| In recent years, waxy rice starch with good properties, such as high freeze-thaw stability, creamy fat-like mouthfeel, highly digestible, low-calorie and hypoallergenic, has become a focus in the starch research and application field.Firstly, it was studied in this dissertation how to prepare the hydroxypropylated, acetylated and acetylated hydroxypropyl waxy rice starch, and what the optimum conditions for production of them were. Secondly, the physicochemical properties, especially retrogradation property of the native waxy rice starch and the modified starch above, were investigated by Scanning Electron Microscope (SEM), X-Ray Diffractometer, Rapid Viscocity Analyzer (RVA) and Differential Scanning Calorimeter (DSC). Finally, the quality of waxy rice cake was improved by addition of hydroxypropylated waxy rice starch.Taking waxy rice starch as raw material, on account of the extent of substitution for food grade, the optimum conditions for hydroxypropylation were as follow: the ratio of starch to propylene oxide 25:4 (w/v), sodium hydroxide 1.2% (w/w), reaction temperature 45℃, starch slurry 40%, reaction time 16 h. The optimum conditions for acetylation were as follow: the ratio of starch to anhydride 12.5:1(w/v), pH 8.5, reaction temperature 25℃, starch slurry 40%, reaction time 1 h. The production of acetylated hydroxypropyl waxy rice starch was done by acetylation of hydroxypropylated starch on the condition above.The chemical treatment of waxy rice starch with propylene oxide or acetic anhydride resulted in changes of starch granule structure. The X-ray diffraction patterns showed the characteristics of A-type in both native and modified waxy rice starch. Modified starches had lower gelatinization parameters (To, Tp, Tc and△H) than those of native starch by using Differential Scanning Calorimeter (DSC). Rapid Visco Analyzer (RVA) showed that pasting temperature of modified starch decreased, whereas peak viscosity increased compared to the native starch. The addition of NaCl, citric acid and sucrose all improved the clarity of paste.The anti-retrogradation property of modified waxy rice starch improved compared to the native starch. The anti-retrogradation property was increased in the order: native starch< acetylated starch < hydroxypropylated starch < acetylated hydroxypropyl starch. With the increase of the extent of substitution (DS or MS), the△H_r and ratio of the retrogradation decreased. The absorbance of starch was increased as the storage time prolonged. The native starch had the highest value of△H_r, ratio of the retrogradation, and absorbance. The freeze-thaw stability was substantially improved by the modification of hydroxypropylation and acetylation.By selecting experiments, the optimum formula was as follow: waxy rice flour 100%, hydroxypropylated waxy rice starch 100%, acetylated waxy rice starch 0.5% in total, water 110% in total, sugar 20% in total, water-soluble monoglycerides 1% in total. The samples with addition of hydroxypropylated waxy rice starch had much better quality of anti-retrogradation than the product after stored at 4℃or -18℃for 30 days, respectively.
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