# Critical Review of Techniques for Food Emulsion Characterization
## 2 Emulsion Formation and Stability
Polydispersity enhances flocculation, as differences in creaming rates between small and large droplets cause them to come into proximity more often compared with monodisperse systems. The cream layer formed towards the end of this process actually constitutes a concentrated floc. The third process leading to emulsion separation is Ostwald ripening. During Ostwald ripening, smaller droplets are incorporated into larger ones because of pressure differences between the droplets and the continuous phase, as well as differences in the solubility of unevenly sized droplets. In polydisperse emulsions, smaller droplets exhibit higher Laplace pressure compared to larger drops. Small droplets also have higher solubility in the continuous phase and therefore tend to be included in the larger droplets. Ostwald ripening occurs due to the diffusion of the dispersed phase through the continuous phase, involving a continual exchange of matter. As a result, there is a continuous transfer of the dispersed phase from small to large droplets, leading to a gradual growth of larger droplets and the diminishment of smaller ones. This disproportionation leads to a reduction in the total number of droplets within the population. The rate of Ostwald ripening is influenced by the solubility of the dispersed phase in the continuous phase. Higher solubility results in faster Ostwald ripening [41]. Therefore, this separation process can be minimized by selecting a dispersed phase that exhibits low solubility in the continuous phase [42]. As mentioned above, creaming involves the movement of the dispersed phase to the upper layer of the emulsion. It results from density differences between oil and water phases, leading to droplets rising to the surface. The separation process that occurs through a similar mechanism is sedimentation. Sedimentation is commonly observed in water-in-oil emulsions, where heavier water droplets gather at the bottom. Creating or sedimentation can be prevented by employing a high-viscosity continuous phase or regulating both particle size distribution and dispersed phase density. The temporal evolution of emulsion separation is subject to multi-factorial influences, encompassing parameters such as emulsifier type and concentration, water-to-oil volume ratio, the incorporation of additives, like co-surfactants, polydispersity index, and the physicochemical attributes of the mixture constituents (including viscosity, density, and interfacial tension) [44]. Other determinants include polarity, ionic strength, and temperature. Emulsion stability characteristics can vary greatly, with certain emulsions designed for transient stability, while others demonstrate enduring stability, persisting for weeks, months, or even years [45]. The choice of emulsifier can greatly influence the stability and physicochemical properties of emulsions. Emulsifiers can be either ionic (positively or negatively charged), zwitterionic (carrying both positive and negative charges at neutral pH) [46], or nonionic. Ionic emulsifiers form a charged shell around droplets, causing electrostatic repulsion between them. The extent of repulsion depends on the emulsifier surface charge and ionization degree, which are strongly affected by emulsion pH and the presence of other charged species, like electrolytes [44]. This renders them sensitive to composition and pH, limiting their use to specific emulsion types. For instance, cationic emulsifiers perform well in low pH and neutral solutions but not in alkaline solutions, whereas anionic emulsifiers are better suited for alkaline emulsions. Nonionic emulsifiers, which contain large bulky non-charged polar groups in their molecules, are considered more universal as they can effectively stabilize different kinds of emulsions [44]. This is due to steric hindrance, which prevents droplet coalescence without being sensitive to changes in medium pH and composition. Therefore, most emulsions are stabilized by this kind of emulsifier (e.g., Pluronics 70, Tween-80, Span-80, Brij-30) [47].