Caffeic acid-grafted high-amylose maize starch for self-stabilizing emulsion gels: efficient encapsulation and protection of pterostilbene

Caffeic acid was grafted onto starch (Cf-HAMS) via C-6 esterification. • Caffeic acid grafting simultaneously enhanced amphiphilicity and bioactivity. • Cf-HAMS solely stabilized emulsion gels via reinforced interfacial films and networks. • Emulsion gels enhanced pterostilbene stability and in vitro bioaccessibility. Caffeic acid-grafted high-amylose maize starch (Cf-HAMS) with grafting degrees of 4%, 8%, and 12% was synthesized via esterification to address the limitations of native HAMS in emulsion-gel stabilization. Nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) confirmed covalent grafting at the C-6 hydroxyl groups. Due to the introduction of caffeic acid's phenolic hydroxyls and aromatic rings, Cf-HAMS exhibited markedly enhanced hydrophobicity (contact angle from 26.8° to 65.1°) together with strong antioxidant and antibacterial activities. Consequently, Cf-HAMS alone, without any added surfactants, stabilized emulsion gels with smaller droplets, reinforced interfacial films, and enhanced viscoelasticity. When applied as carriers for pterostilbene, Cf-HAMS achieved approximately 90% encapsulation efficiency, improved UV and thermal protection, suppressed lipid oxidation, and increased bioaccessibility by a factor of 2.5 compared with native HAMS. Overall, these findings demonstrate that phenolic-acid grafting effectively integrates interfacial stabilization with chemical protection for hydrophobic bioactives. Download: Download high-res image (224KB) Download: Download full-size image