May play a role in the degradation of rhamnogalacturonan derived from plant cell walls. Hydrolysis of terminal non-reducing beta-D-galactose residues in beta-D-galactosides. Homotrimer. Up-regulated by growth on type I rhamnogalacturonan. No chromogen 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) hydrolyzation. Belongs to the glycosyl hydrolase 42 family.