Abstract:Tapioca starches were used as the raw material and propionic anhydride was used as esterification agent to prepare propionylated starches with degrees of substitution（DS）of 0.81，1.53 and 2.67.The physicochemical properties of propionylated starches were characterized by Fourier transform infrared spectroscopy（FTIR），nuclear magnetic resonance hydrogen spectrum（1HNMR），scanning electron microscopy（SEM），X-ray diffraction（XRD）techniques，etc.The presence of propionyl group was confirmed by the presence of ester carbonyl group（C=O）at 1 740 cm-1in the FTIR profile of propionylated tapioca starches，and the presence of new proton peaks at 1.0 ppm and 2.2 ppm in the1HNMR profile further verified the occurrence of propionylation.After propionylation，the propionyl groups gradually replaced the hydroxyl groups on the starch anhydrous glucose units，resulting in the reduction of the inter-or intra-molecular hydrogen bond interaction，which improved the thermal stability and hydrophobicity of starch molecules.The results were consistent with thermogravimetric analysis（TGA）and contact angle determination.The results of XRD showed that with the increase of DS，the A-type crystal structure of tapioca starches was gradually destroyed，and the corresponding relative crystallinity decreased from 47.34%to 22.28%.The results of SEM showed that the destruction degree of propionylated starch particles increased with the increase of DS.In addition，the in vitro digestion test showed that with the increase of DS，the content of resistant starch in tapioca starches increased from 13.25%to 82.31%after modification.