Consolidation of foams deriving from emulsions by temperature cycling (“tempering”)

We produce oil-in-water emulsions comprising almost totally crystallized droplets at T = 4 °C, stabilized by a mixture of proteins and low molecular weight surfactants. Foams are produced by incorporating air bubbles in the previous emulsions under intense stirring at low temperature (whipping process). The kinetic stability of the foams can be substantially enhanced by warming the systems immediately after whipping, and cooling them again. Owing to this treatment referred as temperature cycling or “tempering”, foams clearly stiffen and they can then be stored at 4 °C for several weeks without any visible structural change. In this paper, we investigate the origin of this consolidation. We follow the bulk rheological properties of foams during and after the tempering treatment. The storage modulus, G′, is significantly larger than the loss modulus, G″, reflecting the essentially elastic nature of the materials. G′ exhibits a dramatic increase when tempering is applied. The elasticity in whipped emulsions arises from the network of interconnected solid fat droplets. By using different techniques (differential scanning calorimetry (DSC), NMR, light scattering), we deduce that an increase of the network connectivity due to partial coalescence is the most probable cause for the elasticity and stabilisation gains obtained after tempering.