Structural and physicochemical properties of chemically modified Chinese water chestnut [Eleocharis dulcis (Burm. f.) Trin. ex Hensch] starches

Chinese water chestnut [Eleocharis dulcis (Burm.f.) Trin. ex Hensch] is a starch-rich aquatic plant widely consumed throughout the oriental countries. In this study, different chemically modified Chinese water chestnut starches including acetylated starch (AS), succinylated starch (SS) and carboxymethylated starch (CMS) were prepared. The structural and physicochemical properties of native starch and chemically modified Chinese water chestnut starches were compared for the first time. The degrees of substitution for AS, SS and CMS were 0.087, 0.575 and 0.972, respectively. Results of powder X-ray diffractometry, small-angle X-ray scattering and scanning electron microscopy indicated the crystalline regions and morphology of native starch were destroyed by chemical modification. Notably, carboxymethylation completely destroyed the original morphology of native starch and thus CMS exhibited an amorphous state. Besides, AS and SS showed significantly lower gelatinization properties than native starch. The thermal stability decreased in the order of CMS > AS > native starch > SS, whereas viscoelastic properties decreased in the order of SS > CMS > native starch > AS pastes. Notably, CMS exhibited the highest swelling power, solubility, paste clarity and resistant starch content, implying CMS might have wide applications in food industry.