Cationic Oxidized Microporous Rice Starch: Preparation,Characterization,and Properties

In this paper,the cationic oxidized microporous rice starch was prepared using rice starch as a material,compound enzyme?glycosylase and ?-amylase were mixed in a certain proportion?as an enzymatic hydrolysis agent,sodium hypochlorite as an oxidant and3-chloro-2-hydroxypropyl trimethyl ammonium chloride?CHPTMA?as an etherification agent.In the oxidation,the effects of the oxidation time,oxidation temperature,pH and oxidant dosage on the carboxyl content?CC?of oxidized microporous rice starch were investigated.In the etherification,the effects of the etherification temperature,etherification time,etherification dosage and pH on the degree of substitution?DS?of cationic oxidized rice starch were explored.The results optimization by the oxidation response surface test showed that the optimal technological parameters for the preparing oxidized microporous rice starch were: oxidation time 2 h,oxidation temperature 45 ?,pH 9,and the sodium hypochlorite dosage was 65%.The optimization results of etherification response surface test showed that the optimum technological parameters for the preparing cationic oxidized microporous rice starch were: etherification time 13 h,etherification temperature 45 ?,pH 10.5,etherification agent dosage 8%.The effects of the enzymolysis,oxidation and cationic etherification on the blue value,retrogradation,freeze-thaw stability,acid and alkaline resistance and expansion capacity of rice starch showed that after the enzymolysis and oxidation of rice starch,its blue value increased,while the blue value decreased after the cationic etherification rice starch.The retrogradation of microporous rice starch,oxidized microporous rice starch and cationic oxidized microporous rice starch was weaker than that of rice starch.After the enzymatic hydrolysis,oxidation and etherification of rice starch,its freeze-thaw stability became worse,but its resistance to acidity and alkalinity were obviously enhanced.The influence of the enzymatic hydrolysis,oxidation and etherification on the structure and thermal properties of rice starch were studied by means of infrared spectrometer?IR?,differential scanning calorimetry?DSC?,thermogravimetric analyzer?TGA?,scanning electron microscope?SEM?,X-ray diffraction?XRD?,polarizing microscope?POM?,indicating that the polarization cross was obvious on the rice srarch granules,after the enzymatic hydrolysis,oxidation and etherification modification,the polarization cross on microporous rice starch,oxidation microporous rice starch and cationic oxidation microporous granules was still able to be observed.The crystalline structure of rice starch was a typical A-type.The enzymatic hydrolysis,oxidation and etherification could not change the crystalline structure of rice starch,that is,the derivatives of rice starch still belonged to an A-type,but affect crystallinity degree of these derivatives to some extent.The surface of rice starch was smooth,and the shape was regular.After the enzymatic hydrolysis of rice starch,the holes obviously appeared on its surface.After oxidation and etherification modification,the particle structure of derivatives was seriously destroyed,and many small pieces could be seen,and the surface of derivatives became rough,the shape was irregular.Three kinds of modification could improve the thermal properties of rice to a certain extent.The measurement of gelatinization characteristics of rice starch and its derivatives indicated that after the enzymolysis,oxidation and etherification of rice starch,its gelatinization temperature,peak viscosity,trough viscosity,final viscosity and breakdown all decreased,but the shear resistance increased.The measurement of Zn²⁺,Cu²⁺ and SO₄^2- adsorbed by oxidized microporous rice starch and cationic oxidized microporous rice starch,showed that both adsorbents could absorb the above positive and negative ions to a certain extent.