Dual modification of sweet potato starch: Effects of sequence based on ultrasound-assisted nanoprecipitation and OSA esterification for superior functional properties

This study innovatively combined ultrasound-assisted nanoprecipitation with octenyl succinic anhydride (OSA) esterification for dual modification of sweet potato starch (SPS), systematically investigating the impact of modification sequence (nanoprecipitation-first vs. OSA-first) on functional properties. The results showed that OSA-modified nano precipitated SPS (OSA nano SPS) achieved a 10.8 % higher degree of substitution (DS: 0.0184) than nano precipitated OSA-modified SPS (nano OSA SPS, DS: 0.0166), attributed to enhanced OSA accessibility via prior nano structuring. Ultrasonication reduced starch particle size to 77.01 nm and increased amylose content (244.23 mg/g), resulting the increased solubility and the decreased swelling capacity. OSA esterification of SPS was confirmed by FT-IR, with characteristic peaks at 1729 cm^-1 (C=O) and 1564 cm^-1 (-COONa), improved hydrophobicity (90° contact angle) and formed V-type crystalline structures confirmed by XRD. SEM and TEM analyses conclusively demonstrated that OSA nano SPS exhibited structurally integrated nanoparticles with enhanced surface uniformity and controlled size distribution, while nano OSA SPS displayed irregular aggregates compromising structural integrity. OSA nano SPS exhibited superior Pickering emulsion stability, maintaining over 80 % emulsification index after 120 h, with rheological properties surpassing single-modified counterparts. The work first elucidates the sequence-dependent mechanism of dual modifications, demonstrating that nanoprecipitation before esterification optimizes reaction efficiency and emulsion performance. These findings provide a paradigm for designing starch-based delivery systems through controllable multi-step modification strategies.