Impact of a thermal treatment on the emulsifying properties of egg yolk. Part 1: Effect of the heating time

The denaturation degree of egg yolk (EY) protein was determined in dilute EY suspensions containing 20% fresh EY (w/w) as a function of the heating time (0-40 min.) at 74 degrees C. The impact of such a thermal treatment on the emulsifying properties of the EY was studied in a fluid oil-in-water (O/W) emulsion containing 30% oil (v/v). Heating of the EY prior to emulsification appeared to slightly increase the oil droplet size and to drastically decrease of the level of flocculation. It was also shown that the concentration of proteins in the interfacial film increases with increasing degree of EY protein denaturation, which is thought to be responsible for the change in the colloidal interactions between droplets. The increased steric repulsions due to the increased interfacial protein concentration could explain the decrease of oil droplet flocculation. The impact of such modifications on the rheological properties and creaming stability of the emulsions is discussed. (c) 2006 Elsevier Ltd. All rights reserved.