A novel thermostable β-galactosidase from Bacillus coagulans with excellent hydrolysis ability for lactose in whey

beta-Galactosidase is one of the most important enzymes used in dairy industry. Here, a novel thermostable beta-galactosidase was cloned and overexpressed from Bacillus coagulans NL01 in Escherichia coli. The phylogenetic trees were constructed using neighbor-joining methods. Phylogeny and amino acid analysis indicated that this enzyme belonged to family 42 of glycoside hydrolases. The optimal pH and temperature were, respectively, 6.0 and 55 to 60 degrees C. The purified enzyme had a 3.5-h half-life at 60 degrees C. Enzyme activity was enhanced by Mn2+. Compared with other beta-galactosidases from glycoside hydrolase family 42, B. coagulans beta-galactosidase exhibited excellent hydrolysis activity. The Michaelis constant (K-m) and maximum rate of enzymatic reaction (V-max) values for p-nitrophenyl-beta-D-galactopyranoside and o-nitrophenyl-beta-D-galactopyranoside were 1.06 mM, 19,383.60 U/mg, and 2.73 mM, 5,978.00 U/mg, respectively. More importantly, the enzyme showed lactose hydrolysis ability superior to that of the commercial enzyme. The specific enzyme activity for lactose was 27.18 U/mg. A total of 104.02 g/L lactose in whey was completely hydrolyzed in 3 h with addition of 2.38 mg of pure enzyme per gram of lactose. In view of the high price of commercial beta-galactosidase, B. coagulans beta-galactosidase could be a promising prototype for development of commercial enzymes aimed at lactose treatment in the dairy industry.