EFFECT OF DROPLET–MATRIX INTERACTIONS ON LARGE DEFORMATION PROPERTIES OF EMULSION‐FILLED GELS

ABSTRACT The aim of this work was to identify the effect of droplet–matrix interactions on the large deformation properties of emulsion‐filled gels. A study was carried out on the behavior in compression of gelatin, whey protein isolate (WPI) and κ ‐carrageenan gels containing emulsions stabilized by different emulsifying agents (WPI, WPI aggregates, lysozyme, polyoxyethylenesorbitan monolaurate [Tween 20]) to control droplet–matrix interactions. For gelatin gels, emulsions stabilized with WPI and lysozyme induced an increase of the modulus, while emulsions stabilized with Tween induced a decrease of the modulus. It was concluded that in the first two cases, the oil droplets were bound to the gel matrix and that in the latter case the oil droplets were unbound. For WPI gels, emulsions stabilized with WPI aggregates, lysozyme and low concentration of Tween induced an increase of the modulus (bound droplets). The modulus variations observed for κ ‐carrageenan gels were mainly related to interactions between κ ‐carrageenan and the emulsifying agent present in the aqueous phase. Theories based on the effect of the oil content on modulus satisfactorily fitted the trend of the experimental results, both for bound and unbound droplets. The fracture strain decreased with increasing oil concentration for droplets bound to the matrix and remained constant for unbound droplets, while the fracture stress was unaffected by bound droplets and decreased in the case of unbound droplets. Theories describing the effect of filler content on fracture strain and stress failed to predict the experimental results. This was attributed to the small size of the oil droplets of the emulsions used in this study, which was similar to the size of the inherent defects present in the gel network. PRACTICAL APPLICATIONS This work deals with the mechanical properties of emulsion‐filled gels with different matrices and with different interactions between oil droplets and gel matrix. The effect of different interactions on the Young's modulus and the fracture properties of the gels is presented. Furthermore, the usefulness of several theories for the prediction of these properties is discussed. The gel systems studied resemble real food systems. Therefore, the obtained knowledge will enable the industry to engineer products with desired mechanical properties. This will make the process of new product development more efficient.