Structural and gelling properties of dry-heating egg white proteins

Gel strength of dried egg white greatly increased by heating in the dry state at 80 degrees C. The structural changes responsible for the enhancement of gel strength were studied. Heat-induced gelation of dry-heated egg white in the presence of denaturing reagents resulted in a decrease of gel strength in the order SDS urea 2-mercaptoethanol. CD spectra revealed only little changes in the secondary structure of some egg white proteins upon dry-heating, except ovotransferrin. Proteolytic digestibility of ovalbumin and ovotransferrin increased progressively with an increase of dry-heating time, indicating enhancement of protein flexibility by such heating in the dry state. DSC thermograms showed that enthalpy of denaturation (delta H) of dried egg white was markedly decreased with an increase of dry-heating time. In parallel, the Gibbs free energy of unfolding in water (delta G) was also found to decrease at approximately the same rate as delta H. A good correlation was obtained between the decrease in delta H and the increase in gel strength of egg white proteins heated in the dry state