Interfacial rheology, protein film

Murray, B.S., Dickinson, E. (1996). Interfacial rheology and the dynamic properties of adsorbed films of food proteins and surfactants. Food Science and Technology International (Japan), 2, 131-145. 

Pure oil/protein solution systems The Interfacial Displacement Tensiometer was used to examine the effect of additives known to promote an appreciable interfacial rheology. The systems selected were Toluene/a-lactalbumin (100 ppm), toluene/BSA (100 ppm), and nonane/BSA (100 ppm) these systems were expected to produce highly visco-elastic interfacial films. The BSA solution when displaced by either toluene or nonane (see Figure 11) gave rise to pressure jumps on the I.D.T. traces at points equivalent to entry and exit of the narrower capillary. These peaks indicate an increased resistance to displacement of the interface associated with its deformation and changes of extent. The maximum pressures are considerably in excess of those given by the pure oil/water reference system, also shown in Figure 11. 

Adsorbed protein molecules interact at the interfaces to form viscoelastic films. The viscoelastic properties of protein films adsorbed at fluid interfaces in food emulsions and foams are important in relation to the stability of such systems with respect to film rupture and coalescence. Interfacial rheology techniques are very sensitive methods to measure the viscoelastic properties of proteins, thereby evaluating the protein-protein or protein-surfactant interactions at the interfaces. There was an excellent review about the principal and methods of interfacial rheology [17]. 

It has long been argued that interfacial rheology, namely interfacial viscosity and elasticity, play an important role in emulsion stability. This is particularly the case with mixed surfactant films (which may also form liquid crystalline phases) and polymers such as hydrocolloids and proteins that are commonly used in food emulsions. 

While dilatational rheology plays an important role in short-term stability of dispersions shear viscosity may contribute appreciably to the long-term stability (Murray and Dickinson, 1996 Murray, 1998, 2002). The shear characteristics of the interfacial film are governed by the composition and structure of the adsorbed material. In addition, surface shear viscosity is a very sensitive technique to analyze the competitive adsorption of protein and water-soluble LMWE at the air-water interface (Murray and Dickinson, 1996 Murray, 1998, 2002 Bos and van Vliet, 2001). 

The behavior of proteins at interfaces influences the formation of foams and emulsions (32). Stabilization of foams and emulsions depends, to a great extent, on the formation, rheological, and mechanical properties of the interfacial film ( ). Factors which ensure optimum film properties in simple systems may retard film formation or cause destabilization in foams or emulsions (3 ) for example, many rheological properties of films are maximum in the isoelectric pH range of specific proteins, yet most proteins have minimum solubility in this pH range (34). Thus, environmental and processing factors which... 

---