| Summary: | 碩士 === 國立臺灣大學 === 動物科學技術學研究所 === 101 === Kefir is a traditional fermented milk which originated in the Caucasus Mountains. This beverage, fermented by kefir grains, a symbiotic culture of yeasts and lactic acid bacteria, has sour, carbonated and slightly alcoholic flavor. In our previous study, we found that Hsin-Chu kefir maintained in our laboratory could lower hamsters’ total cholesterol and non-high density lipoprotein (N-HDL) cholesterol level in serum on both cholesterol-free and cholesterol-enriched diets groups. Total cholesterol concentration in liver on different diets was significantly decreased in Hsin-Chu kefir group as well. In the present study, we further screened the strains from Hsin-Chu kefir grains with high cholesterol removing abilities. The possible cholesterol removing mechanisms and potential characteristics of probiotics were also investigated.
Thirty-eight lactic acid bacteria strains were isolated from Hsin-Chu kefir grain and evaluated their cholesterol removing abilities in vitro. Three strains, 24, 26 and 30, demonstrating the highest cholesterol removing rate, were selected. We further identified the selected strains using 16S rDNA sequencing. Three strains are all Lactobacillus plantarum. For investigating the possible mechanisms, we evaluated cholesterol removing ability of resting cells（suspended in 0.85% sodium chloride solution）and dead cells（autoclaved）. Three strains in resting condition showed cholesterol removing ability, whereas, only strain 26 possessed 20% cholesterol removing ability in dead condition. The findings suggested that the cell wall binding might be one of mechanisms. Exopolysaccharide（EPS）also associated with reducing cholesterol. We then examined EPS producing abilities of the selected strains in MRS broth. The EPS levels of strains 24, 26 and 30 were 270, 268 and 231 mg/L, respectively. There are no significant differences among three strains. Additionally, for further application as probiotics, the tolerance in intestinal condition and adherence ability of the selected strains were also investigated. Results indicated the three strains possessed good bile salt tolerance. They also could survive under acid condition with about 1-2 log reduction. On the contrary, the strains didn’t demonstrated a good cell adherence ability.
In conclusion, Lactobacillus plantarum strains 24, 26 and 30 isolated from kefir grains possessed cholesterol removing abilities. Physical binding and high EPS production might be the possible mechanisms associating with this functionality. This three strains can be potential probiotics strains.
Key words: Cholesterol removing, Lactobacillus plantarum, Kefir grains, Probiotics
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