| A safe and cost effective approach to reduce obesity and accompanying chronic disease would be through controlling appetite and energy balance.Konjac glucomannan(KGM),a viscous soluble dietary fiber(VSDF)that hydrates gradually and develops high viscosity in solution,has been demonstrated in some preclinical and clinical studies to reduce appetite and postprandial blood glucose.The intake of KGM either as a supplement or in foods has been shown to have a weight loss effect.However,the results of randomized clinical trials have not been consistent.Besides the neglect of the correlation between its rheological properties in the digestive tract and its physiological functions,the structural elements that affect the hydration and rheological properties of KGM are not described.This may be part of the explanation for the inconsistent results.Therefore,this project was based on the analysis of the hydration and rheological properties of KGM,to study its effect on appetite and postprandial blood glucose,and evaluate its effect on long-term obesity regulation.Established the structural characteristics of KGM,which was the most effective in controlling appetite,postprandial blood glucose,and long-term weight loss.The main contents and results are as follows:Characterization of hydration and rheological properties of KGM:The straincontrolled rheometer was used to monitor the hydration and rheological properties of seven KGMs.The steady shear flow curves showed that all KGM solution presented typical yieldpseudoplastic fluid feature.In deionized water,the hydration rate and ultimate viscosity varied widely among samples(p<0.05),and this difference was also applicable to different concentration.The hydration patterns can be divided into three types,slow hydration(SH),medium hydration(MH)and fast hydration(FH),which reached a plateau after 90,15-33 and 8 min,respectively(0.5%(w/v),30 s-1,T=25?).Based on the levels of ultimate viscosity,it can be divided into high viscosity(HV),medium viscosity(MV)and low viscosity(LV),the viscosity of which was 0.89-1.30,0.79-0.82 and 0.46 Pa.s,respectively.In static simulated gastric juice(SGF),the hydration and rheological properties of KGM remained the same as in deionized water.During the dynamic in vitro digestion process,the difference in hydration and rheological properties of KGMs persisted.Among them,MHMV had a moderate hydration time.It is continuously rehydrated while being diluted by digestive juice.Its viscosity value at the end of gastric emptying was the highest among the seven samples,and the retention rate of the initial viscosity was 14%.In vivo glycemic response and appetite sensation of KGM with different hydration rate and viscosity and its in vitro digestion characteristics:Glucose solution(GS)and rice porridge(RP)were used to deliver the KGM powders with different hydration rates and ultimate viscosities(SHHV,FHHV,MHHV,MHMV).A randomized crossover trial was conducted on 16 healthy subjects,to measure changes in postprandial blood glucose and satiety.The results showed that the coordination of KGM's hydration process and gastrointestinal dilution can make MHMV(medium hydration rate and medium viscosity)achieve an optimum postprandial glycemia reducing-effect.On the other hand,FHHV and MHHV had a higher initial viscosity and provide a stronger sense of satiety.The intake of 0.75%of MHMV can reduce the area under the postprandial blood glucose curve(iAUC)of GS and RP by 33.90%and 35.30%,respectively.The dynamic digestion test of carbohydrates showed that MHMV continued to hydrate in the process of gastric juice dilution.Compared with the other three KGMs,it had a higher initial viscosity retention rate(11-13%),lower gastric emptying rate and stronger ability to retard glucose diffusion in the small intestine.The effect of long-term intake of KGM with different hydration and viscosity properties on obesity:C57BL/6J mice were used to construct obesity model,and the high fat(HF)and low fat(LF)diet mice were used as controls to explore the effect of long-term intake of KGM(SHHV,FHHV,MHHV,MHMV)on obesity.The results showed that supplementing any KGM in HF-fed mice significantly(p<0.05)reduced body weight gain.MHMV had a more gentle gastrointestinal migration rate and a higher secretion of satiety-related hormones(the secretions of GLP-1 and PYY were 1.27 and 1.16 times that of the HF group,respectively),compared with the HF group,the average daily food intake was decreased by 18.27%(p<0.05),and its final body weight was reduced by 23.31%.KGM intake maked mice have better glucose tolerance and insulin sensitivity,and can also increased the activity of antioxidant enzymes and protected the integrity of cell membranes to protect liver from HF-induced oxidative damage.KGM prevented the inflammatory response in the liver of mice by regulating liver lipid metabolism and inhibiting the production and release of inflammation-related cytokines.The histopathological results further confirmed that the intake of KGM significantly reduced the number of lipid droplets in liver cells,the inflammation of the liver lobules rarely occurred and the increase of fat cells were inhibited.Among all KGMs,MHMV had a better ability to inhibit obesity induced by HF diet and improve tissue damage and inflammation,it reduced the secretion of TNF-? and IL-6 in the liver by 25.46%and 36.09%.The weight loss mechanism analysis of KGM with different hydration and viscosity properties:through the 16S rRNA gene sequencing analysis of mice feces combined with the evaluation of the expression level of genes related to glucose and lipid metabolism,explored the effect of KGM with different hydration and viscosity properties on the intestinal microbiota and glucose and lipid metabolism.The supplementary intervention of KGM reversed the changes in the transcription levels of genes related to glucose and lipid metabolism caused by HF(p<0.05):SREBP-2,HMGCR,PPAR-?,CD11c,Leptin and Adiponectin.MHMV reduced the relative expression level of Leptin by 79.27%.The intake of KGM improved the decrease in alpha diversity caused by HF intake,improved the intestinal flora disorder caused by HF diet at the level of phyla,family,genera and OTU,and increased the abundance of dominant bacteria.It also affected the level of short-chain fatty acids.MHMV significantly reduced the ratio(F/B)of Firmicutes and Bacteroides by 65.59%(p<0.05).MHMV had the better ability to regulate the intestinal flora.Analysis of particle/molecular structure elements that cause the differential hydration and rheological properties of KGM solution:The particle structure,molecular structure,and conformation of KGM with different hydration and rheological properties were compared.The results suggested that the hydration rate and the development of solution viscosity were related to particle size and surface morphology of KGM particles rather than molecular structure.The particle size distribution value,D95,varied from 452.70 ?m to 132.30?m and the hydration time decreased from 90 min to 8 min,respectively.The combination results of small-angle X-ray scattering(SAXS)and Mark-Houwink equation,as well as differential-laser(SEC-MALS)and differential-viscosity-laser(SEC-MALS-Viscometer)suggested that KGM is a flexible random coil hydrocolloid with rigid rod segments.The molecular weight(Mw)was not the only factor that determines the viscosity of the KGM solution after full hydration.In the semi-dilute solution above the critical concentration(C*),the stronger interaction between KGM molecules maked the viscosity more concentrationdependent.At similar Mw levels,the higher main chain M/G ratio and higher acetyl content will bring higher viscosity.At the same time,the greater the proportion of the branched chain,the greater the interactions between molecules,and the higher the viscosity.MHMV had a low Mw(1.15×106 g/mol)and branch content(1.13%),a medium content of acetyl groups(2.33%)and a M/G ratio(1.48),and a medium particle size(D95=250.10 ?m),showing a moderate hydration rate(t?=33.04 min)and viscosity level(??=0.82 Pa.s),which had a more gentle gastric emptying and nutrient metabolism rate,which exhibited a better postprandial glycemia reducing and obesity suppressing effect compared with the other KGMs. |
PDF Full Text Request