Comparison Study of Structural, Physiochemical, and Functional Properties and In Vitro Digestibility of Citric Acid Starch Esters With Distinct Amylose Content

To better understand the effect of citric acid esterification on starch with distinct amylose content and their associated properties, citric acid starch esters were prepared by using three corn starches, including waxy corn starch (WCS, AM: ∼5%), normal corn starch (NCS, AM: ∼24%), and high amylose corn starch (HACS, AM: ∼73%). The impact of citric acid esterification on the morphological, structural, and physicochemical properties and in vitro digestibility was investigated. The degree of substitution (DS) for waxy corn starch ester (WCSE), normal corn starch ester (NCSE), and high amylose corn starch ester (HACSE) was 0.1631, 0.1199, and 0.1552, respectively. The incorporation of ester groups to native starch molecular chains was further confirmed by FTIR and ¹H NMR. Starch esters exhibited more pronounced disruption of crystalline structure, and the relative crystallinity showed the order of HACSE > WCSE > NCSE. Esterification resulted in the depolymerization of natural starch chains, showing the decreased degree of polymerization. According to the CLD results, WCSE exhibited the lowest degree of polymerization. The solubility, swelling capacity, apparent viscosity, and transparency of starch esters were decreased significantly compared to native starches, whereas the thermal stability was improved. In vitro digestion analysis revealed esterification of cornstarch elevated the content of resistant starch (RS). Compared to native starch, starch esters exhibited increased RS content by 47.89% (WCSE), 24.53% (NCSE), and 14.98% (HACSE), respectively. This study provided a reference for citric acid starch esters with varied amylose content and their potential as functional ingredients in the food industry.