The rheology of lupin seed (Lupinus albus ssp. graecus) protein isolate films at the corn oil–water interface

Lupin seed protein isolates adsorbed at the corn oil–water interface formed, after long ageing times, interfacial films with viscoelastic properties. The viscoelastic parameters of the films, derived by analysis of creep compliance–time curves, were markedly influenced by the aqueous phase protein concentrations, pH, ageing time and isolate preparation methods. Instantaneous elastic modulus, E₀(s), showed maxima at a certain concentration which probably corresponded to monolayer saturation coverage and at pH 5.5, i.e. near to its isoelectric point, where the protein molecules are in a more compact form than at other pH values. The full fat lupin seed protein fractions gave the highest viscoelasticity values under all conditions and this in turn have an effect on the corresponding emulsion/foam stability.