Mechanism of zein self-assembly fibrillation induced via plasma-assisted acid-heat treatment: Influence of the fibrillation degree

Protein fibrillation displays great potentials in protein modification with favorable attributes in food industry. Due to the alcohol solublility and limited β-sheet content, however, the fibrillation degree of zein was not ideal simply through traditional acid-heat treatment. In this study, cold plasma technology was employed to assist the acid-heat treatment to improve zein's fibrillation degree. The physicochemical properties and molecular structure changes of zein fibrils with different fibrillation degrees (ThT fluorescence intensities from 1358 to 2272, named as PZF1–5) were investigated. Results indicated that plasma-assisted fibrillation resulted in zein fibrils with more surface charge and smaller particle sizes than natural zein. After fibrillation, the average particle size of zein decreased from 879.57 ± 155.52 nm (natural zein) to the minimum of 123.80 ± 10.26 nm (PZF3). Plasma treatment significantly increased the content of β-sheet and disulfide bonds (p < 0.05) and transformed zein from a globular morphology to bead-like fibrils. Compared with the zein fibrils without plasma pretreatment, plasma discharge could generate more disulfide bonds within zein as the content remarkably increased to 9.52 ± 0.07 μmol/g (PZF5). Based on the above, the driving force of plasma-assisted self-assembly fibrillation mainly involved electrostatic interactions, hydrogen bonds and disulfide bonds. Notably, improved emulsifying capacity was observed for the plasma-treated zein fibrils, with the creaming index positively correlated to the fibrillation degree. These findings provided valuable insights into zein fibrillation and demonstrated the potential of cold plasma as a supportive method for protein fibrillation.