Hydrolysis of lactose using β-d-galactosidase immobilized in a modified Arabic gum-based hydrogel for the production of lactose-free/low-lactose milk

Abstract

β-d-galactosidase was immobilized in a modified Arabic gum-based hydrogel for the hydrolysis of standard lactose and lactose contained in UHT milk with the aim of producing lactose-free/low-lactose milk. The hydrogel was synthesized by cross-linking the modified Arabic gum with acrylamide, using potassium persulfate as initiator. Fourier-transform infrared spectroscopy and scanning electron microscopy confirmed the formation of the hydrogel and its three-dimensional porous network. Swelling degrees in distilled water, drinking water, phosphate buffer solution at pH7.0 and acetate buffer solution at pH4.0 were 12.56 and 17.72, 10.65 and 12.58, 8.58 and 10.71, and 6.49 and 8.16g water per g dried hydrogel at room temperature and 37.0±1.0°C, respectively. The immobilization capacities of β-d-galactosidase in acetate and phosphate buffer solutions at room temperature were 242.52±0.13 and 118.42±0.23mg enzyme per g dried hydrogel, respectively, after 1440min of contact. Higher enzymatic activities were found after immobilization in phosphate buffer solution due to the isoelectric point of β-d-galactosidase. Hydrolysis of standard lactose and lactose contained in UHT milk was more efficient using immobilized β-d-galactosidase than free β-d-galactosidase. Immobilized β-d-galactosidase was applied for three cycles of hydrolysis of lactose without significantly losing enzymatic activity.

Keywords: Enzyme; Hydrogel; Immobilization; Lactose; β-d-galactosidase.