Synthesis and characterization of citric acid esterified canna starch (RS4) by semi-dry method using vacuum-microwave-infrared assistance.

In this study, citric acid (CA) esterified canna starch was firstly synthesized with the aid of vacuum, microwave and infrared radiation treatment. The changes in structural, physicochemical properties and in vitro digestibility of the modified starch were then investigated. The maximum degree of substitution (DS) reached 0.273 and the maximum thermo-stable resistant starch (RS) content reached 86.5 %. FT-IR confirmed the esterification reaction had successfully occurred, XRD and DSC results revealed that the crystalline and endothermic peaks of the samples disappeared after CA-treated, and TGA showed that the thermal degradation temperatures were above 280 °C. SEM showed the destroyed surface of the starch granules. All modified samples were lighter and generally whiter than native canna starch in color. These results suggest that the aid of vacuum treatment, microwave and infrared radiations for CA esterified of canna starch is an effective method for preparing high content of thermally stable RS4.