| Oligosaccharides are the potential prebiotics,which can be degraded by the gut microbiota and participate in the regulation of the structure of gut microbiota and their metabolites,thereby improving the host health.Xanthan gum,gellan gum,curdlan and pullulan are safe food additives approved by the Food and Drug Administration(FDA),and the microbial polysaccharides derived oligosaccharides are the potential commercial oligosaccharides.The difference in glycosidic bond type and monosaccharide composition of carbohydrates showed the different fermentation characteristics.The relationships between the structure of pullulan oligosaccharides,curdlan oligosaccharides,xanthan gum oligosaccharides and gellan gum oligosaccharides and the specificity of gut microbiota regulation were remains unclear.The purpose of this study was to compare the effects of four microbial oligosaccharides on the composition and metabolites of gut microbiota to investigate their potential as prebiotics,in order to reveal the relationship between the structure of oligosaccharides and the specificity of gut microbiota regulation.Furthermore,the potential applications of microbial oligosaccharides in the regulation of type II diabetes were investigated.The main results are as follows:Microbial oligosaccharides were prepared by the hydrolysis of curdlan,pullulan,xanthan gum and gellan gum combined with ethanol precipitation,and the structure of microbial oligosaccharide were analyzed by determining the monosaccharide content,salt content,monosaccharide composition and the degree of polymerization.Curdlan oligosaccharides,xanthan gum oligosaccharides and gellan gum oligosaccharides were obtained by acid hydrolysis combined with secondary ethanol precipitation,and pullulan oligosaccharides was obtained by enzymatic hydrolysis combined with secondary ethanol precipitation.The purity of these four microbial oligosaccharides without monosaccharides is > 92%.MALDI-TOF-MS analysis showed that the degree of polymerization of curdlan oligosaccharides,pullulan oligosaccharides,xanthan gum oligosaccharides and gellan gum oligosaccharides was in the range of 2-18.Analysis of monosaccharide composition showed that curdlan oligosaccharides and pullulan oligosaccharides are composed of glucose,which is the same as the monosaccharide composition of curdlan and pullulan,respectively;xanthan gum oligosaccharides are composed of glucose,mannose and glucuronic acid,with a molar ratio of 42.72:36.73:19.47,which was similar to the monosaccharide composition and molar ratio of xanthan gum;gellan gum oligosaccharides are composed of glucose,rhamnose and glucuronic acid,with a molar ratio of 50.86:16.41:32.55,which was similar to the monosaccharide composition and molar ratio of gellan gum.The anti-digestion ability of curdlan oligosaccharides,pullulan oligosaccharides,xanthan gum oligosaccharides and gellan gum oligosaccharides was investigated by in vitro simulated saliva,gastric and small intestinal digestion,and the in vitro prebiotic properties of these oligosaccharides were investigated by cultivating Lactobacillus sp.,Bifidobacterium sp.and human fecal bacteria.Curdlan oligosaccharides,pullulan oligosaccharides,xanthan gum oligosaccharides and gellan gum oligosaccharides showed resistance to simulated saliva and gastric and small intestinal fluid and could safely reach the large intestine.Curdlan and pullulan oligosaccharides were selectively utilized by Lactobacillus and Bifidobacterium strains,resulting in enhanced bacterial growth and the production of lactic acid and acetic acid,and reduced the p H.When these microbial oligosaccharides were used for cultivating healthy human fecal bacteria,curdlan and pullulan oligosaccharides were mainly consumed over a0-12 h fermentation,which can significantly increased the production of acetic acid,propionic acid and butyric acid,and enriched genus Bifidobacterium.Xanthan gum and gellan gum oligosaccharides were mainly consumed over a 12-24 h fermentation,which can significantly increasee the production of acetic,propionic and butyric acid and the abundance of butyric acid-producing bacteria(such as Clostridia,Clostridiales,Lachnospiraceae).Compared with inulin(butyric acid production of 0.92 m M),xanthan gum and gellan gum oligosaccharide fermentation showed the highest increase in butyric