Bifidogenic factors—sources, metabolism and applications

Bifidobacteria, the most predominant bacteria in the intestinal flora of infants, are established shortly after birth. Their proliferation in the lower gastrointestinal tract is stimulated by glycoprotein components of ϰ-casein in human colostrum, and, to a lesser degree, human milk. Corresponding fractions in bovine milk appear to have no stimulatory effect on the growth of bifidobacteria. As humans age, both the numbers and species of bifidobacteria which inhabit the intestinal tract change: bifidobacteria decline to the third or fourth largest group; B . infantis and B . breve are replaced with B . adolescentis while B . longum persists throughout life. This change in profile may be linked to the intake of dietary bifidogenic factors. Most animal and human diets appear to be deficient in bifidogenic factors but commerical supplements such as lactulose and fructooligo-saccharides (FOS) are now available. Lactulose is readily metabolized by bifidobacteria and some lactic acid-producing bacteria. Short-chained fructooligosacchides, commonly referred to as neosugars (with degree of polymerization (dp) of ≤6) are metabolized at somewhat lower rates than lactulose by bifidobacteria, but these sugars have advantages over lactulose insofar as clostridia and E. coli grow slowly or not at all on these FOS. Both lactulose and neosugars can be metabolized by gas-producing organisms and this has to be an area of concern for long-term administration of these bifidogenic factors. The application of bifidogenic factors to animal feeds is less problematic than human application for two reasons: animal strains of bifidobacteria can metabolize long-chained FOS (dp > 6) better than human strains of bifidobacteria; animal feeding in most cases only lasts days to a few weeks compared to decades for humans. One newly emerging bifidogenic factor, lactosucrose, is now available commerically and has shown considerable promise in terms of being readily metabolized by bifidobacteria, which in turn produce organic acids and reduce intestinal pH. Numerous other sources of bifidogenic factors have been proposed. Lactitol has no advantages over lactulose as a bifidogenic factor, while the xylooligosaccharides are both experimental and expensive at this point.