Research On Preparation Of Porous Starch By Combined With The Freeze-thawing And Enzymatic Hydrolysis

Using corn starch as raw material,the preparation of corn porous starch was optimized by using combined with freeze-thawing and enzymatic hydrolysis process.The influencing factors and rules affecting the preparation of porous starch were discussed.The effects of freeze-thawing,enzymatic hydrolysis and combined with two methods on the morphology,microstructure and physicochemical properties of porous corn starch were investigated.The produced porous starch was used to adsorb zinc ions,starch-zinc composites were prepared in order to extend the application of starch as a nutritional enhancer.Innovative porous starch preparation process and provides theoretical and technical support for porous starch production.The paper used the oil absorption as the response value.Through Plackett-Burman and response surface optimization selected five factors which have a significant influence on the oil absorption rate,such as the enzyme hydrolysis time,pH,enzyme ratio ofα-amylase to glucoamylase,the amount of enzyme and freezing temperature.The optimum conditions of preparing corn porous starch were:enzyme hydrolysis time 11 h,pH value 4.6,enzyme ratio ofα-amylase to glucoamylase 1:3.5,the amount of enzyme 1.5%,freezing temperature-15°C.Under the optimum conditions,the oil absorption of porous starch was 126.75%.We have compared the microstructure and physicochemical properties of porous starch by freeze-thawing treated starch,enzymatic hydrolysis treated starch and combined with these two methods.Compared to native starch,the particle sizes,the crystallinity,gelatinization enthalpy of starch,the viscosity properties and rheological properties were measured.The porous starch prepared by the combined treatment has higher absorption capacities of oil and water,solubility than enzymatic hydrolysis starch.The combined treatment produced indentations,dimples and more pores in each starch granule than either individual treatment,as revealed by scanning electron microcopy（SEM）.X-ray diffraction（XRD）and differential scanning calorimetry（DSC）results showed that the starch prepared by the three treatments did not change the A-type structure,but changed the crystallinity of the starch,the crystallinity of the combined treatment was increased and the starch produce by combined treatment tolerates a higher operating temperature.The results of the rapid viscosity analysis and rheological properties showed that the starch structure was become loose and the water molecules was easy to entered after combined treatment,which is not conducive to the formation of gel elasticity and the properties of the starch solids are significant.The application of porous starch as a drug carrier was investigated.Porous starch prepared by combined treatment was used to adsorb zinc ions,the adsorption thermodynamics,adsorption kinetics and in-vitro release performances were studied.The results of adsorption thermodynamics showed that the adsorption of Zn²⁺by porous starch is more consistent with the Langmuir isotherm equation and belongs to monolayer adsorption.Adsorption kinetics studies showed that the adsorption data of porous starch on Zn²⁺is more consistent with the pseudo-second-order kinetics model.The in vitro release performance results showed that the release rate of starch-zinc composites in vitro digestion test was 94.78%and the slow release of Zn²⁺could be achieved.