A digalactosylglycerol derivative in which the digalactosyl moiety is alpha-D-galactosyl-(1->6)-beta-D-galactosyl at O-3, with either O-1 or O-2 acylated. [Either R1 = -C(=O)R and R2 = H, or R1 = H and R2 = -C(=O)R. The molecular formula is C16H27O14R, where R represents the aliphatic group attached to the acyl carbonyl.]