Rheological and structural properties of ovomucin from chicken eggs with different interior quality

Ovomucin is hypothesized to be responsible for the gel-like nature of egg white. However, few investigations have revealed the rheological property and conformational alterations of ovomucin from eggs with different interior quality. In this study, ovomucin was isolated from eggs with different Haugh unit (HU) values, ranging from 80 to 30 as a result of storage. The viscoelasticity and structural characteristics of ovomucin were analyzed using rheology, DLS, fluorescence, CD and FTIR spectroscopy. Rheological data revealed a significant decrease in the viscosity and elastic modulus (G') of ovomucin gel with decreasing HU value. The same trend was observed in the ovomucin content. The particle size distribution results showed the smaller average particle size and wider distribution range of the ovomucin from low HU eggs. When the HU decreased from 80 to 64, the blue shift and disappearance in infrared absorption peaks at 800-1200 cm(-1) confirmed the dissociation of glycosidic bond in ovomucin. Infrared and CD spectroscopic results demonstrated that the ovomucin undergoes a transition from intermolecular beta-sheet and alpha-helix structure to random coil structure when HU decreased from 80 to 64, and the stretched protein re-forms an ordered secondary structure such as beta-turn when HU further decreased from 53 to 30. There was an intermediate form in the secondary structure of ovomucin from eggs with HU between 64 and 53, indicating that the conformational transition of ovomucin does not fit the simple two-state mechanism. Zeta potential and hydrophobicity measurements further confirmed the existence of intermediate state.