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14 lactic acid bacteria selected from koumiss in Urumqi,Xinjiang and Yili areas,were used in the experiment of studying the ability to degrade cholesterol.Five strains A1,B3, H1,H3 and S1 of them have relatively high degradation ability,and in conventional physiological and biochemical tests,they are initially identified to be lactic acid bacteria Meanwhile,simulation experiments in vitro to the five strains were carried out,including acid resistance experiment at pH value of 1,2 and 3;osmotic resistance test under different NaCl concentration of 3%,4%and 5%;bile tolerance test under the conditions of cow bile salt concentration at 0.10%,0.15%and 0.20%.At pH value of 3,in the first 12h,the OD values all had a great increase.The strains grow in the logarithmic phase,cell concentration of which is greater than 4 times just when inoculated,and the osmotic pressure resistance is inversely proportional to osmotic pressure(NaCl%).Strains A3,H2 have shown strong anti-osmotic pressure ability,in the first 24h with control.In the bile tolerance test,five strains begin to show tolerance in 12 hours.Strains A3,H2 show a strong bile tolerance at 0.20%bile salt concentration.On the basis of traditional biochemical identification,five strains A1,B3,H1,H3and S1 were tested for 16S rDNA gene amplification and sequencing by molecular biological methods.The results are compared with the standard strains of Lactobacillus 16S rRNA/ DNA sequences for homology analysis,establishing the phylogenetic tree.It was shown that strains A1,B3 and H3 have a 100%homology with the standard strains of Lactobacillus fermentation LB21.while strains H1 and S1 have a 100%homology with the standard strains of Lactobacillus casei MCRF-284.By phylogenetic tree analysis and 16S rDNA sequence analysis.The strains A1 and B3 and H3 can be identified as Lactobacillus fermentation,and the strains H1 and S1 are identified as Lactobacillus casei.The initial and practical research of cholesterol degradation mechanism of identified strains A1、B3、H1、H3 and S1 showed that the cholesterol removal rate was highest under the condition of cow bile salt concentration of 0.20%,while strains H1 and S1 of 0.10%.By the means of ultrasonic wave changing the permeability of cells,in the power of 600w under the conditions of ultrasound for 3s,5s interval,49 cycles,3 times to repeat,we detected content changes of cholesterol in fermentation broth and found that there are different extents of growth,which means that part of intracellular cholesterol has been released.It can be initially inferred that the strains absorb cholesterol.In the research of cholesterol degradation ability in food trends,under the same fermentation conditions basically,it was found that strain A1 has the largest degradation rate in the first 48h in the degradation of egg-yolk cholesterol;strain H1 in the first 24h in the degradation of liver cholesterol;H3 strain in the first 24h in the degradation of brain cholesterol.
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