PHYSICAL STABILITY AND RHEOLOGICAL PROPERTIES OF PROTEIN-PROTEIN MULTILAYER O/W EMULSIONS
Multilayer emulsions have innumerous applications in food industry and their composition and properties can help stabilize oil droplets against aggregation caused by exposure to environmental stresses. This type of emulsion has been developed using the layer-by-layer technique, which consists of direct adsorption of an oppositely charged polyelectrolyte layer on a primary layer of charged emulsifier, as protein. This work aimed at evaluating the impact of interactions between globular-globular proteins or flexible-globular proteins on the stability and rheological properties of O/W emulsions. Whey protein isolate (WPI) (globular and negatively charged protein) and gelatin (flexible and positively charged protein) were deposited sequentially at concentrations from 0.5% to 1.5% on the surface of primary emulsions containing 5% of sunflower oil stabilized with either 0.5% gelatin or WPI, respectively, at pH 7. These systems were compared with a similar system formed by lactoferrin (globular and positively charged protein) and WPI. Droplet size, zeta potential, creaming index, microstructure and rheological behavior of these emulsions were studied. In the case of globular-globular interaction, the use of WPI in the second layer favored the emulsion stability. These results can be related to the high surface charge and small droplet size. For these stable emulsions, it was observed a Newtonian behavior and low viscosity. When the lactoferrin was used in the second layer, the droplet size increased for higher concentrations of the latter, which led to unstable emulsions with shear thinning behavior. In the case of globular-flexible interaction, there was an increase of droplet size during the storage, which led to slowly phase separation. From this data, it could be concluded that, to form a multilayer emulsion, it is better using a protein with the same main structure. These systems could be interesting for food applications, as encapsulation system requiring a slowly or controlled release of compounds.