2.2.1. Preparation Individual Solution

Zein stock solution, which was zein dissolved in 70% (*v*/*v*) ethanol at 25 mg/mL followed by continuous shaking for 1 h at 25 ◦C prior to ultrasound treatment.

FSG stock solution was completely dissolved in water at 5 mg/mL by magnetic stirring at 95 ◦C for 1 h, the pH was adjusted to 4.0 with 0.1 M HCl or NaOH solutions and measured by a pH meter.

#### 2.2.2. Preparation of Zein Nanoparticles (ZNP)

Zein nanoparticles (ZNP) were prepared by anti-solvent precipitation method according to Dai, L. [26]. Briefly, 20 mL of zein stock solution was added dropwise into 60 mL deionized water in an ultrasonic water bath (KH-300DE, Kunshan Hechuang Ultrasonic Instrument Co., Ltd., Kunshan, Jiangsu, China). After magnetic stirring for 30 min, the remained ethanol in the particle dispersions was removed by rotary evaporation (IKA RV 8, IKA Works Guangzhou, China). The final concentration of ZNP was 10 mg/mL. Finally, the pH value of ZNP dispersions was adjusted to 4.0 with 0.1 M HCl or NaOH solutions using a pH meter and stored at 4 ◦C until use. The nanoparticles are made from natural or ultrasonic zein separately.
