Cell-free wheys from bifidobacteria fermented milks exert a regulatory effect on the intestinal microflora of mice and humans.
Bacteroides fragilis and clostridia are normally present in the human colon but they may exert pathogenic effects when the homeostasis is upset following various forms of stress. One approach to preventing gastrointestinal disorders is to use bifidobacteria fermented milk. It has been suggested that the efficacy of such a product is related to abiotic compounds produced during milk fermentation. Experiments reported in this paper attempt to check this theory. Six whey retentates were prepared by fermenting cow's milk with six human strains of Bifidobacterium breve and acetic and lactic acids were eliminated by ultrafiltration. Their ability to reduce intestinal clostridial carriage was assessed in C3H mice. Only one whey retentate led to a decrease in clostridia, bacilli, B. fragilis and fecal pH and to an increase in bifidobacteria. Assays in ten human volunteers resulted in similar changes in fecal flora and fecal pH within 7 days of whey retentate intake (30 mL/day). No antibiotic-like effect was demonstrated in vitro. Compounds involved in microflora regulation were located in two ultrafiltrated fractions (30-100 and 100-300 kDa). Both fractions contained mainly low molecular weight glycoproteins (20-40 kDa) and two high molecular weight glycoproteins (121, 211 kDa) that were almost undetectable in the inactive 10-30 kDa fraction.