Screening Of Cholesterol-lowering Lactic Acid Bacteria And Its Effect On High-fat Model Rats

With the improvement of people's living standard,the cardiovascular diseases caused by excessive cholesterol had seriously harmed people's health.Many studies have shown that lactic acid bacteria have the function of lowering serum cholesterol.In this paper,6 strains of lactic acid bacteria isolated from northwestern Shanxi sour porridge were research objects,and the strains with the best cholesterol lowering effect were screened out,and their effects on high-fat model rats were studied.The main contents were as follows:Firstly,the tolerance of gastrointestinal tract,determination of cholesterol lowering and primary exploration of degradation mechanism in vitro of 6 strains of lactic acid bacteria were done.(1)The results of gastrointestinal tract tolerance showed that the survival rates of 4 strains of lactic acid bacteria were over 50% after 2 hours in the MRS liquid medium at p H 3.0,and the survival rate of strain M-10 exceeded 100%.Strains M-1,M-5 and M-10 had higher tolerances to bile salts.Strain M-10 has good hydrophobicity.(2)The results of screening of cholesterol lowering in vitro demonstrated that the degradation rates of 6 strains of lactic acid bacteria were more than 50%.(3)The premiary exploration of degradation mechanism in vitro of 6 strains of lactic acid bacteria indicated that they could all reduce cholesterol under three physiological conditions: normal,dormancy and thermally lethal,and all of them could reduce cholesterol through assimilation and co-precipitation.The cholesterol degradation rates of the normal physiological strains were the highest(P < 0.05).The cholesterol degradation rate of assimilation was higher than that of co-precipitation.Among the 6 strains of lactic acid bacteria,strain M-10 in normal physiological state had the best cholesterol-lowering effect(degradation rate of 46.09%).Secondly,the culture conditions of lactic acid bacteria M-10 were optimized by single factor,Plackett-Burman(PB)experiment and response surface analysis.The optimum culture conditions of lactic acid bacteria M-10 were: glucose of 20.02 g/L,peptone of 10 g/L,manganese sulfate of 0.25 g/L,magnesium sulfate of 0.58 g/L,tween-80 of 1.9 ml/L,cholesterol micelle concentration of 0.96 mg/m L,initial medium p H of 6,liquid loading of 52.82 m L,inoculation of 2%,incubation time of 48 h,and incubation temperature of 30 ?C.Finally,the lactic acid bacteria M-10 obtained from the optimized culture was fed to the high-fat model rats and its probiotics in vivo were studied.(1)Safety evaluation results showed that lactic acid bacteria M-10 had no toxic and side effects on experimental rats,which was safe.(2)The observation of general signs of rats in the high-fat model showed that the weight gain of rats in the experimental group fed with lactic acid bacteria M-10 was significantly lower than that in the high-fat model group(P < 0.05).Results of physiological and biochemical indexes determinations demonstrated that lovastatin drugs and high dose of lactic acid bacteria M-10 liquid not only significantly reduced the contents of total cholesterol,triglyceride and low density lipoprotein in serum of high-fat model rats(P < 0.05),but also remarkably reduced the contents of total cholesterol and triglyceride in liver of high-fat model rats(P < 0.05);whereas the influences on total cholesterol and triglyceride in feces were not significant(P > 0.05).The results of this paper can not only obtain lactic acid bacteria which could effectively lower cholesterol,but also could provide theoretical basis for the northwestern of Shanxi porridge with capacity of cholesterol lowering and other functional foods.