Characterization of acid hydrolysis of granular potato starch under induced electric field

Abstract

Compared to traditional heating methods by static immersion or stirring, induced electric field (IEF) treatment can significantly increase hydrolysis rate of potato starch. The aim of this study was to examine the characterization of acid hydrolysis of granular potato starch under IEF. Potato starch was hydrolyzed using 0.15 mol/L HCl combined with IEF (IEF-HCl) at an excitation voltage of 75 V from 4 h to 120 h. The changes in granular, crystal, and molecular structure of starch granules during IEF-HCl hydrolysis were investigated. Scanning electron microscope analysis showed the outer surface of potato starch was firstly attacked by free ions and then the inner structures was completely disrupted and broken into pieces. X-ray diffraction studies indicated that the crystallinity decreased from 38.92% to 34.9% after 4-h hydrolysis, and then gradually increased to 41.88% as hydrolysis time increased to 96 h, but decreased thereafter. The weight-average molecular weight dramatically decreased from 104.7 × 106 Da to 9.291 × 106 Da in the first 24 h and then decreased gradually. These results suggested that there were three steps in the catalytic process of IEF-HCl hydrolysis. Initially, hydrogen ions destroyed the external crystalline shell of granules. Next, hydrogen ions attacked the loose amorphous region and dense crystalline part within starch granules simultaneously. Finally, the remaining crystalline region was hydrolyzed slowly.