Vacuum cold plasma-induced structural modifications of soy protein isolate: A denaturation pathway for enhanced electrospinning

The effects of “vacuum” cold plasma (VCP) treatment on the structure of soy protein isolate (SPI) have not yet been investigated. Thus, VCP durations of 5, 10, and 15 min at 60 and 80 W (6 samples in total) were selected to amend the SPI structure prior to electrospinning. VCP applies reduced pressure, refines the SPI structure, and enables deeper penetration of high-energy species. This structural rearrangement is essential for electrospinning, as native globular SPI must be converted to a random-coil conformation. The evaluated properties of VCP-treated SPI comprised protein solubility, sulfhydryl content, surface hydrophobicity, turbidity, rheology, secondary structure, and molecular dynamics simulations. The results indicated that at 60 W, a 10 min VCP was needed for optimal physicochemical properties and higher denaturation, whereas at 80 W, only a 5 min VCP was required. This suggests that a higher VCP power reduces the required treatment time, as it generates greater electron density and more active species in the plasma. VCP increased the viscosity of SPI samples. All treatments enhanced the α -helix to β -sheet ratio and disordered structures, except for VCP, for 15 min. The decrease in β -sheet structure after VCP may be due to the probable oxidation of amino acid residues. Molecular dynamics simulations validated the electric field-induced unfolding of 7S globulin, showing a shift from ordered secondary structures to random coils. Finally, VCP treatment of SPI: PVA electrospun nanofibers reduced the diameter from 384 nm to 341 nm and decreased porosity from 72.0% to 70.6%."