acid levels,producing 3.76 m M and 3.17 m M butyric acid,respectively.Therefore,curdlan oligosaccharides,pullulan oligosaccharides,xanthan gum oligosaccharides and gellan gum oligosaccharides have the potential of prebiotics to improve human intestinal health.The specificity of microbial oligosaccharides(curdlan oligosaccharides,pullulan oligosaccharides,xanthan gum oligosaccharides and gellan gum oligosaccharides)and commonly used prebiotics(inulin and fructooligosaccharides)to regulate the gut microbiota and its metabolites was investigated by 48 h in vitro static fermentation in combination with fecal inocula from seven healthy donors and 11 patients with type II diabetes.We observed that the amount of carbohydrate utilization of microbial oligosaccharides depended on the structure of oligosaccharides and inter-individual gut microbial differences.The ability of gut microbiota to completely degrade these oligosaccharides mainly determined by the inter-individual gut microbiota differences.Compared with inulin,fructooligosaccharides,curdlan oligosaccharides and pullulan oligosaccharides,xanthan gum and gellan gum oligosaccharides fermentation was less affected by the inter-individual gut microbiota differences.Xanthan gum and gellan gum oligosaccharides consistently shaped the gut microbiota and its metabolites of type II diabetic patients,including significantly reducing the ratio of Firmicutes/Bacteroidetes;significantly increasing the relative abundance of Lachnospiraceae,Parabacteroides and Hungatella;significantly increasing the butyric acid levels and its median values were 3.8 m M and 3.1 m M,respectively.Xanthan gum and gellan gum oligosaccharides showed the good specificity in enhancing butyric acid and butyric acid-producing bacteria,which may be attribute to their shared ?(1?4)glycosidic bond.The dynamic degradation process of xanthan gum oligosaccharides and the dynamic effect of xanthan gum oligosaccharides on the gut microbiota and its metabolites was investigated by in vitro fecal fermentation with fecal inoculum from healthy donor and type II diabetic donor in dynamic gastrointestinal reactor(BGR).Xanthan gum oligosaccharides significantly improved the structure of the gut microbiota of healthy donor and type II diabetic donor after 48 h of fermentation,including the reduced ratio of Firmicutes/Bacteroidota and the increased abundance of Parabacteroides,Hungatella and UBA1819,which was similar to the result of in vitro static fecal fermentation.Xanthan gum oligosaccharides was mainly degraded during the 24-48 h fecal fermentation of healthy donor and type II diabetic donor,which significantly increased the production of acetic acid,propionic acid and butyric acid.At 48 h of fecal fermentation of healthy donor,the concentrations of acetic,propionic,and butyric acid reached 49.44,28.64,and 1.65 m M,respectively,which increased by 1.67,1.40,and 6.25 times,respectively,compared with 0 h.At 48 h of fecal fermentation of type II diabetic donor,the concentrations of acetic,propionic,and butyric acid reached 30.86,30.62,and 3.07 m M,respectively,which increased by 1.04,0.84,and 1.83 times,respectively,compared with 0 h.The greatly increased production of butyric acid was related to the increased abundance of butyric acid-related bacteria in fecal fermentation of xanthan gum and gellan gum oligosaccharides.The STZ/HFD-induced type II diabetic mice model was used to investigate the effects of xanthan gum oligosaccharides administration on glucose metabolism and gut microbiota to identify key xanthan gum oligosaccharides-responsive gut bacteria and associated metabolites involved in glucose metabolism.Xanthan gum oligosaccharides efficiently ameliorated fasting hyperglycemia,glucose tolerance,insulin levels,pro-inflammatory cytokine interleukin-6(IL-6)levels,and liver and pancreas pathological structures in T2 D mice as compared with the model group.Xanthan gum oligosaccharides shaped the colonic microbiota structures by significantly increasing Bacteroidales and Prevotellaceae UCG-001 abundance in T2 D mice.Xanthan gum oligosaccharides significantly stimulated expression of the SCFA receptors,GPR41 and GPR43 in the liver,which was associated with the SCFAs produced by gut microbiota in response to the degradation of xanthan gum oligosaccharides. |
PDF Full Text Request