Screening And Primary Study Of Lactic Acid Bacterial For Cholesterol-Degrading

With the rapid improvement of living standard and constantly changing of dietetic structure, ingestion of excessive cholesterol causing hypercholesterolemia, as well as cardiovascular disease and atherosclerosis, has been threatening the human health seriously Recently, much attention has been paid to the study about reducing daily intake of cholesterol and plasma cholesterol. This paper has studied the screening of high efficiency and safety cholesterol-degrading lactic acid bacteria from food related products and provided theoretical basis for the lactic bacteria acid preparation and the mechanisms of cholesterol removal. The main results includes:More than 100 strains of lactic bacteria acid were isolated form fermented foods, such as ham, yogurt, and pickled vegetables. The quantity of the cholesterol-degrading in MRS-CHOL medium was used to analyze their cholesterol-reducing ability. As a result,31 strains showed cholesterol-degrading ability. The results of stability and efficient of cholesterol removal showed that strains of JH-1, P9, NL3 were selected as testing target for their excellent cholesterol-reducing ability. Based on the studies including morphological, physiological and biochemical characteristics,16S rDNA sequence analysis and phylogenic analysis, the lactic acid bacteria JH-1, P9, NL3 were identified as Lactobacillus brevis, Lactobacillus rhamnosus and Lactococcus lactis subsp. lactis, respectively. The 16S rDNA sequence of the strain JH-1 is a 1446 bp DNA fragment, which has been submitted to the NCBI GenBank(FJ824740.1).Studies on the ability of acid tolerance, the effect of cholesterol-degrading of bile salt and antimicrobial activities of the strain JH-1, P9, NL3 were demonstrated. Strain JH-1 survived at pH 2 after 3 h culture and the living bacterial number could reach 108 cfu/mL. Growing with or without bile salt, cholesterol-degrading of the strain of JH-1 and P9 were similar from each other. Strain NL3 grown without bile salts removed very little cholesterol from medium. Three strains showed different antimicrobial activities. Lactobacillus rhamnosus, P9 showed strong antibacterial activity to Bacillus cereus, Staphylococcus aureus and Micrococcus luteus. Take into account for the advantage of Lactobacillus brevis JH-1,it could be futher studied as potential cholesterol degrading strain.The effect of various on degradation rate of cholesterol by Lactobacillus brevis JH-1 was studied. On the basis of single factor experiments, the optimal conditions for liquid fermentation was found to be:cholesterol 0.5 mg/mL, Tween-80 2 m L/L, glucose 17.5 g/L, peptone 10 g/L. The effect of cultivation temperature, initial pH of the media, cultivation time, inoculation percentage were studied on the growth of Lactobacillus brevis JH-1, and the optimal fermentation condition was obtained as follow:37℃, pH 7,48 h,2% respectiviely. After the optimization test, the degradation rate of cholesterol was 70.15%.Studies on the mechanisms of the cholesterol-degrading ability of Lactobacillus brevis JH-1 includes:analysis of cholesterol assimilation and cholesterol co-precipitation, cells resistance to lysis by ultrasonic. The results indicated that, assimilation contributed to the reduction of cholesterol by Lactobacillus brevis JH-1 in vitro.