Egg white-based strong hydrogel via ordered protein condensation

Despite the well-known thermal gelation property of egg white and its wide use in the food industry, the applications of gelled egg white in materials science are limited owing to the brittleness caused by the network structure of randomly associated denatured proteins. In this study, a gel material with high mechanical strength was fabricated from crude egg white proteins. Fluid materials containing orderly condensed proteins at regular intervals were prepared by addition of ionic surfactants to an egg white protein solution. The initiation of the heat denaturation of proteins from this ordered state with spatial confinement resulted in the formation of hydrogel materials with high mechanical strength. The maximum compressive fracture strength of the fabricated egg white-based hydrogel was 34.5 MPa, which is 150-fold higher than that of gelled egg white prepared by boiling and comparable to that of strong chemically synthesized hydrogels. Chemical modification of sulfhydryl groups of proteins and treatment with a denaturant revealed that denatured polypeptide chains were covalently linked by disulfide bonds and non-covalently associated; these findings showed that the high mechanical strength of our material is due to the synergic effects of both covalent and non-covalent networks. A high-strength material made from egg whites has been developed by researchers in Japan. Gels made from the whites of hen eggs are prominent examples of materials built from proteins, but brittleness limits their practical applications. A possible explanation for this mechanical weakness is that the gel contains a random network of thermally denatured proteins, which creates an inhomogeneous material. Now, Tatsuya Nojima from the Tokyo Institute of Technology and Tomokazu Iyoda from Doshisha University have shown that a surfactant can order egg-white proteins and improve the mechanical properties of the resulting gel. They added an ionic surfactant to an egg-white protein to produce a fluid with proteins orderly packed at regular intervals. The resultant material has maximum compressive fracture strength 150 times greater than that of gelled egg whites created by boiling. High mechanical strength hydrogel material was fabricated from egg white proteins. Egg white proteins were condensed at a regular interval with ionic surfactants and gelled by heating. The maximum compressive fracture strength was 34.5 MPa, which is 150-fold higher than that of boiled egg white. The high strength is due to the synergic effects of both covalent and non-covalent networks.