The objective of this study is to prepare zein/starch sodium octenyl succinate composite nanoparticles (ZSPs) via anti-solvent precipitation technology and characterize their colloidal properties. The effects of polar solvents, ultrasonic treatment time, and concentrations of starch sodium octenyl succinate were investigated. We measured the particle size distribution, hydrophobicity, and apparent structures of the composite nanoparticles. Ultrasonic treatment time (0-25 min) was found to play an important role in composite nanoparticle formation. The ZSP nanoparticles were with an average particle size in the range of 70 to 110 nm. When the ultrasonic treatment time exceeds 25 min, ZSPs became macroscopic particles. The fluorescence spectrum and three-phase contact angle indicated that ZSPs presented hydrophilicity with largest threephase contact angle, which was 65.1 • . Fourier transform infrared spectroscopy and scanning electron microscopy revealed that hydrophilic SSOS absorbed on the surface of zein nanoparticles via Van der Waals to improve their water solubility. The changes in solvent polarity and zein self-assembly are considered to be the main driving force for composite nanoparticles conformational transitions from α-helix to β-sheet. Differential scanning calorimetry analysis indicated that ethanol combined ultrasonic treatment (10 min) was beneficial to enhance the thermal stability of composite nanoparticles, causing the highest T g of 153.6 • C. This work aims to provide a practical reference for formulating delivery systems using bioactive compounds containing zein as a carrier biopolymer.Practical Application: This work aims to provide a practical reference for formulating encapsulants for food and other bioactive compounds containing zein as a carrier biopolymer. Zein/starch sodium octenyl succinate composite nanoparticles formulated in this study provide novel stabilizers for emulsification systems or carriers of bioactive substances that can enhance the nutritional value, taste, or shelf life of foods.

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