Separation of ovomucin from duck egg white and its “acid-tight /alkali-loose” self-supporting gel properties under different pH

Ovomucin is a key component in maintaining the viscous nature of egg white and has vast potential in the utilization of food industry. The objectives of the study were to determine the effect of different pH on the extractability and gel properties of ovomucin. After removing lysozyme through ion exchange, the diluted duck egg white was acidified to a narrow pH range (4.50, 4.75, 5.00, 5.25, 5.50, 5.75 and 6.00) to precipitate ovomucin. By comprehensive study of purity, yield, and convenience of large-scale preparation, 4.75 was chosen as the optimal pH to extract ovomucin with the highest purity of 85.17 ± 2.31% and a compromised yield of 4.60 ± 0.06 mg/g duck egg white. A series of self-supporting gels were prepared with freeze-dried ovomucin powder at room temperature upon rehydration and centrifugation, and the gels properties were highly associated with pH. Gel formed around pH 5 was the aggregate of natural globular proteins with lowest hydrophobicity and electrostatic interaction, relatively dense structure and high water-holding capacity (WHC). Stronger acidic conditions disrupted the disulfide bonds and formed a rougher spherical aggregate. Under alkaline conditions, however, the protein gradually unfolded and broke into linear basic polypeptides, thus a porous three-dimensional network was formed. Overall, this study provided insights into the formation mechanism of the “acid-tight/alkali-loose” ovomucin gels, and introduced a potential candidate for the development of bioactive substance delivery materials.