| Purple yam,which belongs to the species of Dioscorea alata L.,is characterized by its color and anthocyanins that exhibit a strong antioxidant activity.The content of starch in purple yam is approximately 16?20%of the total biomass.Purple yam was chosen as raw material in this paper,the autoclaving treatment,enzyme-autoclaving treatment,and double enzyme purification treatment were used to prepare purple yam resistant starch.The some modern analytical testing technologies were taken to analysize the structural characteristics and physicochemical property of purple yam resistant starch.On the basis,the in vitro experiment was conducted to investigate the effect of purple yam resistant starch on the proliferation of bifidobacteria,and the survival rate of bifidobacteria in simulated gastrointestinal tract conditions were also researched to demonstrate the relationship between structure and prebiotics efficacy.After that,the effects of resistant starch on the lipid metabolism and intestinal microflora of high-fat hamsters were studied by animal experiment.The relationship between lipid metabolism and intestinal microflora was analyzed.The results were concluded as follows:1.The effect of starch concentration,dosage of pullulanase,enzyme digestion time and autoclaving time on the yield of purple yam resistant starch prepared by enzyme-autoclaving method were studied and optimized through orthogonal tests and variance analysis.The hydrolysis kinetics of resistant starch produced by gelatinate,autoclave and enzyme-autoclaving method were compared and analyzed.The results showed that the content of resistant starch increased first and then decreased with the increase of the factor levels.The optimum preparation conditions of purple yam resistant starch were starch concentration of 20%,pullulanase dosage of 8 U/g,enzyme digestion time of 12 h,two autoclaving-cooling cycles(120?/40 min).Purity,yield of resistant starch were 96.67%and 47.85%,respectively.Hydrolysis properties experiments showed that the hydrolysis rate,hydrolysis index and estimated glycemic index of resistant starch prepared by enzyme-autoclaving method significantly decreased and had better digestion resistibility when compared to gelatinized and autoclaved starches.2.Resistant starch(RS)was prepared from purple yam starch by autoclaving-cooling cycles(DAS)coupled with pullulanase debranching(PDS).On that basis,PDS and DAS were extensively hydrolyzed by thermostable ?-amylase and amyloglucosidase to obtain PDS.H and DAS.H,showing a much more favorable treatment in RS preparation to increase the RS yield.Differences in structural characteristics and in vitro digestibility were investigated.The result showed that granule of RS exhibited rough surface and irregular shape.DAS had the lowest amylose content(29.52%),whereas PDS.H had the highest(41.96%).The order of crystallinities of RS was PDS.H(31.23%)>DAS.H(30.16%)>PDS(21.23%)>DAS(15.30%).PDS.H had the highest gelatinization temperature and melting enthalpy(?H),whereas DAS had the lowest values.Analysis by digestibility in vitro indicated a decreased hydrolysis index and glycemic index for decrease in swelling power and water-binding capacity,and the more well-ordered double helix structure and crystallization in PDS.H than in the three other RS.Results suggest that starch which subjected to autoclaving-retrogradation combined pullulanase debranching and double enzymes hydrolysis might have more advantages over the other treatments such as lower water-holding capacity and freeze-thaw stability,higher gelatinization temperature and gelatinization enthalpy,and more ordered internal crystal structure.3.The in vitro prebiotic effects of RS prepared by different treatments from purple yam on Bifidobacterium adolescentis(bifidobacteria in short),were investigated.Tolerance test indicated that bifidobacteria in the PDS and PDS.H media adapted better to simulated upper gastrointestinal conditions(at pH 1.5?3.0;0.3%and 1.0%of bile acid)than in the GLU(glucose)and DAS media.PDS.H with highest digestion resistibility exhibited significant effects on OD600nm value(1.544)and pH value(4.21),when the carbohydrate concentration was 20 g L-1.Additionally,the exponential growth phase of bifidobacteria was 2 h in the medium with PDS or PDS.H,whereas it was 4 h in the medium with GLU or DAS.A higher content of short-chain fatty acids(SCFAs)was obtained in the PDS.H medium.Analysis on the structural features of RS and fermented RS indicated that PDS,especially PDS.H,had the rougher surface and higher crystallinity than DAS.Fermented RS at simulated large bowel environment showed the eroded surface and decreased crystallinity.All these findings suggest that RS with rough surface and perfect crystalline structure providing the better adhesive conditions and growth substrate could protect bifidobacteria from gastrointestinal conditions and enhance the proliferation of bifidobacteria.4.This study investigated the interventional effect of resistant starch(PDS.H)from purple yam(Dioscorea alata L.)on regulating lipid metabolism and gut microbiota in high-fat diet fed hamsters.Compared to low levels of RS(LR)treatment,high dosage of RS(HR)administration of hamsters showed more efficiently in controlling body weight and adipose tissue mass,together with an increased HDL-C concentration and decreased triglyceride(TG),total cholesterol(TC)and LDL-C concentrations.The histomorphological analysis of liver,cecum and colon indicated an amelioration of chronic inflammation after RS administration.Furthermore,molecular analysis of the hamsters' fecal bacteria populations by 16S rDNA gene PCR amplification and sequencing revealed that the improvement of TG and TC which induced through feeding RS in the hyperlipidemic hamsters was strongly associated with alterations of the gut microbiota.Bifidobacteria and Lactobacillus,after feeding with RS,could be found increased dramatically and highly correlated with blood lipid levels specifically at high doses,and was positively related to the level of HDL-C and negatively correlated with TG,TC and LDL-C.These results may be explained by the fact that dietary RS accordingly affected lipid metabolism in vivo,through a favorable effect on the gut microbiota. |
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