Hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides. Binds 2 magnesium ions per monomer. Binds 1 sodium ion per monomer. Inhibited by zinc, copper and nickel ions. Activated by 2-mercaptoethanol and inhibited by EDTA in vitro. Optimum pH is 8.5. Optimum temperature is 4 degrees Celsius. It does not grow at temperatures higher than 25 degrees Celsius. Homotetramer. This cold-adapted beta-galactosidase could be used to hydrolyze lactose in milk and dairy products processed in refrigerated plants. It is in fact superior to the current commercial enzyme from K.marxiamus with respect to lactose removal, especially at low temperatures. Belongs to the glycosyl hydrolase 2 family.