## 3 Factors Influencing and Mechanistic Pathways in Egg Yolk Emulsification  
### Chemical Treatment  
#### 3.1.1 pH and Ionic Strength  
The emulsifying properties of egg yolk are intricately linked to the competitive arrangement of its components at the oil-water boundary and the structural dynamics of egg yolk particles. Proteins and phospholipids are the primary emulsifiers within egg yolk, with proteins demonstrating superior emulsifying capacity compared to phospholipids and forming the core of the interfacial layer [4]. The action of amphiphilic molecules integrating into the oil-water interface is a multistep and dynamic phenomenon encompassing diffusion, adsorption, conformational changes, and molecular reorientation. The competence of egg yolk proteins and lipids to interact with both oil and water phases stabilizes the emulsion by reducing interfacial energy and preventing droplet coalescence. The resulting protein-rich interfacial film functions as a protective barrier, hindering particle aggregation and enhancing overall emulsion stability [27; 28]. The performance of egg yolk proteins in food systems is directly linked to their structural makeup. Among the various factors influencing protein structure, pH and ionic strength are paramount. Subtle shifts in pH and ionic strength can significantly alter protein conformation, consequently impacting the overall characteristics and texture of emulsions [9]. [PERSON] and [PERSON] [29] investigated how pH and ionic strength affect the characteristics of egg yolk emulsions. They discovered that as pH and ionic strength increased, emulsion stability decreased until a critical point was reached at a pH of 6.08 and an ionic strength of 0.49 M NaCl. In contrast, [PERSON] et al. [30] found that the emulsion stability index increased with increasing pH (5 to 10), with an optimal NaCl concentration of 1.8% for maximum stability. The emulsifying activity of egg yolk dispersion improved with increasing pH from 5 to 7 but reduced as the pH was increased further to 10. Interestingly, NaCl concentration (0.3-3.0%) had no significant impact on emulsifying activity [30]. These contrasting findings maybe be due to differences in the protein concentration of the egg yolk used in these studies. For instance, the egg yolk in the [PERSON] and [PERSON] [29] study had a protein concentration of 0.25%, while in [PERSON] et al. 's [30] study, the concentration was 17.5% (raw yolk). A recent comprehensive study by [PERSON] et al. [9] provided new perspective on the impact of pH on egg yolk emulsifying properties. Egg yolk-based emulsions had the highest emulsifying activity at pH 5, while the highest emulsion stability was observed at both pH 3 and 9. Surprisingly, protein adsorption at the oil-water interface was more pronounced under acidic conditions (pH 3) than under alkaline conditions (pH 9). This discrepancy was credited to contrasting protein stabilization mechanisms at different pH levels. A thicker interfacial protein layer formed at pH 3.0, primarily stabilized by electrostatic repulsion. However, at pH 9.0, non-adsorbed proteins dispersed in the aqueous phase due to increased solubility and structural expansion, creating a steric barrier. Additionally, partial phospholipid (lecithin) substitution for interfacial proteins under alkaline conditions likely contributed to reduced protein adsorption (Figure 3). Notably, emulsifying activity did not consistently correlate with the emulsion stability. For instance, despite lower emulsifyingactivity at pH 3, superior emulsion stability was observed, potentially due to protein unfolding and enhanced solubility. The emulsion composition, including the interplay of egg yolk proteins and lecithin, significantly influenced emulsifying properties, highlighting the complex relationship between pH, protein behavior, and emulsifier composition in determining egg yolk emulsion characteristics. In terms of egg yolk components, egg yolk granules produced stable emulsions with excellent emulsifying stability at pH 4.