Effect Of Microwave On The Properties Of Oxidized And Cationic Amphoteric Cassava Starch

In microwave irradiation condition, the cassava starch was modified by semidry process with the etherifying agent of3-chloro-2-hydroxypropyl-trimethyl ammoniumchloride(CHPTMA). The single factor experiments and orthogonal designs were conducted.On the basis of the single factor experiments and orthogonal designs, response surfaceexperiments were designed. The response surface experiments conducted with the fixedmicrowave power of500W, microwave time of9min and reaction temperature of80℃. Theamount of etherification agent, water content and alkali dosage were major influence factorsand the DS of cationic starch was the response value. The optimal reaction process wasconducted with starch of100g, the amount of CHPTMA6.22g, the value of n(NaOH)/n(AGU)0.22, water content22%, microwave power of500W, microwave time of9min and reactiontemperature of80℃.With cassava starch as raw material and the sodium hypochlorite as theoxidant, oxidized starch was prepared by semi dry process under microwave irradiation.Firstly, the single factor experiments and orthogonal designs were studied On the basis of thesingle factor experiments and orthogonal designs, the response surface experiments conductedwith the fixed water content of24%, reaction temperature of55℃and microwave power of500W. The major influence factors were the dosage of oxidant, pH value and microwave timeand the response value was carboxyl content. The optimal reaction process of the oxidizedstarch prepared by semi dry process and microwave irradiation were: the dosage ofoxidant(available chlorine of starch quality percentage,%)6.1%, pH value7.9, microwavetime12.2min, water content24%, reaction temperature55℃and microwave power of500W.In the preparation of amphoteric starch, cationic cassava starch of DS0.03was the rawmaterial and sodium hypochlorite was oxidant. In single factor experiments, the influenceof the parameters of every factor on both the carboxyl content and DS were discussed.Afterwards, the response experiments were conducted in the aim of learning the interaction ofvarious factors and achieving optimum process. The optimum amphoteric starch product withDS0.0291and carboxyl content0.457%when the reaction condition parameters were thedosage(available chlorine of starch quality percentage,%)6.3%, pH value of8.2, watercontent24.2%, microwave power400W, microwave time9.5min and reaction temperature50℃.The paste properties such as transparency, retrogradation, viscosity and rheology properties and paste properties of different starch products were analysed. Using laserparticle size instrument, polarizing microscope, infrared spectrometer, X-ray diffraction andelectron scanning electron microscopy, the particle size, morphology and structure of starchproducts were studied. The results showed that the transparency or freeze-thaw stability ofcationic starch and oxidized starch were better than that of original starch which wereenhanced with the increasing of DS or carboxyl content. The transparency and freeze-thawstability of amphoteric starch were better than the original starch and the cationic starch whichhad the same DS. The particle size, polarization cross, and crystalline structure of the threemodified starches mainly stayed the same with natively starch. However, introduction of newfunctional groups and particle morphology changes happened in the amorphous region duringdenaturation process in consideration of infrared spectrogram and scanning electronmicroscopy photographs.