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

Two probiotic strains of bacteria Bifidobacterium lactis DR10 and Lactobaci llus rhamnosus DR20 were tested for their ability to utilise and grow on ga lacto-oligosaccharides present in a commercial hydrolysed lactose milk powd er. The results clearly demonstrated that B. lactis DR10 preferentially uti lises tri- and tetra-saccharides whereas Lb. rhamnosus DR20 prefers sugars with a lower degree of polymerisation, i.e., disaccharides and monosacchari des. Since galacto-oligosaccharides are non-digestible oligosaccharides, th is in vitro data suggest that galacto-oligosaccharides present in milk powd ers 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 lac tic acid bacteria, including members from the genera Bifidobacterium and La ctobacillus, were studied for their ability to utilise lactose derived olig osaccharides. A perfect correlation was observed between the ability of a s train to utilise oligosaccharide and the presence of the lactose hydrolysin g enzyme beta -galactosidase. Based on these observations, a mechanism for the utilisation of galacto-oligosaccharides in genus bifidobacteria is prop osed 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.