The molecule is a trisaccharide consisting of two beta-D-galactopyranose residues and an alpha-D-glucopyranose residue joined in sequence by (1->4) glycosidic bonds. It derives from an alpha-lactose and a beta-D-galactopyranosyl-(1->4)-beta-D-galactopyranose.
(2S,3R,4S,5R,6R)-2-[(2R,3R,4R,5R,6S)-4,5-dihydroxy-2-(hydroxymethyl)-6-[(2R,3S,4R,5R,6S)-4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxyoxan-3-yl]oxy-6-(hydroxymethyl)oxane-3,4,5-triol