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