Purification and characterization of β-galactosidase from Aspergillus niger PQ570689 for lactose hydrolysis and prebiotic synthesis.

Abstract

β-Galactosidase converts lactose to galactose and glucose, and it is significant for lactose-intolerant people. A Nigerian local strain of Aspergillus niger (accession number PQ570689) previously isolated from fermented goat milk in Minna, Niger State, Nigeria, was used to produce β-galactosidase. Diammonium sulfate precipitation and gel filtration were used to purify the crude enzyme. The impacts of temperature (10, 20, 30, 40, and 50 °C), pH (4, 5, 6, 7, and 8), metal ions (Fe, Mn, Cu, and Mg), chemical activators/inhibitors (SDS and Tween-80), sugars (fructose, glucose, and sucrose), and substrate concentrations (o-nitrofenyl-beta-D-galaktopyranoside (ONPG)) on the purified enzyme activity were determined. The kinetic parameters including Vmax (maximum velocity) and Km (Michaelis-Menten constant) of the partially purified enzyme were also estimated. Afterwards, lactose hydrolysis and prebiotic production potential of the purified beta-galactosidase was evaluated using high-performance liquid chromatography (HPLC). The purified enzyme was characterized by the highest enzyme activity (338 U/mL), specific activity (18.82 U/mL per mg), and fold purification (35.78), as well as the least protein content (18 mg/mL). The purified β-galactosidase was most active at pH 7 and 50 °C. The enzyme was, however, inhibited by all the metal ions, surfactants, and sugars tested. This biocatalyst was characterized by a substantial catalytic capability (Vmax = 666.67 U/mL per min) and moderate affinity (Km = 8.67 mmol) to its substrate. The purified enzyme showed a great potential for lactose hydrolysis (> 99%) as well as a good prospect for prebiotics synthesis (7%). Thus, the β-galactosidase can be developed for various industrial, environmental, and biotechnological applications.