Changes in gel characteristics of egg white under strong alkali treatment

Changes in gel characteristics, such as rheological and textural properties, microstructures, and intermolecular forces, of egg white (EW) treated with strong alkaline solution were investigated. The viscosity of EW increased gradually in the pre-gel phase. After the gel was formed, the textural properties and microstructures became dynamically changeful. With continuous strong alkali treatment, the formed gel was destroyed and gradually collapsed. Changes in sulfhydryl (SH) group and disulfide (SS) bond contents suggested that oxidation and SH–SS bond exchange reactions rapidly occurred under strong alkali conditions. However, SS bonds were easily broken at very high pH. Selective protein solubility of EW gels indicated that more than half of the total bonds were ionic. Furthermore, one third bonds were SS. Approximately 10% of these bonds was hydrophobic interactions, and few hydrogen bonds were present. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles revealed that the proteins in the gel were degraded and aggregated by alkali treatment. Hence, ovalbumin was involved in the cross-linking of SS bonds rapidly promoted by alkali treatment, and also implicated in gel formation supported by various intermolecular forces, such as ionic bond and hydrophobic interactions.