Freeze-drying of oxidized corn starch: electrochemical synthesis and characterization

Oxidized corn starch (OCS) was successfully synthesized by electrochemical oxidation in aqueous solution of sodium chloride, and freeze-drying technology was also used for the post-processing of the prepared OCS. The synthesized OCS solutions were analyzed by viscosity measurement and UV-vis spectroscopies. The OCS samples were characterized by the determination of amylose and amylopectin contents, carboxyl and carbonyl groups contents, FT-IR, XRD, SEM and C-13-NMR. The analyses revealed that the viscosity of OCS solutions decreased with increasing current. The determination and characterization results indicated that the amylopectin decreased gradually, while the carboxyl and carbonyl groups contents of OCS increased by electro-oxidation. The introduction of carboxyl and carbonyl groups promoted OCS hydration and swelling. After electro-oxidation, the crystallinity of the OCS decreased, and the surface formed a loose and porous structure. The electro-oxidation was able to selectively oxidize the hydroxyl groups of the C-2, C-3, and C-6 positions by adjusting the current.