Abstract: Quercetin-carboxymethyl sweet potato starch ester was synthesized by covalent attachment of quercetin to carboxymethyl sweet potato starch. The influence of preparation conditions on the degree of substitution (DS) was investigated by the combined use of one-factor-at-a-time (OFAT) method and response surface methodology (RSM). The OFAT results indicated that the DS increased with increasing molar ratio of quercetin to anhydroglucose unit (AGU) of sweet potato starch (Nquercetin/AGU), while it increased then decreased with increasing molar ratio of activating agent to AGU (NEDC/AGU) and reaction pH. Furthermore, the RSM results revealed that both NEDC/AGU and reaction pH had a significant effect on the DS (P < 0.01), while Nquercetin/AGU as well as the quadratic and interactive terms showed no significant effect on the DS (P > 0.05). Finally, the optimal reaction conditions were obtained as follows: carboxymethyl sweet potato starch concentration 51 g/L, Nquercetin/AGU 2:1, NEDC/AGU 1.8:1 and initial pH 7.4. The maximum DS value of 0.114 9 was obtained under the optimized conditions. The covalent linkage of quercetin to carboxymethyl sweet potato starch was confirmed by detectable quercetin release from the product after hydrolysis.

Key words: modified starch, quercetin, carboxymethyl starch, quercetin-carboxymethyl sweet potato starch ester, esterification