Analysis of the effect mechanism of wet grinding on the film properties of pea protein isolate based on its structure changes

Pea protein isolate (PPI) is a spherical structure with low intermolecular crosslinking, resulting in low tensile strength and hydrophobicity of the PPI film. In this study, wet grinding (WG) treated pea protein isolate was used, and protein films were prepared from the wet-ground pea protein isolate (WG-PPI). The structural changes of WG-PPI were investigated, and the effect mechanism of wet grinding on the properties of PPI films was discussed by the analysis of the relationship between the structural changes of PPI and the properties of PPI films. The results showed that after wet grinding for 10 min, α-helix, and β-turn increased to 12.07% and 31.37% respectively, while β-sheet and random coil decreased to 31.80% and 24.76%. The particle size decreased from 1365.87 nm to 1068.03 nm, and the free sulfhydryl group increased from 3.91 μmol/g to 6.04 μmol/g. Meanwhile, tryptophan residues were exposed. These changes enhanced the protein-protein and protein-glycerol interactions. Therefore, after wet grinding for 10 min, the film opacity decreased to 1.15 A/mm, the water vapor permeability decreased to 3.45 × 10−9·g·m·m−2·s−1·Pa, the contact angle increased from 56.48° to 72.37°, the tensile strength increased from 1.20 MPa to 2.72 MPa, the elongation at break increased from 74.9% to 166.8%, and the surface of the film was uniform and dense. In conclusion, it could be seen that moderate WG could significantly improve the properties of PPI films.