# Critical Review of Techniques for Food Emulsion Characterization
## 3 Techniques for Emulsion Characterization
### Raman Spectroscopy  
Raman spectroscopy offers an innovative approach to the analysis and characterization of emulsions and food structures. Falling under the umbrella of vibration spectroscopy, Raman spectroscopy exposes a sample to an intense light beam, typically generated by a laser. The resulting spectrum, capturing the Raman-active vibration modes induced in the sample's molecules, is obtained through the analysis of inelastically scattered photons [94]. The intricacies of the process involve an inelastic collision between incident photons and the molecules within the sample. Consequently, the vibrational or rotational energy of the molecules changes, causing a shift in the scattered radiation to a different wavelength, known as a Raman shift [180]. It is well established that specific chemical bonds (such as C=C, C-H, C=O, and others) produce distinctive Raman shifts, making Raman spectroscopy an effective technique for investigating molecular structures [181]. This technique stands out for its high precision, rapidity, and noninvasiveness. Emulsions, which are often water-based systems, might generate a broad water background signal when infrared spectroscopy is used. As the Raman signal of water is low (at least at low wavenumbers), the unsaturated C=C bonds, found in oils, have a strong and sharp Raman response, making Raman spectroscopy a perfect method for the analysis of emulsion systems [182]. Due to the excellent functionality of Raman spectroscopy, it can be applied in (i) monitoring or mapping the components, droplets, or structure of emulsions, (ii) measuring the formation and destabilization of emulsions, and (iii) monitoring the emulsion polymerization reactions or other types of reactions involving emulsions. In conjunction with other methods, this technique allows tracking of the changes occurring in the emulsion structure during fabrication, processing, and storage. A study by [PERSON] et al. [183] investigated the food-grade Pickering emulsions stabilized by ovotransferrin (OVT) fibrils using Raman imaging microscopy. They used the Raman intensity mapping of the emulsion droplets and confirmed the presence of OVT fibrils located at the interface of the droplet. Another study showed the effect of L-arginine addition on the increase of solubility and emulsification of myofibrillar protein, indicating a partial unfolding of emulsifier structure by Raman spectroscopy [184]. In general, the Raman method is used to compare the molecular structure differences between tested stabilizers at varied conditions. Identification of functional groups involved in maintaining emulsion stability can help to design emulsions with tailored functionalities. Raman spectroscopy can also serve as a valuable tool for monitoring the effects of emulsion processing conditions on its stability. A study by [PERSON] et al. [185] investigated oil-rich emulsions that were subjected to 1, 2, or 3 h of enzymatic hydrolysis. Raman data showed that, as the hydrolysis time increased, a decrease in emulsion stability was observed due to the protein aggregation _via_ SS bonds or lipid-protein interactions (Figure 13). Another study [186] reported the monitoring of emulsion polymerization reactions by Raman spectroscopy. Results showed that the instantaneous conversion and free monomer concentrations were better estimated by Raman spectroscopy than by the calorimetry method. Emulsion polymerization is a primary reaction in the polymer industry; therefore, the online control of the process is critical in providing closed-loop monitoring strategies that would allow the fabrication of polymers with defined microstructures. In the study by [PERSON] et al.