Factors affecting the freeze-thaw stability of emulsions

Many food emulsions are frozen to provide long-term stability to the product or as a necessary part of the food itself (e.g., ice cream), but very often the thawed emulsion is significantly destabilized and sometimes completely broken down into an oily and an aqueous phase. The phase behaviour of the frozen emulsion and hence the potential stresses can be calculated from the composition of the aqueous phase. For example, a 20% o/w emulsion prepared with 10% sucrose in the aqueous phase when frozen to -20 degrees C about 85% of the aqueous phase has frozen to ice leaving the unfrozen phase concentrated to about 62% with respect to droplets and 67% with respect to sucrose. The high-volume fraction and expanding ice press the droplets together and the high sugar (and other solute) concentration can affect the interdroplet forces. A combination of these effects can lead to the membrane separating the droplets rupturing and is responsible for the coalescence seen on thawing. The published studies on freeze-thaw stability of emulsions are reviewed within the framework provided by the phase diagram calculations. (C) 2007 Elsevier Ltd. All rights reserved.