Ultrasound-assisted TEMPO Catalytic Preparation Of Oxidized Starch And Its Structure And Properties

In this paper,mung bean starch was used as raw material,sodium hypochlorite was used as oxidant,TEMPO（2,2,6,6-tetramethylpiperidine oxide）was used as catalyst.TEMPO catalytic oxidation method was used to prepare oxidized starch,and the process parameters were optimized to explore different ultrasonic frequency pairs.The effect of starch oxidation and its structural properties were analyzed.After sonication,the particle size was significantly reduced in addition to the properties of the original modified starch.The paper provides a new method for the preparation of oxidized starch,which provides a new idea for the deep processing of mung bean.The process parameters were optimized by orthogonal design to determine that the amount of TEMPO added was 0.1%.In the experiment of oxidized mung bean starch,the optimum process conditions were:molar ratio of oxidant 1.5:1,reaction pH 8.5±0.5,reaction time 90 min,reaction temperature 10°C;Select the optimal process conditions for orthogonal optimization to prepare ultrasonic assisted oxidized starch,the fixed ultrasonic power is 500W,select ultrasonic frequency 25 KHz,45 KHz,53 KHz,and investigate the effect of ultrasonic treatment on the preparation of oxidized starch.The results show that the ultrasonic frequency is 25 KHz.Starch has the highest degree of oxidation.The results of scanning electron microscopy showed that the original starch surface was smooth and flat,the structure was complete,the oxidized starch granules were broken,and the surface appeared porous and concave.The infrared spectrum showed that the oxidized starch showed obvious carboxyl absorption peak at around 1610 cm^-1.Starch was successfully oxidized;X-ray diffraction results showed that the oxidized starch was similar to the original starch by X-ray diffraction pattern,indicating that the oxidation was not enough to change its crystal form;the oxidized starch enthalpy increased,indicating that the starch crystal structure was not easily destroyed;After oxidation of the starch,compared with the original starch,the viscosity of the oxidized starch is significantly reduced,the particle size is reduced,and the ultrasonic assisted particle size is smaller,the solubility of the oxidized starch,the light transmittance is increased,the charge amount is increased,and the excellent properties of the oxidized starch are conducive to improving its bioavailability.