A thermoreversible emulsion gel based on sodium caseinate

Thermoreversible gelation is demonstrated for a milk protein-based oil-in-water emulsion system. The emulsifying agent is sodium caseinate with a controlled amount of ionic calcium added (15-30 mM, depending on the pH). On heating to 30-40 degrees C, a concentrated liquid-like emulsion is converted into a flocculated emulsion gel that supports its own weight. Small-deformation rheology gives quantitative confirmation of the large increase in viscoelasticity on heating over an interval of just a few degrees in the range 35-45 degrees C (depending on the pH). The emulsion gel 'melts' again slowly on cooling, and the return to the original low-viscosity state is accelerated by stirring. As followed viscometrically, the thermoreversible behaviour shows good reproducibility on repeated temperature cycling at different pH values in the range 5.5-6.8. The main driving force for the gelation is presumably an increase in the strength of hydrophobic interactions with increasing temperature. (C) 1999 Elsevier Science Ltd. All rights reserved.