Hydrolyzes melibiose, raffinose and stachyose in the following decreasing order of reactivity: raffinose, melibiose, stachyose (PubMed:12423882). Acts on both the terminal alpha-galactosyl residue and the side-chain alpha-galactosyl residue of the galactomanno-oligosaccharides (PubMed:12423882). Hydrolysis of terminal, non-reducing alpha-D-galactose residues in alpha-D-galactosides, including galactose oligosaccharides, galactomannans and galactolipids. H2O + melibiose = D-galactose + D-glucose H2O + raffinose = D-galactose + sucrose H2O + stachyose = D-galactose + raffinose alpha-D-Gal-(1->6)-beta-D-Man-(1->4)-beta-D-Man-(1->4)-D-Man + H2O = beta-D-Man-(1->4)-beta-D-Man-(1->4)-D-Man + D-galactose beta-D-Man-(1->4)-[alpha-D-Gal-(1->6)]-beta-D-Man-(1->4)-beta-D-Man-(1->4)-D-Man + H2O = beta-D-Man-(1->4)-beta-D-Man-(1->4)-beta-D-Man-(1->4)-D-Man + D-galactose 1 mM Hg(2+) and Ag(2+) decrease activity by 98% and 96%, respectively. 1 mM Para-chloromercuribenzoic acid (PCMB) completely inhibits enzymatic activity. Optimum pH is 5.0. Slowly inactivated above pH 8.0 and below pH 3. Optimum temperature is 45 degrees Celsius with p-nitrophenyl-alpha-D-galactopyranoside as substrate. Belongs to the glycosyl hydrolase 27 family.