Insights into conformational and hydrogel performance of silk fibroin treated by cold plasma

Silk fibroin (SF), a biopolymer derived from Bombyx mori, offers excellent biocompatibility, biodegradability and mechanical tunability, making it ideal for applications such as food structure formation, controlled release and active ingredient encapsulation. However, native SF hydrogels exhibit slow gelation under physiological conditions, limiting practical use. Cold plasma (CP) treatment effectively enhanced the surface hydrophobicity and charge density of SF by inducing partial protein unfolding and promoting aggregation through oxidative cross-linking. This led to a conformational shift from α-helix to β-sheet, strengthening intermolecular interactions. Compared with SF, CSF-8 (treated with CP for 8 min) formed a more compact and stronger three-dimensional structure. This enhancement significantly improved its water retention capacity and gel strength. The water retention capacity increased by 25.3%. The compressive stress at 50% strain rose from 15.2 kPa to 39.2 kPa. The gel hardness increased from 12.5 N to 34 N. The gelation time of CSF-8 was reduced by 81.2%, indicating that prolonged exposure promoted faster hydrogel formation. This study highlights CP as a green, tailoring SF structure and gelation via non-chemical strategies provides promising avenues for hydrogel design in functional foods, including structure building, controlled release and active ingredient encapsulation.