Utilisation of galacto-oligosaccharides as selective substrates for growth by lactic acid bacteria including Bifidobacterium lactis DR10 and Lactobacillus rhamnosus DR20

Two probiotic strains of bacteria Bifidobacterium lactis DR10 and Lactobacillus rhamnosus DR20 were tested for their ability to utilise and grow on galacto-oligosaccharides present in a commercial hydrolysed lactose milk powder. The results clearly demonstrated that B. lactis DR10 preferentially utilises tri- and tetra-saccharides whereas Lb. rhamnosus DR20 prefers sugars with a lower degree of polymerisation, i.e., disaccharides and monosaccharides. Since galacto-oligosaccharides are non-digestible oligosaccharides, this in vitro data suggest that galacto-oligosaccharides present in milk powders are likely to promote growth of DR10 and DR20 in vivo if these strains are consumed in combination with the milk powder. Fifty four strains of lactic acid bacteria, including members from the genera Bifidobacterium and Lactobacillus, were studied for their ability to utilise lactose derived oligosaccharides. A perfect correlation was observed between the ability of a strain to utilise oligosaccharide and the presence of the lactose hydrolysing enzyme beta -galactosidase. Based on these observations, a mechanism for the utilisation of galacto-oligosaccharides in genus bifidobacteria is proposed that may help to explain the ability of these organisms to out-compete other bacteria in the ecosystcm of the human gastro-intestinal tract. (C) 2001 Elsevier Science Ltd. All rights reserved.