Effect of fibrillation on the film-forming properties of soy protein isolate: Relationship between protein structural changes and the film-forming properties

Protein fibrillation has great potential for enhancing the emulsification, foaming, and gelling properties of proteins. However, its effects on protein film-forming properties are less well understood. In this study, soy protein isolate (SPI) was subjected to fibrillation at pH 2.0 and 85 °C to prepare films plasticized with glycerol (2 %). Mature fibrils formed at 12 h, as confirmed by thioflavin T fluorescence assay, circular dichroism spectroscopy, and atomic force microscopy. Moreover, the structural changes of the fibrillar SPI were related to the resulting film characteristics. Rheological analysis confirmed that a dense gel network was formed during fibrillation. In addition, particle size increased, while the free sulfhydryl content and surface hydrophobicity decreased. Fourier transform infrared spectroscopy revealed strong hydrogen-bonded β-sheets were dominant in the fibrillar SPI film. The dense network and exposed amino acids in the fibrillar SPI film resulted in high tensile strength (4.91 MPa) and good ultraviolet-blocking properties.