Isolation And Purification Of Resistant Dextrin And Its Application In Flour Product

As a result of the improvements in living standards in modern society,a high-calorie,lowfiber diet has made chronic diseases such as diabetes,obesity,and cardiovascular disease the "number one killer" threatening human health.Resistant dextrin has good physiological functions,processing and operating characteristics.It is a new type of water-soluble dietary fiber.However,its purity is affected by the production of colored substances and small molecular impurities during the preparation process,and its application is limited.In this study,ultrafiltration and nanofiltration were utilized to remove impurities in crude resistant dextrin,and a strong basic anion exchange resin was used to decolorize the resistant dextrin.Then,its structure,basic physical and chemical properties were studied.In addition,the prebiotic effect of resistant dextrin was evaluated.The resistant dextrin was also added to flour,and its influence on flour processing quality and bread baking quality is discussed.The main research points are as follows:(1)The separation and purification of resistant dextrin was investigated using ultrafiltration and nanofiltration technologies.An ultrafiltration membrane with a cut-off molecular mass of 5 k Da was used for ultrafiltration.After ultrafiltration,the turbidity of the sample was 2.70 NTU,which was reduced by 98.06%,the absorbance was reduced by 47.26%,and the product yield was 75.34%.A nanofiltration membrane with a cut-off molecular mass of 500 Da was used to remove small molecular impurities(glucose,maltose,and salt ions).After nanofiltration,the content of glucose was 4.34%,the content of oligosaccharides with a degree of polymerization greater than 3 was 94.42%,the salt rejection rate was 95.54%,and the final product yield was 68.02%.(2)Taking the decolorization rate and recovery rate of resistant dextrin as an inspection indicator,a static adsorption experiment was conducted to compare nine anion exchange resins.The results showed that the strong basic anion exchange resin D285 had the best decolorization effect(decolorization rate and recovery rate of 84.5% and 82.8%,respectively).The decolorization conditions of D285 resin were optimized,and the best decolorization conditions were: decolorization time of 4.0 h,temperature of 35 °C,p H of 8.0,and solution concentration of 30 mg/m L.For dynamic decolorization,the decolorization and recovery rates were 86.26%and 85.23%,respectively,when the sample volume was 1.2 BV(Bed volume)and the flow rate was 1.0 BV/h.(3)The physical and chemical properties of the resistant dextrin were assessed.The content of dietary fiber in resistant dextrin was high(91.86%).The solubility of resistant dextrin was 99.14%.The hydrogen nuclear magnetic resonance showed that the resistant dextrin had?-1,2,?-1,4,?-1,6,?-1,2,?-1,4 and ?-1,6 glycosidic bonds,of which non-?-1,4 glycosidic bonds were the basis of its anti-digestibility.The infrared spectroscopy analysis showed typical polysaccharide characteristic absorption peaks.Thermal analysis showed that resistant dextrin did not have a crystal structure,and it had a fairly high stability.Scanning electron microscopy showed that the microstructure of resistant dextrin was more complex than that of ordinary starch.Resistant dextrin aqueous solution had shear thinning characteristics.The maximum degree of hydrolysis of resistant dextrin in simulated gastric juice and intestinal juice was 1.3%and 3.7%,respectively,indicating that is has good resistance to digestion.(4)Evaluation of the prebiotic effects of resistant dextrin showed that Lactobacillus casei Daitian,Lactobacillus rhamnosus GG,Bifidobacterium animalis Bb-12 and Bifidobacterium lactis Bi-07 could all use resistant dextrin for fermentation and growth.The prebiotic effect of resistant dextrin on the two lactobacillus species was not as good as galactos-oligosaccharides,but better than that of inulin and fructooligsaccharides.The prebiotic effect of resistant dextrin was not as good as galactooligosaccharides and fructoologosaccharides,but there was no significant difference compared with that of inulin.In addition,the results of the in vitro enteric fermentation process indicated that it could promote the growth of beneficial bacteria in the intestinal tract.The main short-chain fatty acids produced were acetic acid,propionic acid and butyric acid.(5)The effect of resistant dextrin on the processing quality of flour and bread was evaluated.When the addition amount was 10%(w/w),the dough formation time,stabilization time,water adsorption,and weakening were 1.88,3.21,0.79,and 0.48 times that of the flour without resistant dextrin,respectively.The maximum stretch resistance,elongation,stretch ratio,and stretch curve area of the dough showed an upward trend with the increase in the addition of resistant dextrin.Scanning electron micrograph showed that a “three-dimensional gel network structure” was formed inside the dough.Resistant dextrin could increase the elastic modulus of dough,but its effect on the viscosity modulus was not as significant as that on the elastic modulus.Resistant dextrin increased the ratio of ?-sheets in gluten protein,which enhanced the strength of gluten to a certain extent.Resistant dextrin adversely affects bread quality parameters,such as hardness.However,the results of sensory evaluation showed that the quality of bread with 2% and 4% resistant dextrin was still acceptable to consumers.