Abstract: Carboxymethyl cassava starch was synthesized from cassava starch with monochloroacetate (MCA) as an etherifying agent and sodium hydroxide (NaOH) as a catalyst by mechanical activation-assisted solid-state reaction. One-factor-at-a-time and orthogonal array design methods were used to optimize the preparation conditions for higher degree of substitution (DS). The structure of carboxymethyl cassava starch was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope (SEM) and its physicochemical properties were systematically investigated. The optimal process parameters that provided maximum DS of 0.540 1 were obtained as follows: molar ratio of starch to sodium chloroacetate 1:1, reaction temperature 50 ℃, reaction time 1.5 h, sodium hydroxide concentration 18.8%, stirring speed 380 r/min, and volume of?ball milling medium 500 mL. The etherification reaction of cassava starch was confirmed by FTIR, XRD and SEM. Results of the physicochemical properties showed that the solubility of carboxymethyl cassava starch and the viscosity of starch paste and were significantly increased; water-absorbing capacity, water-retaining capacity, freeze-thaw stability, and acid, alkali and enzyme resistance were also improved compared with the native starch.

Key words: mechanical activation-assisted solid-state reaction, carboxymethyl starch, degree of substitution, characterization, physicochemical properties