Study On Digestion Characteristics In Vitro And Blood Lipid Regulation Effect Of Polysaccharides From Brassica Rapa L.

Tibetan turnip(Brassica rapa L.)is a biennial herb,belonging to the Brassica genus of the cruciferous family.It is mainly distributed in Tibet,Qinghai and Xinjiang in China.Turnip has been reported to have various biological functions such as anti-hypoxia and anti-fatigue.Studies have shown that turnip contains a variety of active ingredients and polysaccharide is one of the most important active ingredients.Hyperlipidemia is a common metabolic disorder in clinic.Early treatment of hyperlipidemia can effectively prevent the occurrence of metabolic disease such as obesity,hypertension,diabetes and atherosclerosis.According to the existing research,polysaccharides have a positive regulatory effect on the intestinal flora of the body,thereby regulating blood lipids.There are no in-depth studies on the effect of turnip polysaccharide on intestinal health and regulating blood lipid.In this study,the polysaccharide of turnip was prepared by the previous method.The simulated gastrointestinal digestion and fermentation experiment in vitro was used to explore the digestion and fermentation characteristics of polysaccharide from turnip.The hyperlipidemia rat model induced by highfat diets was used to explore the effect and mechanism of polysaccharide from turnip on regulating blood lipid.The main results are as follows:(1)The digestion and fermentation characteristics of polysaccharide from turnip were studied by simulating gastrointestinal digestion and fermentation experiment in vitro.The results showed that the molecular weight of polysaccharide was no significant change and it was basically not degraded.The content of SCFAs could be increased significantly after the mixed fermentation of polysaccharide and healthy human fecal flora(p<0.05).Polysaccharide of turnip could also change the diversity of human intestinal flora,such as the abundance of Fusobacteriota and Firmicutes were increased and the Actinobacteriota was decreased.In addition,the abundance of microorganisms related to metabolic disorders could be regulated by the polysaccharide,such as increasing the relative abundance of Bifidobacterium,Streptococcus and Catenibacterium,and decreasing the relative abundance of Roseburia and Phascolarctobacterium.In the metabolic pathway of starch and sucrose,the polysaccharide could up regulate the expression of 9 metabolic enzymes.(2)The hyperlipidemia rat model induced by high-fat diets was used to study the blood lipid regulation effect of the polysaccharide.After intragastric administration of the polysaccharide for 5 weeks,the body weight decreased(p<0.05)and the liver coefficient returned to normal.The results showed that the content of cholesterol,triglyceride and low density lipoprotein cholesterol in serum were reduced,and the content of inflammatory factors were also decreased significantly(p<0.05).The content of vascular cell adhesion molecule-1 and intercellular cell adhesion molecule-1 in the high-dose group(400 mg/kg/d)were also significantly different from those in the high-fat group(p<0.05).The results of liver and fat sections showed that the polysaccharide could improve the fat accumulation in liver caused by high-fat diets and reduce the size of adipocytes.In addition,the content of tight junction protein in colon tissue was increased effectively by the polysaccharide.(3)The blood lipid regulation mechanism of the polysaccharide was explored by the realtime fluorescence quantitative PCR,gas chromatography-mass spectrometry and highthroughput sequencing technology.The results showed that the content of acetic acid,propionic acid and butyric acid were increased.The ratio of Firmicutes to Bacteroidetes was also reduced significantly(p<0.05).Besides,the polysaccharide of turnip could promote the growth of beneficial bacteria,such as Blautia and Bacteroides.What’s more,the polysaccharide could significantly down regulate the mRNA expression of inflammatory factors in liver.The mRNA expression of lipid metabolism related genes such as 3-hydroxy-3-methylglutaryl-CoA reductase were returned to normal and verified by Western blot.The content of acetic acid,propionic acid and butyric acid were also increased.Besides,the ratio of Firmicutes to Bacteroidetes was reduced significantly(p<0.05).What’s more,the polysaccharide of turnip could promote the growth of beneficial bacteria,such as Blautia and Bacteroides.In conclusion,the polysaccharide of turnip could affect the composition and content of intestinal flora in hyperlipidemia rats,increase the content of SCFAs and regulate the expression of key enzymes in cholesterol and triglyceride synthesis pathway,thereby exerting the effect of regulating blood lipids.