Enhancement of gel strength by application of thermal treatments in highly flocculated emulsions

Thermal-induced changes of the rheological behavior of flocculated emulsions through the optimization of in situ thermorheological treatments, as well as the effect that several compositional variables (oil fraction, egg yolk concentration or cholesterol reduction level) exert on the enhancement of gel strength, were investigated. With this aim, oil-in-water emulsions were prepared using a spray-dried egg product. Different temperature ramps under oscillatory shear and droplet size distribution measurements were carried out. An increase in temperature produces, first of all, an increase in the storage modulus up to a critical temperature, which depends on heating rate. Subsequently, a dramatic decrease in the viscoelastic functions occurs, due to emulsion breakdown. However, the application of upward/downward temperature cycles, setting the maximum temperature at 67 °C, avoids emulsion breakdown and yield significantly higher values of the rheological functions in comparison to those found with fresh emulsions, in spite of the thermal-induced droplet coalescence observed. The final values of linear viscoelastic functions and droplet size depend on the type of cycles applied, which are based on different heating rates or times at the maximum temperature, and emulsion composition.