Effect of atmospheric pressure cold plasma treatment on charge, structure, thermal properties and coacervation behavior of Pea protein isolate with Alginate

Abstract

This study explores the characteristics and interactions of pea protein isolate (PPI) and alginate (AG) in complex coacervation, focusing on the effects of cold plasma (CP) treatment applied to the protein-polysaccharide mixture before coacervation and the influence of varying pH levels. CP treatment was applied at different durations (5, 10, 15, and 20 min) and with plasma characteristics analyzed through optical emission spectroscopy (OES) and current-voltage measurements. Emission spectroscopy of the nonthermal multi-needle corona discharge revealed prominent OH (A-X) and N₂ (CB) emissions with a gas temperature of 330 ± 5 K and electron density of (2.6 ± 0.1) × 10²¹ m⁻³. Following CP treatment, the coacervates were characterized using Turbidity, Zeta potential, Particle size, Fourier Transform Infrared Spectroscopy (FTIR), Thermal Analysis (TGA and DSC), and Isothermal Titration Calorimetry (ITC). CP treatment resulted in a ≈ 33.4 % reduction in particle size and improved transparency, as indicated by reduced turbidity. Zeta potential analysis showed a 41.7 % increase in the negative charge for PPI-AG (2:1) at pH 4 after 20 min, enhancing the stability and coacervation efficiency. FTIR analysis indicated a 25.56 % reduction in β-sheets, with a 52.34 % increase in α-helices and a 41.66 % increase in β-turns in the PPI-AG (1:1) complex at pH 4.5 after 10 min of CP treatment. Thermal analysis showed a 9.4 % decrease in stability for the PPI-AG (1:1) complex at pH 4.5, along with enhanced water-holding capacity. ITC revealed stronger exothermic interactions in treated samples at lower pH. Overall, CP treatment improved the physicochemical properties of PPI-AG complexes.