Hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides. Optimum pH is 7.2. Optimum temperature is 30 degrees Celsius with o-nitrophenyl-beta-D-galactopyranoside (ONPG) as substrate. Has high specific activity at low temperatures. By growth on lactose. Belongs to the glycosyl hydrolase 2 family.