Low-pressure cold plasma-induced structural reinforcement of pea protein-alginate complexes to improve encapsulation and stability of cinnamon essential oil-loaded microcapsules

This study examined the application of low-pressure cold plasma (CP) as a non-thermal approach to modify pea protein isolate (PPI) prior to its use in protein-polysaccharide matrices for encapsulation of cinnamon essential oil (Cin). PPI was first treated with CP and subsequently combined with AG at an optimized ratio (3:1, w/w) to form the wall material, followed by Cin loading and freeze-drying. Moderate CP exposure (60 W, 4 min) produced a slight reduction in particle size and noticeable changes in surface charge and conductivity, indicating altered colloidal behavior without compromising the primary protein structure, as confirmed by SDS-PAGE. FTIR spectroscopy and amide I deconvolution further revealed CP-induced secondary structure rearrangement and modified interaction between PPI and AG. Isothermal titration calorimetry (ITC) provided direct thermodynamic evidence of these interactions, showing enhanced binding affinity and more favorable complexation between PPI and AG after CP treatment. The resulting complexes were used to encapsulate Cin, and the freeze-dried powders were characterized for moisture content, water activity, hygroscopicity, solubility, and encapsulation efficiency. Although most physicochemical parameters showed only moderate variations, CP-treated complexes exhibited improved stability under different ionic strengths, pH conditions, and prolonged storage. Enhanced resistance to color change, thermal stability, oxidative degradation, and light exposure were also observed compared to untreated systems. Antimicrobial activity against Escherichia coli and Listeria monocytogenes was retained after encapsulation, while CP treatment did not significantly alter the immediate antibacterial effect. Furthermore, in vitro gastrointestinal digestion using the INFOGEST model indicated that AG incorporation and CP treatment enhanced structural integrity under gastric conditions. Overall, low-pressure CP treatment induced selective and controlled structural modifications in PPI that influenced its interaction with AG and primarily improved the environmental stability of Cin-loaded microcapsules. These findings highlight the potential of this approach for plant-based delivery systems in food applications.