Hydrolyzes p-nitrophenyl-beta-D-galactopyranoside (PNPG), o-nitrophenyl-beta-D-galactopyranoside (ONPG) and chromogen 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal), with highest activity against PNPG. Also acts on p-nitrophenyl-beta-D-glucopyranoside (PNPGlu) and o-nitrophenyl-beta-D-glucopyranoside (ONPGlu), but with significantly lower activity. Hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides. Strongly inhibited by glucose. No activity is lost during treatment with 100 mM EDTA after 2 hours. Activity not considerably affected by metal ions (5 mM), including Na(+), K(+), Mg(2+), Co(2+) and Ca(2+). Completely inhibited by Cu(2+) and Zn(2+) (5 mM) and is strongly inhibited by Mn(2+) (11%), Fe(2+) (25%) and Ni(2+) (38%) in comparison with the activity in the absence of cations (100%). Activity not affected by dithiothreitol, beta-mercaptoethanol and L-cysteine whereas reduced glutathione almost completely inactivates it. With ONPG as substrate, the addition of ethanol up to 20% still slightly stimulates activity. The activity increases up to 120% in the presence of 8% v/v ethanol at pH 5.5. Optimum pH is 6.5 with ONPG as substrate. Over 90% of activity in the pH range 6.5-8.5. Highly efficient at pH range 4.5-9.5. Optimum temperature is 50 degrees Celsius with ONPG as substrate. Active at 4-8 degrees Celsius. 60% of the maximum activity is detected at 25 degrees Celsius and 15% at 0 degrees Celsius. Over 50% activity at 30 degrees Celsius. Homotrimer. Has potential use in lactose removal in milk and dairy products at low temperatures and for cheese whey bioremediation processes with simultaneous bio-ethanol production. Belongs to the glycosyl hydrolase 42 family.