Substances prébiotiques et aptitudes fermentaires des bifidobactéries.

Abstract

This study focused on the in vitro and vivo prebiotic effect of different carbohydrate substrates on the development of beneficial strains such as Bifidobacterium and Lactobacillus. The in vitro experiment was run in order to test the prebiotic effect of five substrates (a whole wheat and oat bran, chicory, lactulose and pectin) and, insoluble and soluble fiber extracts of wheat and oat bran, used at 2% (P/V) as the only source of carbon on the kinetics of growth and acidification of these strains. Prebiotic activity score of the five substrates was compared to that of glucose. Results of this first experience indicate that the lactulose is the more metabolized substrate; whereas the pectin and the entire oat bran are the less metabolized, by all the tested strains. Whatever the strain used, the highest and the lowest prebiotic activity scores were those of the entire wheat bran and pectine. With an exception of pectin and, to a lesser extent, the entire oat bran, all other prebiotic substrates were able to generate lactic acid at levels varying with the used bacteria and representing 20 to 70% those registered with glucose. Growth performance of all strains on insoluble and soluble fiber extracts of wheat bran was 30% better than that on the whole wheat bran ; whereas there is no marked or improved growth registered with oat bran fiber extract or whole oat bran. These observations have led to use the whole wheat bran as prebiotic substrate for the in vivo experiment with conventional Swiss mice who, separately, received 4 beneficial strains (B.animalis subsp. lactis Bb12, B. Bifidum Bb443, Lb. acidophilus LbA-CECT478 and Lb. rhamnosus LBRE-LSAS). A series of parameters (weight of mice, implantation of the beneficial strains, impact on the intestinal flora of mice, formulation and blood counts, glycemia, proteinemia, cholesterolemia, albuminemia, prebiotic index, bacterial translocation, histology of the kidneys, liver and spleen) were evaluated after 4 weeks of experiment. The results obtained have shown that the entire wheat bran stimulates the implantation of beneficial strains, induces a reduction of aerobic and an increase of the anaerobic bacteria in the digestive tract of the mouse. There are no changes in the biochemical and haematological parameters during this experience. Histological examinations reveal the presence of inflammation and necrosis in mice fed up with Lb. Acidophilus. The immune system of the digestive tract is slightly modulated by the presence of the 3 other beneficial strains.