Micronization-assisted pulsed electric field treatment on functional and structural modification of red pepper seed protein isolates.

Abstract

Background: Red pepper seeds are an underutilized source of plant proteins with functional potential, but their poor solubility and limited functionality restrict food applications. This study investigated the effects of micronization-assisted pulsed electric field (PEF) treatment on the structural, physicochemical, and functional properties of red pepper seed protein isolates (RPSPIs).

Methods: RPSPIs were subjected to micronization pretreatment followed by PEF treatment under different electric field strengths and processing conditions. The effects of combined treatment on surface hydrophobicity, turbidity, Free Sulfhydryl (SH) Content, particle size distribution, surface morphology, secondary conformation, thermal stability, solubility, emulsifying properties, and foaming characteristics were systematically evaluated. Structural modifications were characterized using Fourier-transform infrared spectroscopy (FTIR), fluorescence spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC).

Results: The combined treatment significantly impacted the functional properties, including zeta potential and particle size of RPSPI-treated samples, enhancing stability compared to control samples. The structural data revealed important molecular modifications, including enhanced SH^- content and reduced fluorescence intensity, suggesting that the structure partially unfolded. In addition, FTIR analysis combined with Amide I deconvolution demonstrated that MR and PEF treatments significantly altered the secondary structure composition of RPSPI, with changes in α-helix, β-sheet, β-turn, and random coil components. The combined MR-PEF treatment promoted greater protein conformational rearrangement, which was associated with improved dispersion behavior, and enhanced functional properties. SEM micrographs revealed significant changes and fragmentation, further supporting our findings. The XRD analysis revealed changes in crystalline structure and crystallinity, while DSC results demonstrated increased denaturation temperatures after treatment, indicating enhanced thermal stability of RPSPI. The combined treatments also had significant impacts on these structural changes, enhancing foaming capacity, solubility, and emulsifying properties and decreasing turbidity.

Conclusion: This study's findings add value to red pepper seed by-product and provide insight into novel processing methods for high-value plant protein components.