## 3 Results and Discussion
### Effect of HPH on Protein Functional Properties  
The water- and oil-holding capacities of APPCs from untreated and HPH-treated biomass are shown in Figure 4. Treatment at 600 bar for one pass led to a significant increase in oil-holding capacity (OHC) of 11.0% compared to untreated samples. The increase in OHC is attributed to the effect of HPH on protein structure (Table 1), where higher treatment pressure exposes the hydrophobic protein core, enhancing this functional property. The exposure of the hydrophobic protein core reveals lipophilic groups that can form intermolecular bonds with lipids, thereby increasing the oil-holding capacity. As these lipophilic groups become exposed, the hydrophilic groups are reduced, resulting in an inverse trend in water-holding capacity (WHC) compared to OHC. The increase in the number of passes from 1 to 4 led to lower values of OHC and WHC, which may be attributed to the lower APPC protein content in these samples (Figure 1). [PERSON] et al. (2018) had also reported a significant increase in OHC and a significant reduction in _WHC_ by applying a one-pass HPH treatment at 600 bar (60 MPa) at oyster protein isolates [PERSON] et al. (2018). The dependence of surface tension of APPC aqueous solutions on the solution protein concentration for each HPH treatment is presented in Figure 3. One very important criterion for the estimation of the emulsifying potential of an emulsifier candidate is the satisfactory reduction of the surface tension of its aqueous solution [PERSON] et al. (2018). As observed in Figure 3, increasing the protein concentration resulted in surface tension reaching a plateau value between 28.6 mN/m and 35.6 mN/m. For all the HPH treatment conditions, the surface tension was practically stabilized with a deviation of less than 5% from the plateau at protein concentrations between 1.02% \(w/w\) and 1.19% \(w/w\), corresponding to an APPC concentration of 2% \(w/w\). For comparison reasons, the surface tensions of 2% \(w/w\) Tween 20 and sodium caseinate solutions were measured, yielding values of 33.1 mN/m and 44.5 mN/m, respectively. Tween 20 and sodium caseinate are commonly \begin{table}
\begin{tabular}{c c c c c} \hline  & \(\alpha\)-Helix (\%) & \(\beta\)-Sheet (\%) & \(\beta\)-Turn (\%) & Random Coil (\%) \\ \hline Control & 14.28 \(\pm\) 0.05 a & 25.71 \(\pm\) 0.08 a & 37.08 \(\pm\) 0.03 a & 22.93 \(\pm\) 0.05 a \\
400 bar & 14.25 \(\pm\) 0.04 a & 25.58 \(\pm\) 0.08 a & 37.20 \(\pm\) 0.03 a & 22.97 \(\pm\) 0.05 a \\
600 bar & 13.57 \(\pm\) 0.01 b & 24.80 \(\pm\) 0.08 b & 38.03 \(\pm\) 0.03 b & 23.60 \(\pm\) 0.05 b \\
800 bar & 12.74 \(\pm\) 0.02 c & 23.58 \(\pm\) 0.06 c & 39.64 \(\pm\) 0.02 c & 24.04 \(\pm\) 0.05 c \\ \hline \end{tabular} Different superscript letters within a column represent significant differences as calculated by [PERSON]’s multiple range test for a significance level of \(p<\) 0.05.  
\end{table} 
Table 1: Secondary structure of untreated (control) and HPH-treated APPC from untreated _A. pytorch3_ biomass. Figure 2: FTIR spectra of untreated (control) and high-pressure homogenization (HPH) treated _A. pytorch3_protein concentrate (APPC). Label values indicate the peaks of FTIR spectra. used as emulsifiers in food and cosmetic industries, renowned for their excellent surface activity [6; 41]. However, with the industry's shift towards more natural, plant-based emulsifiers like APPCs, there is a growing demand for cleaner and more sustainable ingredients to meet consumer preferences. Comparing these results, it is clear that the APPCs reduce the surface tension to satisfactory levels. Based on these results, the APPC concentration of 2% \(w/w\) was chosen as the optimum emulsifier concentration for the emulsion preparation. Another significant criterion for evaluating the emulsifying potential of an emulsifier candidate is the interfacial tension. Specifically, interfacial tension values between 1 mN/m and 10 mN/m indicate an optimal balance between the viscous drag force and the interfacial tension force acting on a droplet [42].