## 3 Factors Influencing and Mechanistic Pathways in Egg Yolk Emulsification
### Chemical Treatment
#### 3.1.1 pH and Ionic Strength
Above pH 4, poor emulsion stability was detected with oil separation. Conversely, at pH below 4, particle size distribution was uniform and narrow, with a particularly uniform particle size of ~50 \(\upmu\)m at pH 4. Particle size continuously grew to over 200 \(\upmu\)m at pH values above the isoelectric point (pl) of 4. Notably, egg yolk granules were unable to stabilize emulsion with particle size < 10 \(\upmu\)m [31]. Along with pH, the type of oil significantly impacts interfacial tension. Regardless of oil type, increasing pH correlated with a decrease in interfacial tension. The initial decrease from pH 3 to 4 was gradual, but the reduction became more pronounced at higher pH levels, especially in the alkaline range (pH 8 and 10). Rapeseed oil exhibited the highest interfacial tension against both 0.15 M NaCl solution and 2% granule solution. Sunflower and peanut oils showed intermediate values, while corn oil consistently displayed the lowest interfacial tension across all pH conditions [32]. Furthermore, [PERSON] et al. [33] unveiled the Janus effects of NaCl on granule structure across varying pH conditions. In the absence of NaCl, granule self-assembly was primarily influenced by the interplay of attractive calcium bridges and repulsive electrostatic forces. Dispersions formed using granules were stable at pH values outside the range of 4 to 7, but phase separation took place within that pH range. Introducing 0.3 and 0.5 M NaCl disrupted calcium bridges, leading to granule dissociation between pH 4 and 7, with a more pronounced effect at pH 6 and 7. At pH 2 and 3, the same NaCl concentration induced reaggregation of dissociated granules. However, NaCl had a negligible impact on granule aggregation at pH 5 to 10. This dual behavior was attributed to counter ion adsorption on the granule surface. Above pH 5, negatively charged granules adsorbed highly hydrated Ca\({}^{2+}\) and Na\({}^{+}\) ions, resulting in strong hydration repulsion and stable dispersions. Conversely, at pH levels below 4, Cl' ion adsorption led to insufficient hydration repulsion and subsequent phase separation (Figure 4). Figure 3: Schematic mechanism of protein and phospholipid adsorption at the oil–water interface under different pH conditions. Reprinted with permission from [PERSON] et al. [9]. 2023, Elsevier. A study by [PERSON] et al. [34] used calcium chelators to enhance the interfacial activity and water dispersity of granules. The addition of sodium tripolyphosphate (Na\({}_{5}\)O\({}_{10}\)P\({}_{3}\)), trisodium citrate (C\({}_{6}\)H\({}_{5}\)Na\({}_{3}\)O\({}_{7}\)), and ethylenediaminetetraacetic acid disodium (EDTA-2 Na) at a concentration of 0.15 weight% (wt.%) dissociated granules into nanoparticles from micro-sized, which exhibited improved colloidal stability at pH 7. The dissociation effect was diminished or absent at pH 3 and 5.5. Chelators disrupted the granule by chelating and disrupting Ca\({}^{2+}\) bridges as confirmed by an analysis of unbound calcium ions. Emulsions formulated with these dissociated granules demonstrated reduced particle size and improved stability. Phosvitin, a key component of hen egg yolk, exhibits a strong affinity for multivalent cations and possesses emulsifying properties. While non-aggregated phosvitin excels in emulsifying activity, aggregated phosvitin demonstrates superior emulsion stability against coalescence. Lower ionic strength (0.05 M) favored the creation of finer emulsions compared to higher (0.15 M). The concentration of NaCl had a significant effect on flocculation, with the highest level of flocculation occurring when aggregated phosvitin was combined with an ionic strength of 0.15 M. Hydrophobic interactions contributed to the stability of phosvitin aggregates. The findings suggest that controlling the initial conditions of the protein solution can effectively modulate the various mechanisms underlying phosvitin emulsion destabilization [35].