ABSTRACT
Many food products such as salad dressing, mayonnaise, and ice cream are foams and emulsions. Such dispersions are thermodynamically unstable. However, their stability may be enhanced by the adsorption of amphiphilic molecules to the surface of the dispersed phase [1,2]. These molecules generally fall in two classes: macromolecules, such as proteins, and low-molecular-weight surfactants, such as monoglycerides and phospholipids. Surfactants adsorb and orient at fluid-fluid interfaces and thus reduce the interfacial tension between the phases. Proteins form a condensed viscoelastic film of highly self-interacting molecules at the interface, which resists local deformation [3,4]. In contrast, surfactants form a fluid adsorbed layer in which adsorbed molecules can diffuse laterally toward regions of high surface tension conferring stability via the Marangoni effect [5]. Individually, the viscoelastic and Marangoni mechanisms are very effective at stabilizing foams and emulsions but are mutually incompatible. Low-molecularweight surfactants, because of their much lower molecular weight, pack more efficiently at the interface and thus reduce the interfacial tension to a greater extent than proteins [6]. On the other hand, intermolecular interactions between molecules of a low-molecular-weight surfactant are much weaker and develop ment of high mechanical strength is not possible [7]. For these reasons, both classes of molecules are used in food systems. This may cause a problem, as competition between the two mechanisms arises, leading to instability of the sys tem [8-26].
