Thesis (M.Sc.) - Cairo University - Faculty of Agriculture - Department of Dairy

The aim of this study was to select the strains with high toleration to simulate human gastrointestinal tract conditions (in vitro), survive in presence of six antibiotics, able to cholesterol assimilation (in vitro) and have the highest antimicrobial activity, among ten of bifidobacteria and leuconostoc strains, in addition to, investigate the promotion and benefit of three food substances as prebiotics for the selected strains, which used in combination as synbiotics. The cholesterol lowering properties of these synbiotics were evaluated (in vivo). Obtained results showed that 5 strains: B. adolescentis a-1, B.longum BB-536, B. longum b-1, Leuconostoc mesenteroides subsp. mesenteroides B-512f and B.bifidum Bb 12 were the most resistant to simulated gastric digestion (pH 3, pH 3+0.3% pepsin, 3% bile salts and 0.5% phenol) and showed high levels of resistance to 6 common antibiotics at the in vitro test compared to the other strains. So these strains were selected for further analyses in vitro to test their growth on prebiotic oligosaccharides, in vitro conditions. 3 strains: B. adolescentis a-1, Leuconostoc mesenteroides subsp. mesenteroides B-512f and B.bifidum Bb 12 were selected with the suitable prebiotics to form synbiotics with high ability to reduce of the lipids and cholesterol of blood serum in rats, in vivo. Also, the results showed that Bifidobacterium bifidum Bb 12 with 1% Inulin and Leuconostoc mesenteroides subsp. mesenteroides B-512f with 1% FOS were more effective for reducing serum TC, LDL-C and TG levels, as well as the atherosclerotic index, in rats fed high-cholesterol diets, and the improving the functions of liver and kidneys of these rats

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