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

In this study, a thermostable (3-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 (Km) and maximum velocity (Vmax) values for lactose and o-nitrophenyl- (3-D-galactopyranoside (oNPG) hydrolysis were, respectively, 29.87 f 1.05 mM, 1.88 f 0.02 mu mol D-glucose released per min per mg of protein, and 0.067 f 0.003 mM, 1.70 f 0.05 mu mol o-nitrophenol (oNP) released per min per mg of protein. This (3-galactosidase is significantly activated by Mg+2 (2-10 mM) and slightly inhibited by D-glucose. The enzyme can also hydrolyze 57 f 3% of lactose after 12 h of reaction at 45 degrees 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.