Study On The Preparation, Structure And Properties Of Two Kinds Of Esterified Modified Rice Starch

Rice(a kind of Oryza) is widely planted in South China, as a predominant crop.Due to its fragility, about 15% of indica rice grains are broken during processing.Although broken indica rice has the same compositions as intact indica rice grains, it is only used as cheap food ingredients. Broken indica rice and intact indica rice have the same main components, starch(more than 80 g/100 g) and protein(about 8.8g/100 g). In order to make rational and efficient use of broken rice resource in China,the study of synthesis, structure and physicochemical properties were carried out in this thesis.Factors influencing the degree of substitution(DS) of rice starch phosphate with esterification of sodium dilydrogen phosphate dihydrate(NaH2PO4·2H2O) and anhydrous disodium hydrogen phosphate(Na2HPO4·12H2O) in the presence of urea((NH)2CO) as a catalyst were systematically investigated, which included the level of esterifying agent, reaction temperature, reaction pH, reaction time and the volume ration of the catalyst( NH)2CO. Based on above, response surface methodology was employed to optimize conditions for preparation of rice phosphate starch. The optimal reaction conditions are determined to be reaction time of 4.6 h, pH 5.5, concentration of orthophosphate salts of 46.61% of the starch mass and the amount of urea of 4.03%of the starch mass. Under these optimum conditions, the optimal DS of 0.020 34 was obtained. Compared to native starch, X-ray diffraction of starch phosphate revealed the peaks at 15°,17°,18 °and 23° were weakened somewhat, indicating the most esterification of starch occurred in the amorphous region and the damage of esterification to crystalline region was unnoticeable.The morphology was observed using a scanning electron microscope(SEM). The SEM results indicated that granules surface of starch phosphate had been eroded. Properties of rice phosphate starch,including solubility, swelling degree, pasting properties, retrogradation, freeze-thaw stability and viscoelastic properties of starch paste, were systematically studied. The results showed an increase of the solubility, swelling degree and viscosity, and a decrease of the pasting temperature, retrogradation, pasting hardness and strength.Acetylated rice starch was prepared by the reaction of native starch with acetic acid/acetic anhydride(AA) in the presence of 98%(w/v) sulfuric acid as catalyst. The effects of the amount of sulfuric acid, the level of AA, and the reaction temperature and time on the degree of substitution(DS) of acetylated indica rice starch wre investigated. Response surface analysis indicated that the optimum conditions were2.2 mL of sulfuric acid/100 g dry basis starch, 217.2 mL of AA/100 g dry basis starch,reaction temperature of 76.32oC, and reaction time of 2.55 h. Under the optimum reaction conditions, the acetylated indica rice starch with a DS of 2.45 was obtained.Various acetylated indica rice starches were characterized by FTIR, XRD and SEM.The FTIR spectrograms showed new bands at 1750, 1433, 1373, and 1239 cm-1. In the1H-NMR spectra of acetylated starch, the protons of acetyl groups appeared at1.98~2.21 ppm, and the DS of acetyalted starch calculated by 1H-NMR method was consistent with that by chemical titration, proving acetylated rice starch had been synthesized indeed. The results of XRD and SEM indicated that the structure of indica rice starch was disintegrated and a new structure of acetylated starch was formed,TG-DSC exhibited that the melting temperature of starch decreased, while the decomposition temperature of starch increased after modification. In the 1H-NMR spectra of acetylated starch, the protons of acetyl groups appeared at 1.98~2.21 ppm,and the DS of acetyalted starch calculated by1H-NMR method was consistent with that by chemical titration, proving acetylated rice starch had been synthesized indeed.The embedding and release properties of acetylated starch was determined by starch microsphere process, the result showed that embedding and release properties increased with the increasing of DS of acetylated starch.