Preparation of Acetylated Citric Acid Esterified and Cross-linked Mechanically Activated Starch and the Analysis of Their Properties
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Abstract:
Acetylated citric acid esterified and cross-linked starch was prepared by the solvent method, with mechanically activated cassava starch as material, acetic anhydride as esterification agent, and citric acid as cross-linking agent. The effects of mechanical activation time, amount of mixed acids, reaction temperature, reaction time, and mass ratio of citric acid to acetic anhydride on the sedimentation volume of acetylated citric acid esterified and cross-linked starch were investigated. The structure and properties of the as-prepared esterified and cross-linked starch were characterized and determined. The results showed that the optimum technological conditions were as follows: mechanical activation time of 40 min, addition amount of mixed acid of 10% (accounting for dry weight of starch), reaction temperature of 45 ℃, reaction time of 1 h, and the mass ratio of citric acid to acetic anhydride of 1:35, the sedimentation of product was 1.52 ml. FT-IR showed that the starch was successfully esterified and cross-linked. X-ray diffraction (XRD) showed that the esterification and cross-linking reactions occurred in the amorphous region of starch. The results showed that the order of water extraction rate and paste transparency is as follows: mechanical activated starch > raw starch > esterified and cross-linked mechanically activated starch > esterified and cross-linked starch, which indicates a better freeze-thaw stability and a lower paste transparency of esterified and cross-linked starch compared to those of raw starch. In addition, the order of acid-resistance properties is as follows: esterified and cross-linked mechanically activated starch > mechanically activated starch > esterified and cross-linked starch > original starch, indicating that mechanical activation can improve the acid-resistance property of starch. Furthermore, the viscosity thermal stability of esterified and cross-linked starch is better than that of raw starch. In general, the mechanical activated esterification cross-linked starch displays a better freeze-thaw stability, acid-resistance property and viscosity thermal stability.
