Research On The Modification Of Mechanical Activation Cassava Starch And Its Properties

Mechanical activation starch(MAS),a physically modified starch,is emerged by the physically method,such as collision,shear,compression,friction,and mechanical force to change the crystal structure or the structure of some glucose units.Owing to the process of mechanical activation,the starch crystalline of starch would decrease significantly from polycrystalline to amorphous,and cold water solubility is improved.However,because of the restrictions of properties of native starch,such as low cold water solubility,poor paste stability,poor film-forming properties as well as weak emulsifying ability(EA),mechanical activation starch should be improved to meet the increasing need of industry development.This article explored the physical modification of MAS by additives and granulation,as well as the chemical modification of starch via mechanical activation solid phase esterification.The main research contents and results of this work are as follows:(1)Cassava starch was mechanically activated by a stirring ball mill,and then the mechanical activated starch was physically modified by using sucrose,maltodextrin and sucrose ester as dispersant and wetting agent.The effects of dosages of sucrose,maltodextrin,sucrose ester and particle size on the dispersion and wettability of activated starch were investigated by using caking weight and transmittance ratio as evaluation indices.The results showed that particle size in 40-60 mesh displayed good dispersing and wetting properties;sucrose,maltodextrin and sucrose ester could increase the dispersion of products apparently;the wettability of the products increased with the sucrose and maltodextrin as dispersant and wetting agent,while sucrose ester would result in a decrease of wettability.By adding sucrose 7.5%,maltodextrin 10%and sucrose ester 0.15%to activated starch,products' score reached a value of 94.90.(2)Sucrose,maltodextrin could improve the transparency and emulsifying properties markedly Meanwhile the viscosity and freeze-thaw stability were reduced.To the contrary,sucrose ester could reduce the transparency and viscosity of the products;the freeze-thaw stability and emulsification properties were increased.The results of SEM showed that the morphology particle of starch was destroyed after mechanical activation,meanwhile,activation starch composition of the skeleton by the bond of starch particle was not obvious."fixed bridge" formed amount the modified starch,led to a priority dissolution when rehydration,promoting the disperse of starch.(3)Starch stereate(SS)was producted by mechanical activation dry process with using cassava starch as raw material,NaOH as catalyst,stereate acid as esterifying agent,and self-designed stirring-type mill as solid-phase reactor.The influences of reaction temperature(Tr),reaction time(tr),dosages of esterifying agent and catalyst were investigated respectively by using Degree of substitution(DS)as evaluating index.The results showed that the optimal parameters for the preparation of starch stereate with a DS value of 0.0161 were as follow:dosage of esterifying 3.0%,tr 1.Oh,Tr 50 0C and dosage of catalyst 3.33%.(4)SS molecular groups,crystal structure and morphology were investigated by Fourier transform infrared spectroscopy(FTIR),X-Ray diffraction(XRD)and scanning electron microscopy(SEM).Moreover,freeze-thaw stability,dispersion,wettability and emulsifying properties of SS were studied too.The results of FTIR indicated that the absorption peaks of carbonyl group(C=O)appeared at 1740cm-1 in the infrared spectra of products,which suggested the generation of esterification products;XRD crystallization index revealed a destruction of starch' close lattice during the mechanical activation reaction,and the crystal structure of starch turn into an amorphous structure.The results of SEM showed that the central of starch was depressed and broken under the mechanical force,esterification reaction not only occurred on the surface of starch,but also in depth.Dispersion,freeze-thaw stability and emulsifying properties of modified stach were improved by introducing long-chain hydrophobic groups.