## 3 Results and Discussion
### Surface Hydrophobicity  
The surface hydrophobicity of the whey protein with and without modification with oxidized phenolic compounds is shown in Table 1. Changes in the surface hydrophobicity of the modified whey protein occurred when compared with the control. This was possibly due to the difference of change in the structure and functional groups of the whey protein after modification. Interaction between the oxidized phenolic compounds and whey protein could change the protein conformation and the exposure of hydrophobic groups, resulting in a change in surface hydrophobicity of the whey protein [20]. The whey protein modified with OTA and OGA had decreased surface hydrophobicity with increasing concentrations of compounds used (\(p<0.05\)). [PERSON] et al. [21] reported that the surface hydrophobicity of soy protein decreased when reacted with phenolic compounds. [PERSON] et al. [22] reported that the covalent attachment of the phenolic compound to proteins caused the blocking of hydrophilic groups such as amino and thiol groups. Incorporation of gallic acid and tannic acid with high hydroxyl and carboxyl group content into the whey protein led to an increase in hydrophilicity of the modified whey protein. When the increase rate of the hydrophilic group was higher than that of hydrophobic group, the whey protein modified with OTA and OGA showed a decrease in surface hydrophobicity.  
However, the whey protein modified with OFA showed different results. The modification of the whey protein with OFA led to a change in surface hydrophobicity, depending on the OFA concentration used. The whey protein modified with 0.5-2.5% OFA had higher surface hydrophobicity than the control, whereas the whey protein modified with 5% OFA had similar surface hydrophobicity to the control. This might be associated with the degree of increase in the hydrophilic group on the whey protein attached with ferulic acid compared with the loss in the hydrophilic group (such as amino or thiol groups) of the whey protein during interaction. At an OFA concentration of 0.5-2.5%, the loss in the hydrophilic group of the whey protein from interaction with OFA was probably higher than the increase in the hydrophilic group on the whey protein attached with ferulic acid, leading to an increase in surface hydrophobicity. However, as the concentration of OFA was increased to 5%, the increase in the hydrophilic group on the whey protein attached with ferulic acid on the surface was probably higher than the loss in the hydrophilic group of the whey protein from interaction, resulting in a decrease in surface hydrophobicity of the resulting whey protein.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Concentrations of**} & \multicolumn{3}{c}{**ANS (S\({}_{0}\))**} \\ \cline{2-4}
**Oxidized Phenolic Compounds** & **WP-OGA** & **WP-OFA** & **WP-OTA** \\ \hline
0 (control) & 1172.5 & 1172.5 & 1172.5 \\
0.5 & 905.8 & 1722.5 & 845.0 \\
0.1 & 897.5 & 1730.0 & 632.5 \\
2.5 & 540.0 & 1742.5 & 578.3 \\
5 & 315.0 & 1197.5 & 110.1 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Surface hydrophobicity of whey protein modified with different oxidized phenolic compounds at various concentrations.