BACK EXTRUSION RHEOLOGY FOR EVALUATING THE TRANSITIONAL EFFECTS OF HIGH PRESSURE PROCESSING OF EGG COMPONENTS

In this study, a back extrusion concept was used to evaluate the rheological properties of egg components treated by high pressure processing. Rheological properties, such as viscosity index (?) and apparent elasticity (E-a) of egg components, were evaluated using a central composite design with three independent variables included at five levels. The variables used were high pressure (350-550MPa), treatment time (10-20min) and temperature (15-35C). Apparent viscosity was also evaluated using a conventional rheology, using a parallel plate rotational viscometer. Viscosity index and apparent elasticity of various egg components were found to increase significantly (P<0.05) with an increase in treatment intensity. A relationship between apparent viscosity (rheological) and viscosity index (textural properties) was established. It revealed positive correlations for all egg components (egg white, egg yolk and whole liquid egg) with R-2 values higher than 0.95. Practical ApplicationsTextural/rheological characteristics play a significant role in determining the functional properties of whole liquid egg, egg white or egg yolk. Liquid foods are usually characterized by conventional viscometry and solid foods by their texture. The transition between liquid and solid covering the semi-solid consistency poses measurement problems for both techniques. Back extrusion rheology can be used to bridge the gap between the two. High pressure processing allows the liquid egg components to be transformed from liquid to a gel-like to a solid consistency, depending on the applied pressure level, temperature and time. Hence, back extrusion rheology is ideally suitable for studying texture formation in egg products during high pressure processing.