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β-Galactosidase encoding genes lacLM from Lactobacillus helveticus DSM 20075 were cloned and successfully overexpressed in Escherichia coli and Lactobacillus plantarum using different expression systems. The highest recombinant β-galactosidase activity of ∼26 kU per L of medium was obtained when using an expression system based on the T7 RNA polymerase promoter in E. coli , which is more than 1000-fold or 28-fold higher than the production of native β-galactosidase from L. helveticus DSM 20075 when grown on glucose or lactose, respectively. The overexpression in L. plantarum using lactobacillal food-grade gene expression system resulted in ∼2.3 kU per L of medium, which is approximately 10-fold lower compared to the expression in E. coli . The recombinant β-galactosidase from L. helveticus overexpressed in E. coli was purified to apparent homogeneity and subsequently characterized. The K  m and v  max values for lactose and o -nitrophenyl-β-d-galactopyranoside ( o NPG) were 15.7 ± 1.3 mM, 11.1 ± 0.2 µmol D-glucose released per min per mg protein, and 1.4 ± 0.3 mM, 476 ± 66 µmol o -nitrophenol released per min per mg protein, respectively. The enzyme was inhibited by high concentrations of o NPG with K  i,s = 3.6 ± 0.8 mM. The optimum pH for hydrolysis of both substrates, lactose and o NPG, is pH 6.5 and optimum temperatures for these reactions are 60 and 55 °C, respectively. The formation of galacto-oligosaccharides (GOS) in discontinuous mode using both crude recombinant enzyme from L. plantarum and purified recombinant enzyme from E. coli revealed high transgalactosylation activity of β-galactosidases from L. helveticus ; hence, this enzyme is an interesting candidate for applications in lactose conversion and GOS formation processes.

β-Galactosidase from Lactobacillus helveticus DSM 20075: Biochemical Characterization and Recombinant Expression for Applications in Dairy Industry