# Critical Review of Techniques for Food Emulsion Characterization
###### Abstract  
Emulsions have garnered significant attention within a variety of industries, including pharmaceuticals, food production, and cosmetics. The importance of emulsions across these sectors is attributed to their versatility and unique properties, such as increased interfacial area and the ability to deliver compounds insoluble in water or to mask the flavor of unpalatable ingredients. A comprehensive and precise assessment of the physicochemical properties, structural features, and stability of emulsions is an indispensable phase in the pursuit of new formulations and the improvement of manufacturing protocols. The characterization of emulsions encompasses an array of methodologies designed to determine their attributes, such as droplet size, distribution, concentration, surface charge, and others. In this review, we explore the techniques most frequently used to characterize emulsions and critically assess the significance each method holds in understanding the behavior and predicting the stability of emulsions. We elucidate the basic principles of these methods while emphasizing what information can be gathered from them, and how to effectively interpret this information to optimize the properties of emulsions, crucial from the standpoints of food and other industries, such as long-term stability and easy processing. food analysis; analytical techniques; droplet size; microstructure; stability; rheology; zeta potential; DSC; Raman spectroscopy; photon density wave spectroscopy; texture; oxidation; in vitro digestion +
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Analysis of rheological properties is another indispensable step in the evaluation of emulsions in terms of their manufacturing efficiency and product performance [13; 14]. Determining the optical properties of emulsions, including transparency and turbidity, is crucial for applications requiring optical clarity [15]. Further details of emulsion properties can be revealed by zeta potential analysis, which offers insight into the electrostatic forces governing droplet behavior [16], which are key factors affecting the stability of emulsions [17]. Another crucial aspect of emulsion dynamics is heat exchange during phase transitions and crystalline transformations [18]. These features can be examined by differential scanning calorimetry (DSC). DSC is particularly useful in tracking crystallization and melting processes in emulsions, which are closely linked to their viscosity, droplet size, and density [19]. One of the primary focuses in analyzing the properties of emulsions is their chemical composition. Emulsion composition can be qualitatively and semi-quantitatively assessed by Fourier Transform Infrared (FTIR) spectroscopy [20]. This technique allows the identification of functional and structural groups responsible for both chemical and physical aging, all while preserving the internal equilibrium of the emulsion. FTIR has proven instrumental in examining thermal degradation processes within oils, providing insights into the structural alterations occurring as the emulsion matures [21]. Evaluation of emulsions using _in vitro_ digestion models has become another valuable tool for emulsion characterization, especially in the food and pharmaceutical sectors, where there is a growing interest in understanding and controlling the digestion of emulsified lipids [22]. _In vitro_ models enable the assessment of emulsions as delivery systems for non-polar lipids, vitamins, nutraceuticalals, and other therapeutic compounds within specific gastrointestinal tract regions [23; 24]. Despite the widespread use of emulsions across different industries, the manufacturing and storage of emulsion-based formulations still face challenges related to lipid oxidation. The susceptibility to oxidation is intensified within emulsions due to their complex composition, increased interfacial area, and potential exposure to oxidative stress during emulsification.