## 3 Factors Influencing and Mechanistic Pathways in Egg Yolk Emulsification
### Enzymatic Treatment  
Enzymatic hydrolysis is regarded as a safe and efficient method of improving the functional characteristics of proteins [83]. Proteases, including neutral protease, trypsin, and alkaline protease, are frequently employed to generate hydrolysate that enhance the emulsifying and solubility characteristics of proteins. Research has demonstrated that regulated enzymatic hydrolysis is an ideal approach for augmenting protein functionalities, since it can produce small soluble peptides and reveal more hydrophobic and ionizable protein residues. However, excessive enzymatic hydrolysis can negatively affect emulsifyingproperties. Moreover, the exact site of enzymatic action and the activity of the enzyme both affect the degree of hydrolysis. Hydrolysates with the same degree of hydrolysis, produced by different enzymes, can exhibit varying physicochemical properties [84; 85]. Thus, this section will explore recent advances in the use of enzymes to improve egg yolk and its components' emulsifying properties. [PERSON] et al. [41] showed that hydrolysis times during dual enzymatic hydrolysis using neutrale (0.1% \(w/w\)) and trypsin (0.15% \(w/w\)) affected the egg yolk emulsifying properties. The degree of hydrolysis increased with longer hydrolysis times, reaching 4.4% at 4.5 h. However, the optimal hydrolysis times for emulsifying activity were between 1.5 and 3.5 h. Shorter (0.5 h) or longer (4.5 h) hydrolysis times led to reduced emulsifying activity. All hydrolyzed egg yolk samples exhibited higher emulsifying capacity than the untreated egg yolk, with the highest value at 1.5 h of hydrolysis [41]. The ability of a protein to function as an emulsifier is correlated with its surface hydrophobicity, where a higher hydrophobicity produces better emulsifying properties. While smaller peptides with both hydrophobic and hydrophilic functional groups can migrate to the oil-water interface and stabilize the emulsion by lowering the interfacial tension, larger polypeptide chains can produce a stronger interfacial film around oil droplets [86; 87]. Additionally, emulsions made with the dual enzymatic hydrolyzed egg yolk exhibited enhanced thermostability [41]. Similarly, alkaline protease modified egg yolk produced thermally stable emulsions along with improved emulsifying properties [42]. Hydrolyzed egg yolk proteins had lower molecular weights and exhibited increased protein solubility compared to non-hydrolyzed proteins. Additionally, hydrolysis altered the ionization of amino acids, increasing their net charge. Improved heat stability was achieved by the modified egg yolk emulsions as a result of the combination of lower molecular weight and increased electrostatic charge delaying the gelation point [41; 42]. Fermentation with lactic acid bacteria is a safe and natural method to modify food proteins. Egg yolk emulsifying qualities were improved, depending on the length of fermentation, when commercial lactic acid bacteria were used. The emulsifying activity increased with longer fermentation times (3, 6, and 9 h); however, egg yolk fermented for 3 h showed the maximum emulsifying stability, with no significant changes observed after 6 and 9 h of fermentation compared to unfermented samples [88]. Another study by the same group found that lactic acid bacteria fermentation of phosvitin enhanced its emulsifying activity and stability with fermentation times of 3 and 6 h, but these properties decreased when the fermentation time was extended to 9 h. Additionally, the calcium-binding capacity of phosvitin phosphopeptides produced from fermentation-treated phosvitin was greater than that of native phosvitin. Fermented phosvitin phosphopeptides exhibited higher calcium-binding capacity, indicating their potential for therapeutic or health-promoting applications [43]. Furthermore, [PERSON] and [PERSON], [44] found that phospholipase A\({}_{2}\)-treated egg yolk had enhanced emulsifying properties compared with untreated egg yolk.