| The carboxymethyl starch(CMS) was prepared under the condition of using Zhongnuo 2# waxy wheat starch as material, microwave as heat resource, ethanol 95% as reaction medium and CH2ClCOOH as etherifying agent. Firstly the material was pretreated, including two steps, the separation and the purification. The waxy wheat starch was obtained, and then the property was analyzed and determined. The result showed protein content was 0.29% after purification by SDS, according with national standard GB8883-88. The samples were centrifuged at a speed of 3000r/min for 10min, and then the size distribution of the particle was analyzed by microscopy and laser particle size analyzer. The results showed that waxy wheat starch had good separation efficiency under the selected conditions in this paper. The size of large, medium and small granules was 20.1μm, 6.5μm and 4.2μm respectively of waxy wheat starch. And the moisture content was 10.9%, ash content was 0.35%, total fat content was 0.54%, crude protien content was 2.15%, fineness was 80.88% and whiteness was 89.80. The effect of microwave radiation time, ethanol volume, NaOH amount and CH2ClCOOH amount on degree of substitution was studied by the method of single factor experiment.On the basis of the experiment results, response surface methodology was conducted to optimize the technical parameters, and the optimal parameters were as follows: microwave radiation time was 2.61min, ethanol volume was 60.65 mL,NaOH amount was 4.07g,CH2ClCOOH amount was 5.09g. Under these conditions we got a degree of substitution of 0.235.The morphology was observed and the structure was confirmed by scanning electron microscope (SEM), infrared absorption (IR) and magnetic resonance spectrometer (NMR). The results showed that the surface of CMS was rough, and holes with different depth appeared on the surface. But the granules of CMS kept complete as the original starch granule. From the IR curve, the characteristic absorption peaks were observed at 1602cm-1, 1419 cm-1 and 1326 cm-1, which suggest the starch experienced carboxymethylation. According to the peak area and peak position on the NMR map, the degree of substitution was calculated basically consisting with the measured values. Rapid Visco Analyzer (RVA) and differential scanning calorimetry instrument (DSC) were used to study the gelatinization characteristic of samples with different degrees of substitution. With the degree of substitution increasing, the starting temperature of gelatinization reduced, peakviscosity, low viscosity, breakdown value, recovery value and final viscosity increasedsignificantly. DSC experiment results showed that initial temperature, end temperature andpeak temperature of CMS were little lower than that of original starch. Each parameterdecreased with the degree of substitution increasing. In addition, the characteristic of pastetransparency, freeze-thaw stability and anti-aging performance were also investigated. In all,the above-mentioned properties of CMS samples increased markedly with the increasingsubstitution level.The product was remixed with gellan gum, and then the rheological properties of thesystem were measured. And the remixed systerm was applied in making orange juice jelly.The optimum formula was obteined by orthogonal test.
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