Stearic acid-functionalized high amylose starch nanoparticles: Tailoring interfacial wettability and thermal stability via fatty acid localization.

High amylose starch nanoparticles (HSNPs) were functionalized with stearic acid (SA) to enhance their efficacy as Pickering emulsion stabilizers. Through ethanol pre-washing, removable and residual SA fractions were differentiated, revealing that removable SA primarily dictates surface hydrophobicity. Specifically, 8% SA loading increased the contact angle from 68° to 80°, indicating enhanced surface hydrophobicity and favoring particle adsorption at the oil-water interface. Emulsions stabilized by HSNP-SA composites exhibited superior stability, with unwashed 8% SA samples achieving a 100% emulsion index. Furthermore, SA incorporation significantly enhanced thermal resistance; while untreated HSNPs showed 15% oiling-off under thermal stress (100 °C for 20 min), the 8% SA variant reduced this to less than 6%. PCA confirmed that interfacial and thermal properties, rather than particle size, predominantly govern emulsion stability. These findings establish that SA localization critically modulates the structure-function relationship of starch nanoparticles, providing a clean-label strategy for developing thermally stable Pickering emulsifiers.