## 4 Discussion
### pH Behavior and the Amino Acid Profile of Egg Samples  
The composition of free amino acids in Figure 1 for sample W shows a higher composition of hydrophilic amino acids, L-aspartic acid 11.7 \(\pm\) 0.10, L-arginine 3.94 \(\pm\) 0.01 and L-glutamic acid and glutamine 3.70 \(\pm\) 0.30, followed by hydrophobic amino acids, such as L-phenylalanine 3.25 \(\pm\) 0.00 and L-tryptophan 1.75 \(\pm\) 0.01. In the analysis of the total amino acids, the amino acid trans-4-hydroxy-L-proline was found only in sample W at a concentration of 2.56 mg/100 g (dry basis) (see Figure 2). The presence of L-arginine as a free amino acid is one of the causes of the change in pH experienced by sample W after drying, which went from a pH of 8.06 for the liquid sample to 9.78 for the dried powder. During the drying process, the L-arginine side chain, guanidine, may be exposed to heat denaturation, which causes an increase in pH due to the alkaline nature of this substance. Likewise, the exposure of groups of the side chain of other basic amino acids increases the pH of egg powders [8]. The increase in the pH of dried egg products has also been attributed to the evaporation of dissolved CO\({}_{2}\). The release of this gas produces changes in the balance of the carbonate-bicarbonate buffer present in the egg. The system tries to compensate for the loss of gas by moving the balance to the carbonate side, causing an increase in pH [8,43]. According to the results of the total amino acid composition of the egg powders (see Figure 2), the predominant amino acids for sample W were: L-valine 3638 \(\pm\) 1053; L-leucine 2917 \(\pm\) 741, and L-alanine 1265 \(\pm\) 35, which are hydrophobic because they present nonpolar groups in their side chain, such as isopropyl, isobutyl, and methyl, respectively [44].This could be one of the causes of the lower solubility of W compared to that in WE5% and M1:3 since the solubility of proteins in water is influenced by the pH and the functional group present in the side chain of its structure [45]. The hydrophobicity of these amino acids could be one of the causes of the long wettability times found for sample W of 4.700 s at 25 \({}^{\circ}\)C and 7.478 s at 50 \({}^{\circ}\)C. The denaturation of proteins during the spray-drying process of the egg white causes conformational changes that lead to the exposure of hydrophobic groups on its surface, thus reducing the wetting capacity of the product [46]. The addition of sucrose to the treatments with 5% and 7.5% for sample W prevented the pH from exceeding a value of 10, as established in NTC 6116 [16]. This could be explained by the protective nature of carbohydrates, which prevent the denaturation of proteins and, consequently, the exposure of the side chains of basic amino acids, such as L-arginine, L-leucine, and L-histidine [7,13]. In the WE5% sample, the predominant amino acids were L-aspartic acid and L-glutamic acid. These have carboxyl groups in their side-chain that completely ionize at neutral pH, favoring their solubilization in water [47]. This could account for the fact that the pH of the WE5% powder was lower compared to that of the W and M1:3 samples (see Table 2), which presented a lower proportion of these two amino acids. The pH of all rehydrated egg powders was far from the corresponding isoelectric point (IP) reported for the predominant amino acids in each sample: L-aspartic acid for WE5%, with a PI of 2.77; L-glutamic acid for M1:3, with a PI of 3.22 and L-valine for W, with a PI of 5.96, which could have promoted their solubility in water [47]. The contents of free amino acids in fresh eggs are influenced by chicken breeds and feed compositions. Likewise, the amount and distribution of free amino acids in egg powders influence the sensory and functional properties of food products [48]. [PERSON], et al. [48]reported that amino acids are precursors of different flavors by interacting with other components in food matrices.