Interfacial, Emulsifying and Foaming Properties of Milk Proteins

Abstract

The emulsifying and foaming properties of milk proteins are amongst their most important functional properties (Morr, 1982; Mitchell, 1986; Doxastakis, 1989; Mulvihill and Fox, 1989; Phillips et ai., 1994; Damodaran, 1997) and the characteristics of most dairy products depend sensitively on how the milk protein fraction is organized at fat-serum and air-serum interfaces (Mulder and Walstra, 1974). Like all soluble food proteins, the caseins and the whey proteins exhibit high surface activity. The main thermodynamic driving force for protein adsorption at hydrophobic surfaces is the removal of non-polar side-chains from the unfavourable environment of the bulk aqueous phase (Dickinson et ai., 1988; Dickinson, 1989a; Dickinson and McClements, 1996). Both the caseins and the whey proteins have an especially strong tendency to adsorb at oil-water and air-water interfaces and to protect emulsions and foams against various physico-chemical mechanisms of instability. The relative effectiveness of different samples can vary substantially, however, depending on the exact protein composition, the molecular structures of the main individual protein monomers, the local solution environmental conditions, and the state of aggregation. In the case of milk proteins used as commercial ingredients, the state of aggregation is particularly strongly influenced by the prior processing conditions.