Internal structure of high degree substitution acetylated potato starch by chemical surface gelatinization

To understand the contribution of granule inner portion to the pasting property of acetylated potato starch under the electric field and ultrasonic treatment, these starches were subjected to chemical surface gelatinization by 4.0 mol/L CaCl₂ to obtain remaining granules with pasting time 0, 6, 12, 18, 24, 30 min, respectively. The structure of remaining granule was studied by the fitted distribution curve. Their morphological change, crystal structure and thermal property were investigated with scanning electron microscopy (SEM), X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). The degree of substitution was obviously improved (DS was 0.37). The distribution curve of acetyl groups and amylose content showed that acetyl groups, both amylose and amylopectin populations were unevenly distributed. A large extent of acetylation took place in the outer lamellae. The SEM presented that the remaining potato starch granules had a rough surface with a lamella structure. The XRD and DSC showed that the acetylation was confirmed to mainly occur the amorphous region and only take place in the outer lamellae of crystalline regions of starch granule. The distribution of amorphous and crystalline regions was uneven. Chemical gelatinization was a process of stepwise removal of the outer layer.