Hydrolysis Method Influence On Structure And Properties Of Porous Starch And Its Application

Porous starch,a kind of highly promising material with the unique pore structure and high specific surface area,could widely apply to adsorption of different substances.This sample would be effectively prepared in the plant for its advantages-easily attained native corn starch,simple industrial processing,bio-enzymatic and green preparing method and broad application.In this paper,because of the good porous forming ability,corn starch was selected as the raw material.The affinity of ?-amylase and glucoamylase to corn starch was researched for preparing porous starch with better characters.The ratio of the compounded enzyme was optimized by single factor experiment.The optimal ratio,?-amylase: glucoamylase = 4:1,was determined by indexes that the hydrolysis rate,loss rate,water absorption rate and oil absorption rate was 26.26%,36.35%,56.36%,95.86%,respectively.Porous starch samples AM,AMG,and CE with the approximately same hydrolysis rate of 27% were prepared using different types of enzymes in the variable reaction time.The morphology and structural characteristics of samples were characterized by PLM,SEM,DSC,XRD,1H NMR and particle size analysis.PLM images revealed the feature of pores was tapered from the outside to the inside in the starch granule hydrolyzed by ?-amylase starch granules.However,the character of pore hydrolyzed via amyloglucosidase was inverted cone.The granular structure of compounded enzyme hydrolyzing presented the comprehensive feature of two enzymes.Compared with native starch,the polarized intensity of hydrolyzed samples obciously decreased from Polarized Light Microscope pictures.The SEM image showed the surface morphology of starch granules distributed pores with difference in depth and size,and with more uniform pore size distribution of the CE sample.Data of DSC indicated that the AM sample occupied the higheat peak temperature,therefore it probably owned a more ordered internal structure.The AMG sample had the highest gelatinization enthalpy(?H)value possibly on account of the more amylopectin in this sample.Owing to the significant reducing particle size of the AM sample,the ?-amylase tended to break starch granules.Amyloglucosidase probably prefered to hydrolyze smaller particles for the decreasing small size particle distribution after enzymatic recation.The material left behind after enzyme treatment was then treated to thermal analysis using DSC to characterize the hydrolysis product.The result of XRD manifested that enzymatic hydrolysis could increase the relative crystallinity of the enzymatic starch,which was likely to explain the hydrolysis mainly located on the amorphous region.NMR results stated the decreasing DB value,the rising relative content of the ?-1,6 glycosidic bond of the AM sample.It was proved to be a truth that the ?-amylase acted much more on the amylose.The sample hydrolyzed by ?-amylase showed a characteristic peak at the position of 4.31 ppm of the spectrum signal,but this signal fail to present in native starch and AMG sample.It means the signal could provide a basic method for distinguishing the type of hydrolysis enzyme.The adsorption kinetic curves of methylene blue in were more consistent with he quasi-second-order kinetic model due to methylene blue mainly distributing on the surface of starch granules.Enzymatic starches with a significantly increasing adsorption of methylene blue had more surface area than native starch.Taking use of ethanol as solvent to prepare the embedded mixture of porous starch and vitamin E,the CE-VE sample had the highest embedding rate and the retention rate reached 60%.The viscous vitamin E adhered to the suface of native starch paticles whereas it was absorbed into the porous starch paticle illustrated from the appearance of SEM images.CLSM pictures distinctly replied the inside distribution of VE in the starch particle.There was only a little VE in the native starch but full of it in porous starch samples.The relative crystallinity results of XRD obviously indicated the porous starch prepared by the compound enzyme could adsorb more VE,and the larger cavity structure of the granules was more favorable for the loading.To some extent,porous starch could delay the oxidation of VE under conditions of avoiding light,avoiding oxygen and nature.The retention rate of CE-VE sample placed in natural condition was half of the original embedding rate after 21 days.In the process of simulating digestion in vitro,AM-VE and CE-VE began to produce reducing sugar in the oral cavity.AMG-VE and NS-VE produced reducing sugar from the intestine for its more stable crystal structure.In vitro release of vitamin E,NS-VE and AMG-VE started to release in the stomach,because more VE was attached to the surface of the particles,AM-VE and CE-VE released less in the stomach and intestine.The porous starch protected vitamin E during the digestion process,but it failed to completely release in simulate intestine fluid.