Best Answer: β-galactosidase is a hydrolase enzyme that catalyzes the hydrolysis of β-galactosides into monosaccharides. A β-galactoside is a type of sugar in which the glycosidic bond lies above the plane of the galactose residue. The most commonly recognized and used β-galactoside in biochemistry is Lactose. Found everwhere from E.coli to plants to humans. Source(s): http://en.wikipedia.org/wiki/Beta-galact...