| In this paper,the polysaccharides of Fructus Mori were studied systemically,including extraction,isolation and purification,structure characterization,antioxidant and hypoglycemic effects.The characters of the saliva,gastric and intestinal digestion,and fecal fermentation of the polysaccharide from Fructus Mori were well illustrated.And the effects of polysaccharides on the development of hyperglycemia and gut microbes in obese type diabetic mouse were also investigated.This study provided theoretical basis for improving the utilization of mulberry,and the main conclusions were summarized as following:(1)Single-factor experiment and Box-Behnken design(BBD)were applied to optimize the ultrasound-assisted extraction of mulberry fruits polysaccharides(MFP).Under optimum conditions:ratio of water to raw material 40.25:1,extraction temperature 69 °C,ultrasonic power 190 W and extraction time 75 min,the MFP yield was 3.13%± 0.07%,in accordance to the predicted value of 3.04%.The mulberry fruits polysaccharide fractions was obtained by deproteinization(MFP1),and further decolorization(MFP2).Carbohydrate content in MFP,MFP-1 and MFP-2 was 58.61%± 1.47%,69.98%± 0.91%,81.18%± 1.29%,as well as proteins was estimated 16.50%± 0.86%,1.57%± 0.63%,1.02%± 0.18%,respectively.The MFP1 exhibited the strongest antioxidant activity,while MFP2 showed the strongest hyperglycemic activity in vitro.This may be caused by their different compositions and physical properties in the three fractions.(2)The MFP was fractioned by DEAE-Sepharose fast-flow column to obtain MFP-1,MFP-2,MFP-3 and MFP-4 four fractions,which accounted for 2.74%,4.26%,15.2%and 29.4%,respectively.The carbohydrate content in MFP-1,MFP-2,MFP-3 and MFP-4 were 88.4 ± 1.34%,75.7 ± 2.67%,86.3 ± 0.57%and 81.3 ± 1.10%,and protein of 3.54 ± 0.89%,6.31 ± 0.57%,5.74 ± 1.40%and 4.11 ± 0.97%,respectively.The infrared spectrum indicated the characteristic absorption peaks of polysaccharides,and no triple-helical conformation was observed in any fractions.Scanning electron microscopy(SEM)showed smooth surface of MFP-1 and MFP-3 fractions,whereas MFP-2 and MFP-4 have pore openings and flocculent fibers on smooth surface.In addition,MFP-3 and MFP-4 showed better antioxidant activity and inhibitory effects on a-amylase and a-glucosidase compared to MFP-1 and MFP-2.(3)The MFP-3 was further purified to get a novel polysaccharide(MFP3P)with a molecular weight of 136.6 kDa composed of rhamnose,arabinose,galactose,glucose and galacturonic acid with molar ratio of 25.98%,21.51%,23.1%,13.06%and 16.35%,respectively.According to the methylation analysis,we deduced that the linkage of D-glucose was(1 ? 6),the linkage of L-arabinose was(1 ?),the linkage of L-rhamnose was(1 ? 2)and(1 ? 3),and the linkage of D-galactose was(1 ? 3),respectively.In addition,the selenide of the polysaccharide(MFP3P-Se)was obtained by the Na2SeO3/BaCl2 method with the Se content of 452 ?g/g and molecular weight of 89.1 kDa.Moreover,selenylation of polysaccharide(MFP3P-Se)greatly increased the antioxidant and hypoglycemic activities by alleviating insulin resistance,promoting ? cell mass proliferation and enhancing insulin secretion and glucose utilization.(4)The simulated saliva,gastric and intestinal digestion of polysaccharide from Fructus Mori.were investigated in vitro.It was found that the salivary amylase had no effect on the polysaccharide with molecular weight distribution of 128.7 ± 6.1 kDa,13.6 ± 1.4 kDa,and 2.9 ± 0.1 kDa.However,the molecular weight was reduced to 84.3 ± 4.7 kDa,5.2 ± 0.1 kDa,and 1.2 ± 0.1 kDa after gastric digestion,and without significant change after intestinal digestion.Meanwhile,the reducing ends were increased from 0.051 ±0.003 to 0.451 ± 0.011 mM without monosaccharide release throughout the whole digestion period,indicating that the decrease of molecular weight of polysaccharide may due to the breakdown of glycosidic bonds.In addition,when polysaccahride and lipid mixture emulsion with particle size of 74.7± 0.18 ?m and apparent viscosity of 0.132 ± 0.002 Pa.S passed through the simulated saliva,gastric and intestinal tract,the polysaccahride showed great inhibitory effect on lipid digestion.(5)The study investigated the fermentation of polysaccharide from Fructus Mori.in vitro and the contribution of its carbohydrates to the fermentation.After fermentation in human fecal cultures for 48 h,the levels of total short chain fatty acid(SCFA),acetic,propionic and butyric acids increased leading to the decrease of pH from 7.12 to 6.14.Meanwhile,the 45.36 ± 1.36%of total carbohydrate in polysaccharide was consumed,including 35.72±1.51 of arabinose,23.1 ± 1.19 of galactose,41.43 ± 1.52 of glucose,26.36± 1.93 of rhamnose,and 65.57 ± 1.07%of galacturonic aci.The increase of acetic and butyric acids productions mainly resulted from the fermentation of galactose and galacturonic acid,while the increase of propionic acid production was primarily due to the fermentation of arabinose and glucose in polysaccharide.In addition,after fermentation for 6 h,the polysaccharide had great effect on the microflora community diversity,mainly the increase of Bacteroidetes and decrease of Firmicutes.(6)Oral administration of polysaccharides from mulberry fruit Fructus Mori.(500 or 800 mg/kg/day)had significant protective effects on diabetic mice(db/db)with the following improvements:(a)significantly reduced the intake of food and water,inhibited the body weight increase,decreased the blood glucose level,and improved the glucose tolerance;(b)reduced the level of total cholesterol(TC),triacylglycerol(TG),and low density lipoprotein cholesterol(LDL-C),and increased the level of high density lipoprotein cholesterol(HDL-C);(c)significant recovery effects on organs damage including liver,kidneys and pancreas;(d)increased the enzyme activities of superoxide dismutase(SOD),glutathione peroxidase(GSH-Px)and catalase(CAT),and decreased the content of lipid peroxide malonaldehyde(MDA).In addition,the polysaccharides significantly shifted the composition of gut main microbiota with increase of Bacteroidetes and decrease of Firmicutes,Proteobacteria and Actinobacteria.Taken together,our findings suggest that the polysaccharides from mulberry fruit modulate the gut microbiota including the enhancement of functional bacteria and microbial diversity,which may contribute to the protective effects of diabetes. |
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