| Diabetes,a metabolic disorder characterized by chronic hyperglycemia and lipid and protein metabolism disorder,is caused by insufficient insulin secretion or defective function of pancreatic islet.The incidence of diabetes is increasing year by year,which not only cause serious threat to human health,but also bring heavy economic burden to patients,families and the whole society.Dietary fiber intake has significantly negative correlation with the development of diabetes,which is also beneficial to prevent and reduce the symptoms of diabetes.Barley dietary fiber has been proved to lower blood sugar and blood lipids,exert anti-oxidative effects,and improve immunity and gut microbiota,suggesting its potential to prevent and cure chronic metabolic diseases such as diabetes and cardiovascular disease.However,the systematic research of the effects of barley dietary fiber on related metabolic syndromes still lack.In this study we took barley dietary fiber as the research object and prepared barley alkali-derived polysaccharide BIF-60,barley water-derived polysaccharide BSF-20 and BSF-80r from the enzymatically isolated fibers.The structure and solution properties of these three polysaccharides were comprehensively analyzed,which were combined with the changes of gut microbiota to further discuss the effects of barley dietary fiber on type 2 diabetic rats and the related meahanisms.The main research contents are summarized as follows:(1)Arabinoxylan(BIF-60)was isolated from BIF by ethanol precipitation at60%(v/v).BIF-60 was composed of xylose(48.5%)and arabinose(30.3%).Its average molecular weight was 1360 k Da.Methylation and 1D/2D NMR analysis showed that BIF-60 possessed?-(l?4)-xylan as backbone,comprised of un-substituted(1,4-linked?-Xylp,56.9%),mono-substituted(1,2,4-linked and 1,3,4-linked?-Xylp,22.1%)and di-substituted(1,2,3,4-lin4ked?-Xylp,18.4%)xylose units,as well as other residues(T-Araf-(1?,T-Xylp-(1?,?5)-Araf-(1?,?2)-Araf-(1?,?3)-Araf-(1?and?4)-Glcp-(1?).BIF-60 solution exhibited near-Newtonian fluid characteristics between concentrations from 0.1%to 0.5%,and exhibited shear thinning pseudoplastic fluid characteristics at higher concentrations(over 1%).In the viscoelasticity test,the storage modulus G'and loss modulus G"of BIF-60 showed frequency and concentration dependence,and BIF-60 had low gel stability and weak gelling ability.(2)Two mainly homogeneous fractions(BSF-20 and BSF-80r)were purified from BSF,and their physicochemical and structural characterization were investigated.Methylation and 1D/2D NMR experiments indicated that BSF-20 was a linear?-glucan,composed of?-D-Glcp residues via(1?4)-linkages,and occasionally single(1?3)-linkage,BSF-80r was linear?-(1?4)-glucan with similar structure characteristic as limit dextrin.The high performance size-exclusion chromatography(HPSEC)and X-ray diffraction analysis showed BSF-20 present a linear flexible chain in aqueous solution.BSF-20 exhibited high viscosity([?]=657.8 m L·g-1)in HPSEC analysis.BSF-20 solution was a typical high-viscosity plastic fluid,which exhibited shear-thinning behavior at both low and high concentrations.In the viscoelasticity test,the storage modulus G'and loss modulus G''of BSF-20 solution increased with rising concentrations,and the storage modulus G'was always greater than the loss modulus G'',showing a typical elastic gel feature.(3)In the normal rats model,the regulatory effects of BSF,BIF and BTF on blood glucose,blood lipids and gut microbiota were evaluated.All the three barley dietary fiber groups showed hypolipidemic effect,meanwhile decreased triglyceride levels,LDL-C levels,and bodyweight.For intestinal fermentation,all barley dietary fibers increased the level of isobutyric acid,isovaleric acid,valeric acidin in the ceccal content and that of acetic acid,propionic acid,and total SCFAs in feces.In addition,BSF and BTF significantly increased the cecal level of propionic acid.The gut microbiota of normal rats showed significant differences after intervention of barley dietary fibers.Among them,the structural similarity of the gut microbiota between BTF group and the normal control group was the lowest,and the diversity of gut microbiota of BIF group was higher than that of BSF group.LEf Se analysis revealed that BSF consumption could increasethe relative abundant of SCFAs-producing genus(Roseburia),while BIF promoted the that of Prevotella.(4)In the type 2 diabetic rats model,the anti-diabetic effects of BSF,BIF and BTF on type 2 diabetic rats were evaluated.All the three barley dietary fibers dsignificantly reduced FBG levels,increased HDL-C levels,reduced serum ALT levels,increased total protein levels,reduced oxidation product MDA levels,reduced creatinine levels and improved blood glucose and lipid metabolism,liver function and kidney function in type 2 diabetic rats.BSF and BTF also significantly improved insulin sensitivity in type 2 diabetic rats.For gut fermentation,BSF significantly increased the levels of butyric acid and total SCFAs in the cecal content and feces,and BSF also increased the cecal levels of propionic acid;BTF significantly increased the cecal levels of butyric acid and total SCFAs,and fecal level of acetic acid,propionic acid,and total SCFAs.BIF significantly increased the cecal levels of isobutyric acid,isovaleric acid and valeric acid as well as the fecal level of acetic acid,propionic acid,isobutyric acid,isovaleric acid and total SCFAs.The results of 16S r DNA sequencing analysis showed that the gut microbiota of diabetic rats were significantly different after intervention of barley dietary fibers.The BIF group were farthest apart from the diabetic control group,meanwhile they had the biggest difference in gut microbiota structure.Alpha diversity of BIF group(shannon and simpson index)was significantly lower than normal control group,showing the decrease of uniformity and richness in gut microbiota of BIF group.LEf Se analysis revealed that BSF consumption increased the relative abundance of Prevotella and Coprococcus,while BIF significantly enriched Akkermansia,and BTF increased that of Laospirillaceae,Lactobacillus and Allobaculum.All the three barley dietary fibers showed ameliorating effect on type 2 diabetic rats.The effects of BSF might be related to the promotion of insulin secretion,intestinal metabolite butyric acid,and gut bacterial Prevotella and Coprococcus.The effects of BIF might be related to the intestinal metabolite acetic acid,isobutyric acid and isovaleric acid,and gut bacterial Akkermansia.Regardingthe effects of BTF,it might related to the intestinal metabolite acetic acid and butyric acid,and gut bacterial Lacetospiraceae,Lactobacillus and Allobaculum. |
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