Changes of property and morphology of cationic corn starches

Cationic starches with the degree of substitution (DS) ranging from 0.0075 to 0.1215 were prepared from the reaction of native corn starch with cationizing agent (3-chloro-2-hydroxypropyl)trimethylammonium chloride (CHPTAC) under the molar ratios of CHPTAC/AGU (anhydroglucose unit) = 1 and 1.71 in aqueous suspension at 40 °C for different reaction times (2, 5 and 24 h). Pasting and thermal properties of the cationic starches were evaluated by using a rapid-visco-analyser and differential scanning calorimetry, respectively. Morphological changes of the cationic starches were investigated by using scanning electron microscopy, confocal laser scanning microscopy, polarized optical microscopy, bright field microscopy, and wide angle X-ray diffractometry. The changes in the pasting and thermal properties, correlated well with the increase of DS, together with the characterizations of granular morphology of the cationic starches, pointed out the gradual reduction of the structural integrity of cationic starches with the rising in DS up to 0.0431, while evident physicochemical and morphological changes took place when DS was raised to 0.1215.