Microwave assisted synthesis and characterization of acetate derivative cassava starch.

摘要

Use of microwave heating for the acetylation of cassava starch was investigated, together with the physicochemical properties of the starch acetate obtained. Acetylation was carried out by mixing native cassava starch with chloroacetic acid and sodium hydroxide in a sealed container. The mixture was then sprayed with ethanol and heated using microwave power. The degree of substitution (DS), reaction efficiency (RE) and some physical properties of the acetylated starches were then analysed. It was found that microwave assisted acetylation of cassava starch using chloroacetic acid could be achieved in a very short time. The highest DS and RE obtained were 0.045 and 0.051%, respectively. Acetylation of cassava starch reduced gel hardness during storage. Acetylation also inhibited retrogradation of starch gels. Cassava starch acetylation changed starch molecular motion, resulting in a decrease in the glass transition temp. Amylopectin retrogradation was not significantly reduced, indicating that the extent of starch modification achieved in this study was too low to cause sufficient steric hindrance to prevent retrogradation. Modification was performed on native starch granules; it took place preferentially on the amylose fraction, not the amylopectin fraction, hence amylopectin retrogradation was mostly unaffected. It is concluded that microwave heating can be applied to the acetylation of cassava starch to obtain significant changes of the properties of the starch.