Effect of salt on the inter-relationship between the morphological, emulsifying and interfacial rheological properties of O/W emulsions at oil/water interface

The role of salt in oil-in-water emulsion is not widely studied, but relevant to food processing, formulation and sensory properties. The interaction between the emulsifier and salt could impart an important effect on the emulsion stability and rheology. This present study aimed to determine the interfacial rheology of oil-in-water emulsions that were stabilized by different salts and affected by the different emulsifiers that promote the interfacial layer. In addition, this study intended to investigate whether the droplet size and zeta potential functioned as contributing parameters. Two salts (sodium chloride-NaCl and calcium chloride-CaCl2) and three emulsifiers (lecithin, mono-diglycerides, sodium steoryl-2-lactylate) were chosen to select appropriate combinations for oil-in-water emulsions. The relationship between the interfacial properties and the O/W emulsion stability in the presence of salt was assessed by both optical microscopy and visual observation of phase separation throughout the storage. As a result, it was found that the interfacial storage (G(i)') and loss modulus (G(i)'') values were dependent on the frequency. This result suggested that the oil/water interfaces support the conformational reconstruction of emulsifier changes to take advantage of improved hydrophobicity which results from the frequency dependence of the surface modules. The stability of emulsions prepared with the presence of CaCl2 was found to be higher than the emulsions prepared with NaCl which can be attributed to the counter ions effects of the CaCl2. The steady, dynamic and interfacial rheological measurements were consistent with zeta-potential, creaming and morphological observations. The results of this study also demonstrated that the interfacial rheology data might be predictive of emulsion stability and CaCl2 salt will increase the stability of the product with the different emulsifiers in the food formulations.