Abstract
The objective of this study was to evaluate the functional properties of lactic acid bacteria (LAB) isolated from Tibetan kefir grains. Three Lactobacillus isolates identified as Lactobacillus acidophilus LA15, Lactobacillus plantarum B23 and Lactobacillus kefiri D17 that showed resistance to acid and bile salts were selected for further evaluation of their probiotic properties. The 3 selected strains expressed high in vitro adherence to Caco-2 cells. They were sensitive to gentamicin, erythromycin and chloramphenicol and resistant to vancomycin with MIC values of 26 µg/ml. All 3 strains showed potential bile salt hydrolase (BSH) activity, cholesterol assimilation and cholesterol co-precipitation ability. Additionally, the potential effect of these strains on plasma cholesterol levels was evaluated in Sprague-Dawley (SD) rats. Rats in 4 treatment groups were fed the following experimental diets for 4 weeks: a high-cholesterol diet, a high-cholesterol diet plus LA15, a high-cholesterol diet plus B23 or a high-cholesterol diet plus D17. The total cholesterol, triglyceride and low-density lipoprotein cholesterol levels in the serum were significantly (P<0.05) decreased in the LAB-treated rats compared with rats fed a high-cholesterol diet without LAB supplementation. The high-density lipoprotein cholesterol levels in groups B23 and D17 were significantly (P<0.05) higher than those in the control and LA15 groups. Additionally, both fecal cholesterol and bile acid levels were significantly (P<0.05) increased after LAB administration. Fecal lactobacilli counts were significantly (P<0.05) higher in the LAB treatment groups than in the control groups. Furthermore, the 3 strains were detected in the rat small intestine, colon and feces during the feeding trial. The bacteria levels remained high even after the LAB administration had been stopped for 2 weeks. These results suggest that these strains may be used in the future as probiotic starter cultures for manufacturing novel fermented foods.
Highlights
Tibetan kefir grains are the natural starter for fermented milk in Tibet, China
The data suggest that probiotic bacteria in the gut of kefir consumers are abundant and diverse, and microbial communities in the gut are closely correlated with health [1,2]
In the bile salts test, all of the tested isolates were able to grow in 0.3% bile, but only LA15, B23 and D17 showed resistance at a concentration of 1% bile for up to 12 h
Summary
Tibetan kefir grains are the natural starter for fermented milk in Tibet, China. The milk fermented by Tibetan kefir grains is a type of self-carbonated yogurt called Tibetan kefir, which is a traditional food of Tibetan people. Statistical data show that people who consume kefir in their diet are longevous. The data suggest that probiotic bacteria in the gut of kefir consumers are abundant and diverse, and microbial communities in the gut are closely correlated with health [1,2]. Tibetan kefir grains contain a complex microbial community composed of lactic acid bacteria (LAB) (Lactobacillus, Lactococcus and Leuconostoc) and yeasts (Saccharomyces, Kluyveromyces and Torula) [8]. Various LAB that have been isolated from Tibetan kefir grains include Lactobacillus acidophilus [9], Lactobacillus plantarum [10] and Lactobacillus kefiranofaciens [11]
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