Phase separation behavior and structural analysis of ovalbumin–gum arabic complex coacervation

Phase separation behavior and structure between ovalbumin (OVA) and gum arabic (GA) were investigated at pH 1.5–6.5; 2:1 OVA:GA mixing ratio, total biopolymer concentration 0.05 wt%. Soluble and insoluble complexes were observed as a function of pH. The biopolymers particles had a tiny diameter (d ≤ 500 nm) at pH above 4.0 or below 2.5, and increased sharply at pH 4.0 together with the turbidity under the same conditions. As the biopolymers mixing ratios increased from 1:3 to 24:1, critical pHs shifted towards higher pH. However, monovalent ions had a same influence on OVA–GA complex formation; the divalent cations reduced the formation of complex compared with same concentration monovalent ions. Second-derivative UV spectra and intrinsic fluorescence results indicated that the unfolding of the tertiary conformation was induced by GA, and more tryptophan residues were buried inside the OVA protein after complexation.