Effect of solvent polarity on the formation of flexible zein nanoparticles and their environmental adaptability

Zein possesses strong self-assembly ability due to its amphiphilicity. To investigate the effect of solvent polarity on both the flexibility of zein and the formation of flexible zein nanoparticles, various ethanol aqueous solutions were chosen. Alkaline modification was applied to improve the flexibility of the zein and a liquid-liquid method was used to produce zein nanoparticles. Solvent polarity plays a positive role in improving the flexibility of zein. Furthermore, native and flexible zein nanoparticles were formed from native zein and flexible zein, respectively. However, nanoparticles could not form from highly flexible zein due to their strong adaptability to changes in solvent. Compared with the emulsifying activity index (EAI) and emulsifying stability index (ESI) of native zein nanoparticles, a higher EAI and ESI of flexible zein nanoparticles were acquired. These results may be attributed to the strong adaptability of flexible zein to the medium changing through changing their secondary structure. Furthermore, the adaptability of flexible zein nanoparticles significantly depended on the initial polarity of the solvent. The deamidation reaction of zein was responsible for the change in zein flexibility. These findings thus provide clear evidence of the relationship between the solvent polarity and structural flexibility of modified zein.