| Lactobacillus acidophilus, as one of the species naturally occurring in the gastrointestinal tract of host (human and animals), may offer various health-promoting effects (probiotic effects) to individuals by balancing the host intestinal microflore between beneficial and harmful microorganisms. Consumption of food products supplemented with the bacterium produces some claimed nutritional and health benefits including improvement of lactose intolerance, inhibition of pathogenic organisms, stimulation of immune system, reduction of serum cholesterol and suppression of tumor cells. The objectives of this study were: (1) to investigate some probiotic properties produced by the four selected strains of I. acidophilus (B, 336, Ind-1 and Lakcid) and (2) to examine their practical applications in selected dairy products.The tolerances of L. acidophilus strains to low pH of 2.5 and 1% bile salt were studied. Simulation of the gastrointestinal environments showed that after anaerobic incubation at 37癈 for 4 hrs, the survival rates of the strains ranged from 40.2% to 96.6% in pH 2.5 and from 70.0% to 97.5% in 1% bile salt solution, respectively. All the strains showed a proper resistance to the extreme stresses and perhaps survived in host intestines.L. acidophilus strain B, 336, Ind-1, and Lakcid exhibited different p-galactosidase activities. The levels of P-galactosidase released from cells varied from 0.29x10-3 U to 2.00x10-3 U, depending on the used strains which were incubated at 37癈 anaerobically for 18 hrs. The susceptibility of the four strains to antibiotics indicated that the probiotic bacterium was able to tolerate to low concentration of chloramphenicol (0.0244mg/mL~0.39mg/mL), gentamicin(31.25U-500U), penicillin(7.81U~31.24U) and rifampin(0.195ug/mL~3.12ug/mL) usually used in clinic practice. Clearly, the susceptibility of antibiotics was strain-dependent.Under anaerobic conditions with an incubation of 37癈 L. acidophilus strain B, 336, Ind-1, and Lakcid formed white precipitated-zone colonies in MRS modified medium containing bile salts plus CaCh. It meant that the probiotic bacterium had an ability toproduce bile salt hydrolase (BSH) and de-conjugate bilt salt. The higher the concentration of TDCA was in medium, the more its concentration decreased according to the studied strains. At two given TDCA concentrations 4.7069g/L and 2.2663g/L, the deconjugation rates were 72.1% to 94.9% and 30.0% to 46.6% respectively. Moreover, the strains studied showed a preference in the utilization of different forms of bile salts.The results showed that the level of serum total cholesterol decreased significantly in tested rats fed successively with high-fat feedings and supplements of L. acidophilus strains B, 336, Ind-1 and Lakcid. And the four strains showed positive effects both on the alleviation of LDL or HDL and on the reducing of RF (TC/HDL). However, no clear difference was found among these studied strains. Direct oral administration of L. acidophilus live cells to rats would produce a better effect in the reduction of cholesterol than that of acidophilus fermented milk, but they showed no significant difference.Compared to the control group, those rats consuming the supplements of L. acidophilus strain B, 336, Ind-1, and Lakcid largely increased the number of lactobacilli in their fecal samples. It further proved that L. acidophilus might survive and colonize in the intestinal tract of tested rats, showing the possibilities of its probiotic effects.L. acidophilus strain B, 336, Ind-1 and Lakcid produced 0.73%~0.78% lactic acid when incubated at 37癈 in milk for 10 hrs and coagulated milk very well. When the acidophilus fermented milks were under refrigerated storage at 4癈, the viable cells of L. acidophilus averagely were 2.9x108 cfu/mL and the viable rate varied from 87.7% to 95.9% depending on strains used. The titratable acidity of the acidophilus fermented milks increased gradually to above 1.10%. The free amino acid from the hydrolysis of milk proteins rose gradually from 120ug/...
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