| Konjac glucomannan?KGM?is the main component Amorphaphollus konjac.The main chain of KGM is composed of D-mannose and D-glucose connected by?-1,4linkages with a reported ratio of 1.6:1.KGM is one of the most viscous water-soluble dietary fibers known.Acetyl groups are located along the glucomannan backbone.KGM has a number of desirable nutritional and health characteristics,such as reduce weight and blood lipid,laxative,regulating blood glucose,enhance immunity,promote intestinal health,anti tumor et.al.Based on these findings,konjac gel foods made with KGM have been gaining in popularity.The production of konjac traditional foods is based on the chemical process of thermo-irreversible gel forming.In an alkaline environment,the acetyl groups of KGM are replaced by hydroxyl groups under heating,so that the main component of konjac foods is deacetylated konjac glucomannan?Da-KGM?rather than KGM.Whether the change of Da-KGM structure cause the change of its biological activity or maintain the lipid lowering as native KGM are still unknown as yet.In this paper,we taking KGM and Da-KGM as the research objects and compare the lipid-lowering effects between them.In addition,to explore lipid lowering mechanism of KGM we investigate the effects of KGM and Da-KGM on intestinal lipid absorption,intestinal fermentation,intestinal flora and gene expression.This research may provide a theoretical basis for the process of konjac healthy food.The main results were as follow.?1?Preparation and characterization and physicochemical properties of Da-KGM.Da-KGM was prepared under alkaline environment and its structure and physicochemical properties were analysised.The results showed that the characteristic absorption peak of acetyl group at 1733cm-1 was disappeared and carbonyl content decreased from 0.35%to0.09%,decreased by 74%.The internal structure of KGM from an amorphous state to a crystal structure after deacetylation.The water holding capacity of Da-KGM is 10.97±0.15g/g,compared with KGM,it had decreased by 83.7%.In addition,the high viscosity characteristic of KGM was lost after deacetylation.?2?Evaluation of lipid lowering effect of Da-KGMand KGM.To observe the effect of Da-KGM on prevention of hyperlipidemia and nonalcoholic fatty liver disease induced by high fat diet in hyperlipidemia rats,the lipid related parameters of adipose tissue,serum and liver were measured.Results showed that dietary supplementation with KGM for 10 weeks induced decreases in body weight,serum TC?46.1%?,TG?62.3%?,LDL-C?37.5%?,hepatic TC?18.9%?,hepatic TG?24.9%?,ALT?33.1%?,AST?7.23%?and MDA?17.1%?compared with the HFD group,whereas increase in hepatic SOD?18.1%?.However,Da-KGM supplementation did not exert a regulatory effect on these indexes,which indicated that the lipid lowering ability of KGM was decreased after deacetylation.?3?Analysis of the difference of lipid binding ability between Da-KGM and KGM.The effects of KGM and Da-KGM on intestinal lipid absorption were studied through in vivo and in vitro experiments.In vitro simulated digestion experiment,results showed that KGM had better adsorption capacity of fat,cholesterol and bile salt than cellulose,which boosted with the increase of sample dose and adsorption time,but both decreased after deacetylation.In vivo experiment,KGM supplementation increased fecal TC,TG and TBA excretion by 20.5%,33.34%,13.85%respectively,compared with Da-KGM supplementation.Therefore,it is likely that the difference in lipid binding between KGM and Da-KGM contributes to their different effects on blood TG and TC concentrations.?4?Study on the effect of deacetylation on the intestinal fermentation of konjac glucomannan.Results showed that the contents of SCFA were decreased with increasing deacetylation in anaerobic fermentation in vitro.Compared with3 KGM,the contents of SCFA of low deacetylated konjac glucomannan?LD-KGM?,middle deacetylated konjac glucomannan?MD-KGM?and high deacetylated konjac glucomannan?HD-KGM?were decreased by 38.3%,60.7%,62.9%respectively.Animal experiment results showed that treatment with KGM significantly increased the fecal concentrations of acetate,propionate,butyrate and total SCFA compared with the Da-KGM group.In addition,KGM also upregulate the expression of GPR41 and GPR43 mRNA.However,the ability of intestinal fermentation of Da-KGM was decreased,and the concentration of acetate,propionate,butyrateand total SCFA of Da-KGM were less than KGM.Taken together,we suggest that part of the reason for the decreased efficacy in maintaining blood lipid homeostasis of Da-KGM compared with KGM is that the fermentation characteristics of Da-KGM are changed as a result of deacetylation.?5?Effects of Da-KGM and KGM on intestinal flora.The B/E value of LD-KGM,MD-KGM and HD-KGM were decreased by 6.67%,21.8%and 14.3%respectively compared with KGM.The PI value of LD-KGM,MD-KGM and HD-KGM were also decreased by 59.2%?57.14%and 59.2%respectively compared with KGM.High throughput sequencing results showed that the effects of Da-KGM and KGM on intestinal microflora of mice fed with high-fat diet were significantly different.The diversity analysis of Alpha and Beta showed that the diversity Da-KGM group and HFD group were significantly lower than that of KGM.There were 516 OTU which both in KGM and Da-KGM group.Besides,there was 51 OTUonly in Da-KGM and 206 OTU only in the KGM group.The ratio of Bacteroidetes/Firmicutes was significantly lower in the HFD and Da-KGM group than KGM.Metastats analysis showed that at the level of family,the abundance of Bifidobacteriaceae and Lactobacillaceae in Da-KGM and HFD group was significantly lower than KGM?p<0.05?.The abundance of Bifidobacterium and Lactobacillus in the KGM group were 1.67 and 1.51 times higher than that of the Da-KGM group,and was higher than that of the HFD group by 2.15 and 1.69 times,respectively.Cluster analysis showed that the intestinal microflora of Da-KGM group was similar to that of HFD group,while the KGM group was similar to that of the control group.?6?The effect of deacetylation on molecular mechanism of lipid lowering function of KGM.The expression of CYP7A1,LDLR,SR-BI,PPAR?mRNA,SREBP1 and SREBP2protein were analyzed by RT-PCR and Western blot.Results showed that treatment with KGM increased the gene expression of CYP7A1,LDLR,PPAR?and SRBI compared with the HFD and Da-KGM groups,decreased the protein expression of SREBP1 and SREBP2?p<0.05?.Taken together,the lipid-lowering and hepatic steatosis prevention effects of KGM during high-fat feeding may be attributed to its inhibition of lipid absorption,the formation of SCFA,regulation of intestinal flora and gene of lipid metabolism.Da-KGM does not exert the same effects as KGM because of its deacetylation. |
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