Synthesis of octenylsuccinic-anhydride-modified cassava starch in supercritical carbon dioxide

The aim of this work was to synthesize octenylsuccinic-anhydride-modified starch (OSAS) via esterification of cassava starch and octenylsuccinic anhydride (OSA) in supercritical carbon dioxide (ScCO2). Using ScCO2 as the medium and hexamethylene as the co-solvent, a reaction efficiency of 84.47% was obtained using 4 wt% OSA. The ester carbonyl groups were successfully introduced into the starch molecule, which was confirmed via FTIR and NMR spectroscopy. In the present study, ScCO2 was an excellent processing aid for the synthesis of OSAS because it could dissolve OSA, allowing the OSA to diffuse into the starch granules. This resulted in esterification occurring on the starch granule surface and in the interior of the starch granule, which led to an even distribution of the substituted groups in the starch granule. As a result, the esterification altered the morphology of the starch granules, and the relative crystallinity of the starch decreased from 36.66 to 30.99% compared to that of cassava starch. Additionally, the OSAS prepared in ScCO2 exhibited a lower gelatinization temperature and a higher peak paste viscosity than the products prepared using a dry method, which indicated that the OSAS prepared in ScCO2 can be used as an effective thickener.