Interface rheology of structured food

Abstract

Proteins are widely used to form and to stabilize the interfacial layers in multiphase systems, due to their surface activity and their ability to give high mechanical resistance to interfacial layers. In the food industry, animal proteins are largely employed with these functions, but, because of their tendency to give rise intolerances or, simply, for etic reasons, their use is becoming more and more limited. Vegetable proteins could be a good alternative to animal proteins, thanks to their good nutritional profile and complete amino acid profile, but their interfacial rheological properties are not widely known in order to evaluate their potential use in food products such as foams and emulsions. In this PhD work, the interfacial properties of vegetable proteins were studied and the results analysed by rheological models. Three different systems were investigated A/W interface, in particular, soy, hemp and brown rice proteins. The rheological analysis was performed in dilational and shear kinematics, using the pendant drop tensiometer and the interfacial rod magnetic field rheometer, respectively. The dilational analysis was performed either in static as well in dynamic condition. The static measurements allow evaluating the saturation concentration (CMC, critical micellar concentration) and the kinetic phenomena, while the dynamic measurements help to characterize the viscoelastic film at the interface. In particular, all the dynamic tests were performed at the CMC concentration, either the frequency sweep tests (in the linearity region) as well the stress relaxation tests (in the linear region, but far from equilibrium condition). The kinetic results were interpreted by the Ward- Torday and Graham and Phillips equations, while the William Watts and the Scott Blair models were employed for the relaxation experiments. Finally, vegetable emulsions were obtained and optimized and the use of a polysaccharide was necessary for stabilising them. The study of the emulsions was carried out with the help of microscopy and drop diameter distribution. Additionally, measurements of ζ-potential and flow curve tests were also performed to characterize the system The results showed that the vegetable proteins show comparable mechanical properties and good surface activity similar to the animal proteins (such as casein or lactoglobulin), confirming them excellent substitutes in a lot of food systems