Conformational Modifications of α Gliadin and Globulin Proteins upon Complex Coacervates Formation with Gum Arabic as Studied by Raman Microspectroscopy

Abstract

As a molecular model of gelatin-free coacervates, complexes of pea globulin and α gliadin proteins with gum arabic prepared at different acidic pH values are studied using Raman microspectrometry. Raman spectra confirm higher content of β-sheets and random coils in pea globulin and dominating α-helical structures in α gliadin. For protein−gum arabic complexes, Raman data support the existence of specific pH conditions for optimal complex coacervation (pH 2.75 for globulin and pH 3.0 for gliadin¹), when (i) pH-induced conformational perturbations of free protein structure are the strongest and (ii) compensation of these perturbations by gum arabic is the most pronounced. Conformations implied in the protein−gum complexes are mainly β-sheets in pea globulin and α-helix in α gliadin. The role of electrostatic and non-Coulombic interactions (intermolecular hydrogen bonds) in stabilizing of protein−polysaccharide complexes is discussed in relation with the overall structure and the charge density profile of these two proteins.