Morphological properties of acid-modified tapioca starch

Highly crystalline tapioca starch was prepared by partial hydrolysis of tapioca starch in hydrochloric acid at room temperature for various lengths of time. The crystallinity of the starch increased while its amylose content decreased with increasing reaction time. Scanning electron micrographs of these natural and highly crystalline starches were taken in order to study the morphological changes and mode of acid attack during hydrolysis. Exocorrosion all over the surface was observed after 96 h of hydrolysis. Further hydrolysis caused the outer layer of the starch grain surface to erode away. After complete erosion was accomplished, an inner layer or underlayer was revealed with a smooth surface similar to that of the native starch grain surface. Endocorrosion was not observed at any time in this study.