Tailoring soy protein techno-functional properties through cold plasma treatments: air vs. CO₂ approaches

• Plasma gas composition influenced SPI structural and techno-functional properties. • Air plasma increased random coil, while CO₂ promoted β-sheet formation. • Air-based plasmas enhanced solubility and foaming, whereas CO₂ improved WHC. • All plasma treatments strengthened SPI gels and effectively reduced syneresis. This study investigated the effects of cold plasma treatments with air (80% N 2 , 20% O 2 ), pure CO₂, and a 1:1 air–CO₂ mixture on the techno-functional properties of soy protein isolate. Treatments were applied to protein dispersions (16% w/v in distilled water) for 30 min at a gas flow rate of 2 SLPM and a voltage of 160 V. FTIR spectroscopy was used to assess plasma-induced alterations in the secondary structure of SPI, and key techno-functional properties were studied, including solubility, foaming, water- and oil-holding capacities and emulsifying capacity. Gel strength, syneresis and rheological behaviour were also evaluated. Air plasma treatments increased the random coil structure and improved solubility and foaming properties. In addition, air plasma treatments created a more oxidative environment due to reactive species, evidenced by increased values of oxidation–reduction potential. On the other hand, CO₂ plasmas favoured β-sheet enrichment and increased water-holding capacity. All plasma treatments yielded gels with higher strength, lower syneresis and increased resistance to deformation (higher G′, G″ and complex viscosity). Overall, the results highlight that gas composition is a key factor in modulating plasma-induced techno-functional modifications of soy protein.