose synthesis was carried out at 53.5 °C using 20% (w/v) whey lactose, 12 U/ml of immobilized β-galactosidase and 60 U/ml of immobilized glucose isomerase in 100 mM sodium phosphate buffer at pH 7.5, the lactulose concentration and specific productivity were 7.68 g/l and 0.32 mg/U h, respectively. Additionally, when the immobilized enzymes were reused for lactulose synthesis, their catalytic activity was 57.1% after 7 repeated uses.