Interfacial behaviour of crayfish protein isolate

The interfacial behaviour of a crayfish protein isolate (CFPI) produced as by-product from the food industry has been studied at the air–water surface at two pH values (2 and 8). An analysis of the surface pressure and interfacial shear behaviour has been carried out as a function of CFPI content for the two mentioned pH values. The results indicate that CFPI shows higher surface pressure, smaller aggregates and higher interfacial viscoelasticity at pH 8 than at pH 2, being highly dependent on CFPI content. In fact, a transition from fluid-like behaviour to a gel-like behaviour have been obtained by increasing the protein content. These results are in agreement with the higher solubility and z-potential values and the longer emulsion stability found under alkaline conditions. Furthermore, usage of highly sensitive interfacial shear techniques, such as the magnetic rod interfacial stress rheometer or the double wall ring, both of them providing rather coincident results, has proven to be highly useful to study the viscoelastic properties of CFPI interfacial films at levels that cannot be detected by other methods.