Denaturation of Spray-dried Egg Yolk During Processing and Storage

Abstract

Egg yolk powder is industrially produced by spray-drying fresh raw egg yolk separated from shell eggs. Stress due to heat and dehydration causes denaturation of egg yolk proteins, so it largely affects the quality level of the resultant dried powders. In this study, denaturation kinetics of dried egg yolk powder were measured under isothermal and iso-humidity conditions. The denaturation level was evaluated by using color index, viscosity values of the slurry (made from the dried powder dispersed in water) and the agglomerated particle sizes. Fresh egg yolk was spray-dried and the resultant quality levels of the dried powders were evaluated in the same manner. Some of these quality factors would not simply relate with the temperature and RH. It was suggeted from the kinetic parameters and the spray-drying experiments that the residence times of products in the specific parts of a drying system (e.g. atomizer, chamber, pipe for transport, collector etc.) would have critical impacts on the product qualities. The kinetic parameters predicted that even under a relatively low RH conditions, a rate of a quality change would significantly increase when products are subjected to higher temperature above threshold.