Effect of Chemical Modifications on Some Physicochemical Properties and Heat Coagulation of Egg Albumen

Egg albumen was modified with succinic anhydride and a water-soluble carbodiimide, 1-ethyl-3(3-dimethylaminopropyl) carbodiimide. The chemically modified proteins exhibited only minor conformational changes, but were altered in their responses to heat treatment. Heat-induced coagulation was retarded by both modifications suggesting that thermocoagulation requires a balanced electrostatic attraction between protein molecules. Hydrophobicity measurements and pH-titration data suggest the involvement of hydrophobic and ionic interactions in heat aggregation and gelation of egg white proteins. The soluble fraction of the heat-coagulated proteins contained mainly monomers, while under conditions where a gel or coagulum was not formed, the heat-treated egg albumen solutions contained high M.W. soluble aggregates. A scheme for the thermal coagulation of egg albumen is proposed.