The effect of Persian gum and thermal process on the properties of emulsion stabilized by whey protein concentrate

Many food products are comprised of an emulsion gel structure in which emulsion droplets are dispersed within a gel network. Formation of a stable emulsion which is later turned into a gel using processing techniques including heating, acidification or enzyme assisted-clotting is a crucial stage in the production of an emulsion-gel system. In the present study the influence of various concentrations of whey protein concentrate (3-8% w/w) and water soluble fraction of Persian gum (0.3-0.6% w/w) on the quality attributes of oil-in-water emulsion prior and after heat treatment (at 90 oC for 30 min) was evaluated. To this end, changes in the zeta potential, size of droplets, rheological behaviour of emulsions and also their microstructure were investigated. The results showed that increasing the concentration of whey protein concentrate in the system reduced the size of the emulsion droplets. On the other hand, the addition of 0.6% soluble fraction of Persian gum led to larger droplets. More over, heating emulsion samples resulted in a rise in the size of droplets and broadened their size distribution curves. However, Persian gum at lower level (0.3%) was found to considerably increase the stability of emulsion against heat. The viscosity of emulsion was shown to be greatly dependent on the soluble fraction of Persian gum concentration and dramatically increased upon heating which was attributed to depletion flocculation and protein aggregation. In addition, all samples exhibited Newotonian behaviour before and after heat treatment except at higher proportions of whey protein concentrate and Persian gum, which changed to shear thinning following heating. These findings confirm the capability of Persian gum for production of heat stable emulsions which may find various applications in food formulation such as Emulsion-gels.