Development of a novel β-galactosidase/chitosan/ZIF8 composite beads-based biocatalyst: synthesis, characterization and application in whey valorization

Lactose hydrolysis by β-galactosidase enhances whey's commercial potential and promotes waste reduction and sustainability in a circular economy. Hydrolyzed whey is used as a sugar substitute and fermentable substrate for biofuels and other bioproducts. In this study, β-galactosidase was covalently immobilized on beads of a novel chitosan/zeolitic imidazole composite (Ch/ZIF8). The immobilization process on Ch/ZIF8 activated with glutaraldehyde (GA) (Ch/ZIF8-GA) was optimized using response surface methodology combined with Derringer's desirability function to achieve biocatalysts with high immobilization yield (IY) and activity. An IY of 38.59 % and immobilized β-galactosidase activity of 5.39 U/g were obtained with 3.6 % GA, 2.7 h of immobilization time, and 0.37 mg enzyme/g support. The immobilized enzyme (βGal@Ch/ZIF8-GA) showed a higher K m (10.42 mM) and a broadening of its pH-activity profile towards the acidic region compared to the free enzyme. Notably, βGal@Ch/ZIF8-GA exhibited enhanced thermal stability and maintained 74 % of activity after 9 months at 4 °C. Finally, whey lactose hydrolysis by βGal@Ch/ZIF8-GA was optimized, achieving 83.17 % hydrolysis with 0.27 g/mL composite/whey ratio after 14.5 h. The βGal@Ch/ZIF8-GA retained about 60 % of its initial activity after 12 reuse cycles. These results demonstrate the potential of βGal@Ch/ZIF8-GA as an efficient and stable biocatalyst for the valorization of whey. • Chitosan/ZIF8 composites as a support to covalently immobilize β-galactosidase. • High storage and thermal stability of the immobilized biocatalyst. • High operational stability of the immobilized enzyme hydrolyzing lactose in whey.