Tailoring molecular, structural, and interfacial properties of soy protein isolate using in-package cold plasma treatment for stabilizing Pickering emulsions

Abstract

In-package cold plasma (ICP) is a widely used non-thermal method for microbial inactivation, but its potential for modifying food macromolecules remains largely unexplored. This study systematically evaluates the impact of different ICP treatment durations (1, 5, 10, and 20 min) on the structural, functional, and interfacial characteristics of soy protein isolate (SPI) to enhance its emulsifying performance. Among the treatments evaluated, a 5 min exposure produced the most desirable changes. This treatment induced partial unfolding of SPI through peptide bond cleavage. As a result, the surface hydrophobicity of 5 min ICP treated SPI (2406.15 ± 47.42) increased significantly compared to untreated SPI (1638.90 ± 45.04). The 5 min ICP treatment also induced significant structural alterations, including an increased random coil content and reduced α-helix and β-sheet structures. Additionally, it significantly reduced the particle size (221.76 ± 1.88 nm) compared to native SPI (246.16 ± 2.66 nm) due to structural disruption. Moreover, ICP induced oxidation of amino acid residues increased the zeta potential (−36.82 ± 0.64 mV) compared to native SPI (−30.66 ± 0.53 mV). Collectively, these modifications resulted in smaller emulsion droplet size (2.79 ± 0.78 μm), lower creaming indices, and improved viscoelastic properties. However, shorter treatment (1 min) had negligible effects, while prolonged exposure (20 min) caused excessive oxidation and protein aggregation, compromising emulsion stability. These findings indicate that intermediate-duration ICP treatment improves the structural and functional properties of SPI, making it suitable for stabilizing Pickering emulsions in food and nutraceutical applications.