Phase separation behavior and characterization of ovalbumin and propylene glycol alginate complex coacervates

Ovalbumin (OVA) is the most abundant protein in egg white, but its application in food processing was limited because of its poor functional properties near isoelectric point. In this study, propylene glycol alginate (PGA) was used for the first time to form coacervate with OVA to solve this problem. The objective of this research was to investigate phase separation behavior and structural characteristic of OVA-PGA coacervates. Phase behavior transition during coacervate formation was carried out by turbidity, zeta-potential and appearance with the change of pH, NaCl concentration and protein/polysaccharide ratio R. At R = 2:1, the turbidity curve indicated that the soluble complexes and insoluble coacervate occurred at pH 4.78 (pH(c)) and 4.08 (pH(phi 1)), respectively. Specially, with increasing NaCl concentration, the turbidity decreased significantly. With increasing OVA/PGA ratio, the turbidity curve shifted to higher pH. The results of UV and fluorescence spectra demonstrated that the tertiary conformation of OVA was changed by PGA interaction. Besides, the Fourier transform infrared spectroscopy (FTIR) revealed that complexes were formed through the electrostatic interactions between the -NH3+ groups of OVA and -COO- groups of PGA. OVA-PGA coacervation resulted in structural change and improved OVA thermal stability. Consequently, these findings can make contribution to the development of OVA-PGA coacervates as the encapsulation of functional ingredients.