Deformation and fracture of emulsion-filled gels: Effect of gelling agent concentration and oil droplet size

Abstract

The effect of the ratio between the modulus of the oil droplets and that of the gel matrix (varied by changing gelling agent concentration and oil droplet size) on the large deformation properties of gelatine, κ-carrageenan and whey protein isolate (WPI) gels was studied at different compression speeds. The effect of gelling agent concentration and oil droplet size on strain-dependency of modulus and viscoelastic properties was also studied. An increase in the concentration of gelling agent resulted in denser gels with more bonds between structural elements. This induced an increase of both Young's modulus and fracture stress for all gels. With increasing gelling agent concentration, polymer gels (gelatine and κ-carrageenan) became less strain-hardening, and the particle gels (WPI) even became strain-softening. The effect of a decrease in the oil droplet size on the Young's modulus was generally according to the Van der Poel theory, unless when the oil droplets were aggregated. Moreover, a decrease in oil droplet size induced a decrease of the fracture strain in gels with non-aggregated bound droplets. The extent of these changes was shown to depend on the gelling agent concentration. The effect of a decrease of the oil droplet size on other fracture parameters and in other gel systems was minor. With decreasing oil droplet size gelatine gels with unbound droplets and WPI gels became more viscous and less elastic.