Abstract
During the past 5 decades, research in intestinal flora has made rapid progress, which includes the following: (1) development of a comprehensive culture method; (2) establishment of the classification and identification of intestinal anaerobic bacteria; (3) accumulation of microecological evidence and the beneficial and harmful functions of intestinal flora in human health. Thus it is of great importance to promote beneficial bacteria such as bifidobacteria and to suppress harmful bacteria such as clostridia among the intestinal flora. These advances in intestinal flora research are the background for the appearance of functional foods, which are classified into 3 groups based on their mechanisms of action: probiotics, prebiotics, and biogenics. Prebiotics are nondigestible food ingredients, which beneficially affect the host by selectively stimulating the growth of beneficial bacteria in the colon and/or by suppressing the growth of harmful bacteria there. The prebiotics have the potential to improve host health: The candidates are nondigestible oligosaccharides such as lactulose, stachyose, raffinose, fructo-oligosaccharides, soybean oligosaccharides, lactosucrose, galactooligosaccharides, isomalto-oligosaccharides, xylo-oligosaccharides, and palatinose. Most oligosaccharides are fermented in vitro by Bifidobacterium species (though not by B. bifidum) and to a limited degree by the Bacteroides fragilis group and Enterococcus, but they are not fermented by C. perfringens or Escherichia coli. The oral administration of oligosaccharides enhances the proliferation of intestinal bifidobacteria, improving the properties of the host's stool and scavenging the intestine, thereby altering host lipid metabolism in a beneficial way.
