Involved in galactan degradation (PubMed:27501980). Hydrolyzes galactooligosaccharides released by the endo-beta-1,4-galactanase GanB from galactan (PubMed:17056685, PubMed:27501980). Degrades galactotetraose, galactotriose and galactobiose, generating galactose as the end product (PubMed:27501980). It is unable to use lactose (PubMed:17056685). In vitro, shows maximal activity with o-nitrophenyl-beta-D-galactopyranoside (ONPG) and p-nitrophenyl-beta-D-galactopyranoside (PNPG) as substrates, trace activity with p-nitrophenyl-alpha-L-arabinopyranoside and o-nitrophenyl-beta-D-fucopyranoside as substrates, but no activity with p-nitrophenyl-alpha-D-galactopyranoside, p-nitrophenyl-beta-D-glucopyranoside, o-nitrophenyl-beta-D-xylopyranoside, p-nitrophenyl-beta-D-mannopyranoside or p-nitrophenyl-alpha-L-arabinofuranoside as substrates (PubMed:17056685). Hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides. Inhibited by zinc, cobalt and copper ions. Optimum pH is 6.0-6.5. Optimum temperature is 50 degrees Celsius. Thermolabile above 50 degrees Celsius. Homotrimer. Repressed by the transcriptional regulator GanR and induced by galactobiose. Also repressed by glucose. No chromogen 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) hydrolyzation. Reduces beta-galactosidase activity observed with polygalacturonic acid, citrus and apple pectins, galactan and soy flour. Belongs to the glycosyl hydrolase 42 family. Extended N-terminus. Extended N-terminus.