Covalent modification of flaxseed protein isolate by polyphenols and characterization of the structural and functional properties of the conjugates

This study investigated and characterized the covalent and non-covalent conjugation of flaxseed protein isolate (FPI) with a crude extract of flaxseed polyphenols (FP), flaxseed lignan-secoisolariciresinol diglucoside (SDG) and tea polyphenols (TP). Covalent conjugation using the alkaline method was found to result in a higher grafting efficiency compared with free-radical grafting. Fourier-transform infrared spectrometry, scanning electron microscopy and fluorescence spectrometry showed marked alterations in the secondary, tertiary, and surface structures of the FPI-polyphenol conjugates. In contrast, non-covalent binding did not affect the FPI conformation significantly. The FPI-polyphenol conjugates showed higher emulsifying activity and foaming ability than FPI, with the highest emulsification seen in the FPI-TP-A conjugate. Moreover, the antioxidant activities of FPI-polyphenol conjugates and the non-covalent mixtures were higher than those of FPI. These findings offer new research directions for the utilization of FPI and an effective method for the preparation of bioactive wall materials to encapsulate polyunsaturated lipids.