Highly specific towards beta-D-galactoside substrates. Hydrolyzes 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) and o-nitrophenyl-beta-D-galactopyranoside (ONPG). Has activity against p-nitrophenyl(pNP)-beta-D-galactoside, but not significantly at all towards pNP-alpha-D-galactoside, pNP-beta-D-glucoside, pNP-beta-D-mannoside, pNP-beta-L-fucoside, pNP-beta-D-xyloside, pNP-beta-L-arabinoside, pNP-beta-D-galuronide, pNP-beta-D-glucuronide, pNP-beta-D-lactoside or pNP-beta-D-cellobioside. Hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides. Activity stimulated by beta-mercaptoethanol. Optimum pH is 6.6. Maintains activity over a broad range of pH values from 6 to 9. Optimum temperature is 45-50 degrees Celsius. Activity declines rapidly above 50 degrees Celsius. Stable for at least 70 hours at temperatures 35 degrees Celsius and below. At 50 degrees Celsius loses all activity in less than 15 minutes. Belongs to the glycosyl hydrolase 42 family.