The microstructure of starch consists of macromolecular cyclic structures composed of glucosyl units. Starch molecules possess a large number of hydroxyl groups, enabling them to react with various chemical reagents to produce a wide array of modified starches. Typically, chemical modification methods for starch include acid hydrolysis, oxidation, etherification, esterification, and cross-linking. Chemical methods represent the most widely applied approach in starch modification.
Acid hydrolysis is extensively utilized within the starch industry. Jianmin Man et al. investigated the acid hydrolysis of high-amylose transgenic rice starch under conditions of 2.2 mol/L HCl. During the acid hydrolysis process, the gelatinization temperature decreased during the initial phase, while the hydrolysis temperature increased during both the peak hydrolysis phase and the final stage. The endothermic value initially increased and subsequently decreased as acid hydrolysis progressed, while both the swelling power and solubility of the high-amylose transgenic rice starch increased. Starch hydroxypropylation is a specific form of starch etherification; hydroxypropylated starch can mitigate starch degradation and alter characteristics such as gelatinization temperature and paste viscosity.
Olayide S. Lawal et al. found that following hydroxypropyl modification, finger millet starch exhibited enhanced free swelling capacity and molar substitution degree, while its turbidity, retrogradation percentage, and degradation rate were reduced. Cross-linking and esterification are frequently employed to modify native starch, particularly for the production of materials with low water sensitivity. Esterification imparts hydrophobicity to starch products through the substitution of hydroxyl groups. The objective of cross-linking treatment is to introduce additional intra- and intermolecular linkages at random sites within the starch granules; furthermore, by increasing the density of cross-linkages within the starch structure, this treatment also serves to limit water absorption.
