Extraction-dependent responses to pulsed electric field (PEF) pretreatment: A multi-analytical characterization approach for semi-refined flaxseed extracts

The response of plant materials to pulsed electric field (PEF) pretreatment followed by extraction, in terms of structural and compositional outcomes, is more complex than conventionally understood. This study investigated semi-refined flaxseed extracts (SRFE) prepared using PEF (0-534 kJ/kg) followed by either alkaline or water extraction, based on a multi-analytical characterization approach. Scanning Electron Microscopy (SEM) revealed opposing morphologies: alkali extraction produced smoother surfaces, whereas water extraction increased roughness and fragmentation at 534 kJ/kg. Differential scanning calorimetry (DSC) showed a U-shaped thermal response, with denaturation temperatures initially decreasing before partially recovering at 534 kJ/kg. The effect of PEF on protein extraction was dependent on both energy input and the extraction medium. When compared to the control, the measurable protein content decreased by 21.8% with alkaline extraction at 534 kJ/kg but increased by 14.2% with water extraction at 347 kJ/kg. At maximum PEF energy input, the total phenolic content increased by about 18%, accompanied by a 63–68% increase in arabinoxylan across both extraction media. Fourier-transform infrared (FTIR) analysis indicated contrasting α/β ratios from control to 534 kJ/kg for alkali extraction (0.96→1.44) compared with water extraction (1.75→1.12). Multivariate analysis confirmed synergistic interactions between PEF and extraction media. Remarkably, PEF-treated SRFE obtained by water extraction exhibited characteristics similar to those of untreated SRFE obtained by alkali extraction, indicating that convergent, gentler processing routes can achieve compositional and structural features comparable to those of conventional methods.