Gelatinization and Retrogradation of Hydroxypropylated Cornstarch

Gelatinization and retrogradation of a high amylose cornstarch modified by hydroxypropylation were studied by DSC. It was found that the gelatinization temperature of the starch was decreased and a narrow gelatinization range was measured by DSC after hydroxypropylation. The decreasing of the gelatinization temperature is explained by disrupting inter- and intra-molecular hydrogen bonds, while the narrowing of the gelatinization endotherm is explained by destroying the amylose-lipid complex. Morphologies of the starch granules with and without iodine treatment were studied under microscopy with normal and polarized lights. Brightness and birefringence decreased with increasing molar substitution since crystal structure in starch granular was partly destroyed. Weaker retrogradation was observed for the hydroxpropylated starch, ascribed not only to steric effects imposed by the bulky hydroxypropyl groups in amylopectin, but also to the removing of amylose-lipid complexes during alkaline treatment.