# Critical Review of Techniques for Food Emulsion Characterization
## 3 Techniques for Emulsion Characterization
### Rheological Analysis of Emulsions  
Investigating the rheological properties of emulsions provides insight into their behavior and stability. The complex interplay between stability and time-dependent changes in the rheological properties of emulsions influences their quality and functionality in various applications [116]. Understanding the thixotropic behavior, viscoelastic properties, and shear thinning behavior of emulsions is essential for product formulation and development, achieving the desired functional attributes, and optimizing emulsion performance at different stages of manufacturing, processing, packing, and storage. Characterization of the rheological properties of emulsions plays a fundamental role in predicting their response to external conditions, such as pressure, temperature, centrifugal force, applied to emulsions during technological operations, such as mixing, pumping, pouring, leveling, etc. [117]. Furthermore, the rheological properties of emulsions allow for monitoring their stability over time, which directly translates to their shelf-life. Quantitative analysis of emulsion rheological properties provides also important information about their visual and sen sory properties, such as appearance, texture, creaminess, consistency, and mouthfeel [118], which strongly influence the acceptance of commercial formulations by consumers and their preferences when choosing products. Rheological analysis of emulsions aims to determine the deformation and flow properties of emulsions under different conditions. The key parameters that determine the rheology of emulsions are the chemical composition and rheological properties of the continuous and dispersed phases, phase volume ratio, the structure of the emulsion including droplet size, concentration and distribution, droplet characteristics, such as deformability, internal viscosity, and inter-droplet interactions (e.g., steric interactions, electrostatic repulsion, and van der Waals attraction) [44], elasticity and composition of the interfacial layer (including concentration and type of the emulsifier), as well other colloidal interactions within the emulsion system. Emulsions vary greatly in terms of their rheological properties, from low-viscosity Newtonian liquids such as milk, through non-Newtonian, shear-thinning liquids that become less viscous under shear stress [119], to shear-thickening formulations, whose viscosity increases under shear stress, such as salad dressings, mayonnaise or creams. Flow curves offer important insights into the rheological behavior of emulsions. They depict the correlation between shear stress and shear rate, aiding in comprehending the flow characteristics of emulsions and defining their viscosity and shear thinning behavior. Therefore, flow curves can indicate whether the emulsion displays Newtonian or non-Newtonian behavior, Additionally, flow curves help define emulsion resistance to flow, showcasing its capability to maintain structure under varying shear conditions, which is essential for establishing suitable processing conditions [119]. The rheological properties of emulsions are largely dependent on the nature and characteristics of the continuous phase, including its chemical composition, pH, and viscosity [120]. The viscosity of the continuous phase has a major impact on the gravitational separation of the emulsion [121]. For example, a more viscous continuous phase can hinder droplet movement, thereby inhibiting the creaming or sedimentation processes [88]. At the same time, lower mobility of the droplets may promote flocculation or coalescence, leading to increased instability of the emulsion. The rheological properties of emulsions can be altered by adding polymers or hydrocolloids, such as thickeners and texture modifiers (e.g., pectin, modified cellulose, gum arabic, corn fiber gum, modified starch, polysaccharide-protein complexes, etc.) [122].