Effects of rice starch esterified with citric acid and malic acid: Functional properties and structural...

Rice starch faces limitations in healthy food applications due to its rapid digestibility, which leads to high glycemic responses. To regulate its digestion properties, this study employed citric acid (CA) and malic acid (MA) for esterification modification of rice starch, systematically comparing their differences in degree of substitution (DS), structure, and functional properties. Results demonstrated that, owing to its structural advantage of three carboxyl groups, CA exhibited significantly higher modification efficiency than MA. Under 40 % acid concentration, the DS of CA-modified starch (0.650) was more than twice that of the MA-modified product (0.320). Structural analyses revealed that esterification disrupted the crystalline regions and hydrogen bonding network of starch, resulting in reduced gelatinization enthalpy, while forming a more homogeneous amorphous structure. Most importantly, in vitro digestion experiments confirmed that modification significantly increased the resistant starch content, particularly in CA-modified starch (CRS), which achieved an RS content as high as 62.0 % and an estimated glycemic index (GI) of 54.8. This study elucidates an effective method for regulating the digestibility of rice starch through organic acid esterification, providing a theoretical foundation for its high-value application in the development of low-GI healthy staple foods.