Effect of charge density of polysaccharide on self-assembly behaviors of ovalbumin and sodium alginate

Similarities and differences of assembly for ovalbumin (OVA) and two kinds of sodium alginate (SA1 and SA2) varying in charge densities (λ_SA1: λ_SA2 ≈ 2:1) were investigated. The assembly processes of OVA/SA mixtures were characterized by phase diagram, particle size, and microstructure. Two differences between OVA/SA1 and OVA/SA2 mixtures in the phase diagram were distinctly observed. First, due to the higher charge density of SA1, the strong interaction between OVA and SA1 caused only pH_φ1 to be recorded. A higher linear charge density of SA1 narrowed the pH_φ1-pH_φ2 range at ratios of 2:1 and 1:1. Second, OVA/SA1 complexes formed a coacervate with a relatively strong resistance to ion-induced shielding effects. This maintained the smaller size (tighter structure) with a larger number of complexes in the coacervate without 250 mM NaCl. The regulating polysaccharides with different charge densities could control the soluble region of complexes and endow various size or morphology of the coacervate assembled by proteins and polysaccharides.