Isolation and characterization of a β-galactosidase from Lactobacillus helveticus for industrial processing

Abstract

In this study, a thermostable β-galactosidase from Lactobacillus helveticus OSU-PECh-4A has been isolated through diafiltration and size-exclusion chromatography. The enzyme consists of a heterodimer with a molecular mass of 110 kDa, with a small and large subunit of 36 and 74 kDa, respectively. The Michaelis constant (K_m) and maximum velocity (V_max) values for lactose and o-nitrophenyl-β-d-galactopyranoside (oNPG) hydrolysis were, respectively, 29.87 ± 1.05 mM, 1.88 ± 0.02 μmol d-glucose released per min per mg of protein, and 0.067 ± 0.003 mM, 1.70 ± 0.05 μmol o-nitrophenol (oNP) released per min per mg of protein. This β-galactosidase is significantly activated by Mg⁺² (2–10 mM) and slightly inhibited by d-glucose. The enzyme can also hydrolyze 57 ± 3% of lactose after 12 h of reaction at 45°C and under a high concentration of lactose. We propose that this enzyme provides an important advantage from a practical and consumer point of view due to its origins as a probiotic source and improved features for important industrial applications, such as lactose hydrolysis and the potential to produce galacto-oligosaccharides.