Covalent modification of flaxseed protein isolate by phenolic compounds and the structure and functional properties of the adducts.

Covalent modification of flaxseed protein isolate by phenolic compounds including flaxseed polyphenols, ferulic acid, and hydroxytyrosol was studied under alkaline condition and in the presence of oxygen. The structure and function of the adducts was evaluated. The extent of covalent reaction and the physicochemical characteristics of flaxseed protein isolate-phenolic adducts were found to depend on the structure of the phenolic compounds. The decrease in free amino, thiol and tryptophan groups and increase in molecular weight were different. Crosslinks were found in flaxseed protein isolate-hydroxytyrosol adducts while ferulic acid and flaxseed polyphenols were unable to crosslink flaxseed proteins. The thermal stability and antioxidative capacity of the adducts were higher than those of flaxseed protein isolate. The structural conformation and hydrophobicity of the adducts were also found to depend on the nature of phenolic compounds. These adducts can be used in food formulations as natural antioxidants, emulsifiers and encapsulating shell materials.