Hydrophobic Modification of Food-Grade Starch Nanoparticles by Acetylation and Its Digestion Characteristics

Cassava starch nanoparticles with an average size of (273.8 ± 26.41) nm were prepared by ultrasonic crushing followed by ethanol sedimentation and were esterified with acetic anhydride to prepare hydrophobic nanoparticles. Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy showed that the degree of substitution (DS) of the esterified products was as high as 0.53 without adding any catalysts during esterification. X-ray diffraction (XRD) analysis showed that the crystal structure of starch nanoparticles did not change significantly after modification, and both the original and modified nanoparticles were amorphous. Scanning electron microscopy (SEM) showed that the morphology of the nanoparticles did not change significantly after modification. The three-phase contact angle increased with increasing DS, reaching a maximum of (109 ± 3.56)°, and the higher the DS, the longer the contact angle was maintained. The modified product was easier to disperse in the oil phase, leading to the formation of microemulsions. Surface modification changed the hydrophilic/hydrophobic properties of starch nanoparticles, and improved its potential for emulsification at the oil-water interface. In contrast to the unmodified sample, the modified sample showed similar enzymatic digestion curves and no fundamental change in eating quality, but lower enzymatic digestibility at the same time points, suggesting stronger resistance of the modified product with higher DS to enzymatic hydrolysis.