Hydrolyzes 6-bromo-2-naphthyl-beta-D-galactopyranoside and o-nitrophenyl-beta-D-galactopyranoside (ONPG). Possesses a high level of transgalactosylation activity. Hydrolyzes lactose in milk. Hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides. By divalent metal ions. Fe(2+), Zn(2+), Cu(2+), Pb(2+) and Sn(2+) inhibit 52, 76.6, 85.3, 100 and 100% of the enzyme activity, respectively. Other metal cations and EDTA do not inhibit this enzyme. Thiol reagents 2-mercaptoethanol and dithiothreitol have no effect on the activity. Sulfhydryl group-blocking reagents p-chloromercuribenzoic acid and iodoacetic acid inhibit 86.2 and 74% of the enzyme activity, respectively. Optimum pH is 7.0. Retains more than 80% of the activity at a pH range of 6.0-7.5. Optimum temperature for the activity is 70 degrees Celsius using ONPG as substrate. Stable up to 70 degrees Celsius (PubMed:3086288). Retains 80% of the activity at 75 degrees Celsius (PubMed:18420605). Kinetics of thermal inactivation and half-life times at 60, 65 and 70 degrees Celsius are 120, 50 and 9 hours, respectively. Has potential for enzyme application in low-lactose milk production during milk pasteurization. Belongs to the glycosyl hydrolase 42 family.