Instability and partial coalescence in whippable dairy emulsions

Dairy emulsions must be stabilized by an adsorbed layer to prevent flocculation or phase separation during quiescent storage. In the production of products such as whipped cream and ice cream, however, a controlled destabilization or partial coalescence of the emulsion is needed during further processing to develop an internal structure of agglomerated fat, which favorably alters the texture and physical appearance of the product. Several requirements must be met to induce partial coalescence, including a partially crystalline emulsion (implying refrigerated temperatures for milk fat), a weak adsorbed layer, and usually the presence of air, agitation, or both. Milk fat that is homogenized in the presence of a blend of caseins and whey proteins normally produces an emulsion that is too stable to undergo partial coalescence. Thus, small molecule surfactants (e.g., monoglycerides, diglycerides, and polysorbates) are added to protein-stabilized emulsions to promote partial coalescence by displacing proteins from the surface, resulting in a reduced surface concentration. However, it may be possible to control the adsorbed protein layer, hence promoting partial coalescence without the use of such surfactants, by selectively homogenizing the emulsion in the presence of only those milk proteins that would produce an interfacial layer that would be weak yet sufficient to maintain stability of the emulsion during storage but not sufficient to maintain stability during a whipping process.