Synthesis, characterization and properties of acetylated high-amylose corn starch

High-amylose corn starch (HACS) is very attractive due to its peculiar physico-chemical characteristics associated with its high amylose content. The aim of this work was to obtain acetylated high-amylose corn starch (AHACS) under optimum acetylation parameters, using HACS as a raw material, acetic anhydride as an acetylating agent and sodium hydroxide as a catalyst. The acetylation parameters were optimized by the orthogonal test. Acetylated high-amylose corn starch (AHACS) was characterized by infrared spectroscopy, DSC and TGA. Its freeze-thaw stability, swelling power, blue value and retrogradation were measured and compared with those of HACS and corn starch (CS). The best conditions for preparing AHACS were: reaction temperature of 40 °C, reaction time of 2 h and pH 8.5. The thermal stability of HACS was poor because of the high amylose content. The effect of acetylation on the crystalline region of HACS was not obvious. HACS was more easily acetylated by acetic anhydride than corn starch. Acetylation had a positive influence on the freeze-thaw stability and retrogradation of HACS, and significantly increased its swelling ability. However, acetylation did not change the blue value of HACS. Also, acetylation led to a reduction of the onset temperature, peak temperature and end temperature, but to an increase in the melting enthalpy. When the temperature was higher than 600 °C, the amylose starch was easily broken down, compared with the amylopectin starch. The acetylation was capable of obviously improving the thermal stability of HACS.