The present invention relates to a prebiotic composition comprising a galacto oligosaccharide (GOS) produced from Lactobacillus plantarum, wherein the GOS acts as a selective growth medium for a chosen Lactobacillus plantarum probiotic bacterial strain, and wherein the GOS is substantially the same as the form produced by reverse β-galactosidase reaction in the chosen probiotic bacterial strain. The present invention also relates to methods of producing GOS and related composition incorporating the GOS.