Effects of shear rates on rheology, foaming properties and protein structure of egg white: structure-function relationships

The transformation of shell eggs into safe liquid, frozen or spray-dried egg white with extended shelf life requires many technological operations that result in modifications to the egg white’s functional properties. During these processes, shear rates underwent by egg white may be responsible for part of the loss of its functional properties. The present study was aimed at measuring the effects of a wide range of shear rates (from 0.1s-1 to 36000s-1 during 10 minutes) on egg white’s rheology, foaming properties and protein structure. Results highlighted three ranges of shear rates leading to different behaviour of egg white: very low shear rates (0.1s-1), low to medium shear rates (from 1 to 1000s-1) and high shear rates (over 1000s-1). At very low shear rates, egg white viscosity increased during the first few seconds. This led to a better foam stability, which was put down to protein unfolding. Mediumsheared egg white did not show any significant variation of its rheological properties and foaming capacity, compared to non-sheared egg white. Nevertheless, compared to low-sheared egg white, its viscosity, consistency and thixotropic behaviour decreased as well as protein surface hydrophobicity and foaming capacity whereas foam stability increased. These results were put down to the disruption of ovomucin-lysozyme complex as well as protein aggregation. High-sheared egg white (over 1000s1) tended to a Newtonian behaviour. It showed a strong increase of its foaming capacity and of its protein surface hydrophobicity. A multivariate factorial analysis highlighted correlations between rheological measurements, foaming properties and protein structure.