Comparative Composition, Interfacial Properties, and Antioxidant Activity of Flaxseed Protein Isolates from Different...

The present study aimed to compare the composition structure, interfacial, and antioxidant activities of flaxseed protein isolates (FPIs) in different flaxseed varieties. The results showed that apparently intact protein bodies (PBs) were manifested as densely staining cytoplasmic inclusions with distinct boundaries and varying diameter ranges among different flaxseed varieties. Through alkali extraction with isoelectric precipitation, FPIs exhibited a relatively small and irregular lamellar strip structure with varying sizes and shapes packed with spherical particles in studied flaxseed varieties. The different composition structures of FPIs among studied flaxseed varieties were also obtained, involving the protein subunits' intrinsic fluorescence properties, secondary structures, and amino acid profiles. These structural differences also led to differential purities, aqueous solubility, dispersion properties, and surface charges. Moreover, the varying emulsifying and foaming properties of FPIs from different flaxseed varieties were also observed due to the formation of coarse lipid droplets (5~40 μm) and foams (20~100 μm) with the specific structure of the oil/gas-water interface and bulk aqueous phase. The retention of phenolic compounds into FPIs still displayed evident variety specificity from 323 to 478 mg/100 g and 210 to 347 mg/100 g, which definitely led to escalated antioxidant activities. Thus, FPIs from Longya 13# and Neiya 9# flaxseed varieties were screened for favorable emulsifying and foaming properties due to the balanced molecular rigidity/unfolding and interfacial adsorption/stabilization behavior.