Study On The Effect And Mechanism Of Lactic Acid Bacteria Fermented Milk Assisting In Lowering Blood Lipids

Lactic acid bacteria(LAB)have been the research hotspot owing to the functions of reducing serum lipid and preventing fat accumulation.Based on the In vitro screening model for serum lipid-lowering function,some LAB owning the proprietary intellectual property rights have been isolated from the intestinal tract of long-living population during the recent 10 years.In this work,by the in vitro and in vivo experiments,the ability of serum lipid-reducing of the Lactobacillus rhamnosus LV108,Lactobacillus casei grx12,Lactobacillus fermentum grx08 and the mixed strains of these three strains were systematically evaluated.Moreover,the mechanism of serum lipid-reducing of the milk separately fermented with L.rhamnosus LV108 and the mixed strains were researched at the level of intestinal flora and serum lipid metabolism related genes transcription,respectively.The results were as follows:1.Selection of LAB from long-living people and preparation of fermented milk with high viable countsThe faecal samples of long-living people were collected and more than 3100 LAB were isolated.Considering the experiment results of safety,function and processing property,L rhamnosus LV108,L.casei grx12 and L.fermentum grx08 were selected for the excellent processing property,antioxidant function and cholesterol-lowering ability.These three LAB were used in the next experiments.The high viable count of LAB in the fermented milk is the basic condition to play the probiotic role in the gut.However,there are certain defects in the texture and flavor of the products using probiotics as the starter By orthogonal test,the optimal conditions for the L.rhamnosus LV108 fermented milk were:inoculation quantity 4.0%,sucrose 7.0%,39℃ and milk solid content 14.0%.Meanwhile,the optimal conditions for the mixed strains fermented milk were:inoculation quantity 5.0%,sucrose 8.0%,37℃ and milk solid content 12.0%.Moreover,the properties of the flavor,texture and storage were verified.The viable counts of the LAB were higher than 1 x 108 CFU·mL-1 on the 21st day of storage in these two kinds of fermented milk.2.Cholesterol-reducing ability of the single strain and the mixed LAB tested in vitro.The LAB could reduce the Cholesterol level as the chelating agent of bile acid which is the important biological foundation to reduce the serum lipid for the LAB.The cholesterol-lowering ability of the L.rhamnosus LV108,L.casei grx12,L.fermentum grx08 and the mixed LAB(these three strains mixed with the ratio of 2:1:1)were researched in vitro.The cholesterol-lowering ability of the L.rhamnosus LV108 was similar as the mixed LAB while significant higher than L.casei grx12 and L.fermentum grx08 in the later period of fermentation.The degradation rate of cholesterol for L.rhamnosus LV108,L casei grx12,L.fermentum grx08 and the mixed LAB was separately 51.93%、38.79%,38.20%and 47.11%at 24 h.Furthermore,the superiority of L.rhamnosus LV108 and the mixed LAB in lowing cholesterol level was obvious at the stage of fermentation later than 20h,indicating that long period fermentation give full play to degrade cholesterol.The retention time of the LAB colonized in the gut was very important for cholesterol degradation.Moreover,cholesterol could induce the LAB to degrade cholesterol.The limiting degradation concentration of cholesterol for L.casei grx 12 and L fermentum grx08 was very low.As the cholesterol reaching to 1.25 mg·mL-1,the growth of L casei grx12 and L.fermentum grx08 could be inhibited while the cholesterol-lowering ability of L.rhamnosus LV108 and the mixed LAB were 2.15-fold higher than L.fermentum grx08.Glucose,bile salt and pH could improve the cholesterol-lowering ability as well as inhibit growth.The three LAB and the mixed strain presented optimal cholesterol-lowering ability when the glucose concentration,bile salt concentration and pH was separately 0.2%-0.3%,2%and 4.5-5.5.Furthermore,the three single strains and the mixed LAB could assimilate and precipitate the cholesterol.The cholesterol was demonstrated to be permeated into the cytomembrane by ultrasonic resistance test,and the permeated cholesterol was taken into the assimilate process.The cholesterol precipitating property was showed no significant difference between L rhamnosus LV108 and L.casei grx 12 and L.fermentum grx08.The outstanding cholesterol-reducing ability of the L rhamnosus LV108 might be ascribed to its strong assimilation capacity.3 Hypolipidemic effect of fermented milk containing single or mixed lactic acid bacteriaHypolipidemic effect of fermented milk containing L rhamnosus LV108 or mixed LAB was investigated by using hyperlipemic rat model.As results,intervention with fermented milk could decrease the level of TG and TC in serum,liver and small intestine of the hyperlipemic rat of which the liver index,body fat index and body weight increment were abated.What’s more,less fat accumulated in the liver and more TG,TC and TBA appeared in the feces of the intervention group.These results suggested that fermented milk containing L.rhamnosus LV108 or mixed lactic acid bacteria could ameliorate the hyperlipemia of rat by reducing absorption of TC and TG and increasing excretion and synthesis of bile salt,eventually relieving accumulation of fat in liver and body.Interestingly,though the ability to remove TC in vitro of L rhamnosus LV108 was stronger than that of mixed strains,the hypolipidemic effect of fermented milk containing single or mixed strains was almost the same4 Hypolipidemic mechanism of fermented milk containing single or mixed lactic acid bacteriaHypolipidemic mechanism of fermented milk containing L.rhamnosus LV108 or mixed LAB was comparatively investigated by measuring the lipid metabolism genes’ transcription and intestinal flora of hyperlipemic rat model.Both L.rhamnosus LV108 and mixed strains fermented milks could up regulate the transcription of genes on LXRs axis,promoting reverse cholesterol transport to enteric cavity and limiting the absorption of TC.The up regulation ability to LXRs axis genes of L.rhamnosus LV108 fermented milk was stronger than that of mixed strains fermented milk.Furthermore,AMPK pathway was not activated by L.rhamnosus LV108 and mixed strains fermented milk,but the transcription of PPARa was obviously up regulated.weakening the level of TG.Interestingly,the fat synthesis gene down regulation ability of mixed strains fermented milk was stronger,and mixed strains fermented milk possessed stronger recovery ability to intestinal flora,which clarified why the hypolipidemic effect of fermented milk containing single or mixed strains was equivalent.In summary,human source lactic acid bacteria fermented milk could improve intestinal flora and regulate the transcription of lipid metabolism genes,thus reducing absorption and synthesis of TC and TG,increasing reverse cholesterol transport,eventually ameliorating hyperlipemia.