Effect of acid hydrolysis on the multi-scale structure change of starch with different amylose content

Abstract

This work demonstrates how the multi-scale structure of starch granules changes during acid hydrolysis. The degradation mechanism has also been discussed. Both the whole native Gelose 80 (G80) starch in its granule form and the enzyme debranched G80 starch degraded apparently until a stable size was reached. In contrast, no degradation of the debranched waxy starch was observed from size exclusion chromatography (SEC) results. This indicated that amylose and amylopectin were hydrolyzed through cleavage of α-(1 → 4) and α-(1 → 6) linkages, respectively. From X-ray diffraction (XRD), the relative crystallinity was increased with increased acid treatment days. Small-angle X-ray scattering (SAXS) results showed that the lamellar peak intensity and crystalline thickness (dc) from 1D correlation function for G80 were increased during acid hydrolysis. However, the lamellar structure of waxy starch disappeared quickly. Using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), two different acid hydrolysis patterns were observed at the starch granule level including the endo-corrosion pattern in waxy starch and the exo-corrosion pattern in G80. Those differences would lead to the quick degradation of the lamellar structure of waxy starch and contributed to the gradual crystallinity increase for G80 starch. Thermal degradation behavior from thermogravimetric analysis (TGA) results showed that the thermal decomposition temperature of acid-hydrolyzed starch was shifted to low temperature, which confirmed the molecular weight degradation during acid hydrolysis. This work enables a further understanding of acid hydrolysis mechanism, which is of value for the acid processing of starch-based foods.