Physical and flow properties of d-limonene-in-water emulsions stabilized with whey protein concentrate and wild sage (Salvia macrosiphon) seed gum

•WSG could be useful in industrial applications as a new source of hydrocolloid.•Addition of SSG will enhance the stability of O/W emulsion containing whey protein concentrate.•Electrostatic repulsion occurred between protein covered oil droplets and gum molecules.•Interfacial tension of WPC was affected and decreased in the presence of wild sage seeds gum.•SSG-WPC emulsions' flow behavior was following the Herschel-Bulkly model.

The effect of varying concentrations of whey protein concentrate (WPC, 5-15% w/v) and wild sage seed gum (SSG, 0-0.3% w/v) on interfacial tension, zeta potential, physical stability, droplet size, flow properties and viscosity of d-limonene-in-water emulsions at pH 7 was investigated. The results indicated that the addition of SSG had no significant effect on zeta potential while the interfacial tension decreased with increasing gum concentration. For freshly prepared emulsions, the mean diameter of droplets slightly decreased as gum concentration increased from 0.0% to 0.3%. In contrast, protein concentration in the range of 5-15% showed no particular effect on the size of droplets. Storage of samples for a period of 4 weeks resulted in an increase in the size of droplets. This was substantially noticeable for the emulsions containing no SSG and negligible for those prepared with 0.3% SSG and 15% WPC. The presence of SSG in these emulsions increased the emulsion stability indices, evidently because of the higher viscosity it imparted to the aqueous phase. The emulsions containing only WPC showed Newtonian behavior, while those consisting of both protein and gum exhibited shear thinning characteristics. Various time-independent rheological models were examined to fit the experimental data; of which Herschele-Bulkley model was found to be the best model to describe steady shear flow behavior of these emulsions.