Role of surfactant in the formation of zein/Tween-20 nanoparticles studied by fluorescence and circular dichroism

The formation of zein/Tween-20 nanoparticles through the antisolvent precipitation method at various Tween-20 concentrations (CTween-20) has been investigated using dynamic light scattering, surface tension, fluorescence, and circular dichroism. When CTween-20 increases from 0 to 0.2 g/L, the particle sizes of zein/Tween-20 nanoparticles significantly decrease from 140 to 95 nm, followed by nearly constant values of 90–92 nm at CTween-20 = 0.2–4 g/L. Compared to Tween-20, zein/Tween-20 nanoparticles give smaller values of surface tension at CTween-20 = 0–2.8 g/L, and almost the same values at CTween-20 higher than 2.8 g/L. The values of fluorescence maximum intensity and α-helix content of zein molecules in zein/Tween-20 nanoparticles show pronouncedly different changes at CTween-20 = 0–0.2, 0.2–2.8, and 2.8–4 g/L. The formation of zein/Tween-20 nanoparticles is proposed to be induced by the aggregation of zein/Tween-20 complexes mainly driven by the hydrophobic force. Zein/Tween-20 complexes exhibit different structural properties at low, intermediate, and high Tween-20 concentrations.