Study On The Prebiotic Mechanism Of Food-derived Polysaccharides Based On The Regulation Of Gut Microbiota

Polysaccharide is the main active component of many natural products,which has the functions of immune regulation,anti-tumor,anti-oxidation etc.Among them,food-derived polysaccharides are the research hotspot in recent years,including animal polysaccharides,plant polysaccharides,fungal polysaccharides and so on.However,as a high molecular polymer,some polysaccharides can not be directly degraded and utilized by human cells after oral administration.They can be catabolized by gut microbiota and regulate the composition of gut microbiota,which is closely related to their physiological functions.This study is represented by Hericium erinaceus polysaccharide(HEP),Lycium barbarum polysaccharide(LBP)and Hyaluronic acid(HA).To explored the digestive characteristics of different food-derived polysaccharides and their interaction with gut microbiota by using in vitro gastrointestinal digestion model,fecal bacteria fermentation model and 16 S r RNA gene amplicon sequencing analysis.The specific research results are as follows:(1)Purification and structural characterization of HEP.HEP was isolated and purified from crude extracts of Hericium erinaceus mycelium by AKTA protein purification system.The average molecular weight of HEP was about 16 k Da measured by high performance gel permeation chromatography(HPGPC).In the solution,Congo red assay indicated HEP had a triple-helix structure.The mass percentage of monosaccharide composition was glucose84.36%,galactose 7.11%,mannose 0.91%,fucose 0.85%,Arabia sugar 5.11%,xylose 1.05%,rhamnose 0.62%.The infrared spectrum shows that HEP is a kind of pyranose.(2)Simulated gastrointestinal digestion of food-derived polysaccharides.The reducing sugar content of HEP increased after simulated digestion,from 0.084 ± 0.017 mg/m L to 0.256± 0.051 mg/m L at the end of the gastric phase,and from 0.360 ± 0.072 mg/m L at the end of the intestinal phase.The molecular weight of HEP before the simulated digestion experiment was16 k Da,which was reduced to about 5 k Da at the end of the gastric phase and about 480 Da after small intestinal digestions.The results showed that the sugar chain of purified HEP was broken,reduces molecular weight and becomes oligosaccharide fragments after gastrointestinal digestion in vitro.he product of digested HEP(HEP-D)were isolated and purified for further study.The molecular weight of LBP after in vitro gastrointestinal digestion is still about 20 k Da.The molecular weight of five different HA(HA-1,HA-2,HA-3,HA-4 and HA-5)after in vitro gastrointestinal digestion kept stable,which were about 2.5k Da,120 k Da,240 k Da,480 k Da and 1000 k Da respectively.These results indicated d that LBP and HA are indigestible in simulated gastrointestinal digestion.(3)Determination of antioxidant capacity of food-derived polysaccharides in vitro.HEPD enhanced the reducing power,the ABTS free radical and superoxide anion free radical scavenging activities,almost unchanged the hydroxyl free radical scavenging activity,but weakened the DPPH free radical scavenging activity.The total reducing power,ABTS,DPPH,superoxide anion,and hydroxyl radical scavenging activities of LBP increased with concentration,showing concentration dependent effect.The antioxidant capacity of HA is related to molecular weight.The lower molecular weight HA had better antioxidant activity.(4)Interaction between food-derived polysaccharides and gut microbiota.Fecal seeds from six healthy volunteers were subjected to anaerobic fermentation in vitro of separate and mixed samples.The structure and function of gut microbiota after fermentation of polysaccharides were analyzed by 16 S r RNA gene high-throughput sequencing analysis.We found HEP-D significantly increased the richness and diversity of gut microbiota.The biomarkers of HEP-D were Lactobacillus and Bifidobacterium by Lefse(linear discriminant analysis effect size)analysis.The functions of lipid metabolism,digestive system,energy metabolism,and a series of pathways related to glucose metabolism were up-regulated in HEPD groups by PICRUSt2 analysis.LBP can significantly change the structure and function of the human gut microbiota,improve the abundance of probiotics such as lactobacillus,Bifidobacterium,and Bacteroides in gut microbiota,and up-regulate the related pathways of lipid metabolism and digestive system.Different molecular weights of HA have different effects on gut microbiota.The main up-regulated gut microbes were Lactobacillus and Bifidobacterium.The relative abundance of Ruminococcus and Blautia have a positive correlation with the molecular weight of HA,while Megamonas has a negative correlation.The different molecular weights of HA all can up-regulated the digestive system.The short chain fatty acids(SCFAs)in the anaerobic fermentation broth in vitro were determined by ultra-high performance liquid chromatography.The results showed that HEP-D,LBP and HA all promoted the production of SCFAs.