Batch and continuous synthesis of lactulose from whey lactose by immobilized β-galactosidase

In this study, lactulose synthesis from whey lactose was investigated in batch and continuous systems using immobilized β-galactosidase. In the batch system, the optimal concentration of fructose for lactulose synthesis was 20%, and the effect of galactose, glucose and fructose on β-galactosidase activity was determined for hydrolysis of whey lactose and the transgalactosylation reaction for lactulose synthesis. Galactose and fructose were competitive inhibitors, and glucose acted as a noncompetitive inhibitor. The inhibitory effects of galactose and glucose were stronger in the transgalactosylation reaction than they were in the hydrolysis reaction. In addition, when immobilized β-galactosidase was reused for lactulose synthesis, its catalytic activity was retained to the extent of 52.9% after 10 reuses. Lactulose was synthesized continuously in a packed-bed reactor. We synthesized 19.1 g/l lactulose during the continuous flow reaction at a flow rate of 0.5 ml/min.