## 3 Results and Discussion
### FTIR Analysis
HIGs: conventional heat-induced gels; PG300/1%: salt concentration 1% and 300 MPa/10 \({}^{\circ}\)C/10 min; PG300/2%: salt concentration 1% and 300 MPa/10 \({}^{\circ}\)C/10 min; PG400/1%: salt concenration 1% and 400 MPa/10 \({}^{\circ}\)C/10 min; PG400/2%: salt concentration 1% and 400 MPa/10 \({}^{\circ}\)C/10 min; PG500/1%: salt concentration 1% and 500 MPa/10 \({}^{\circ}\)C/10 min; PG500/2%: salt concenration 1% and 500 MPa/10 \({}^{\circ}\)C/10 min; PG500/2%: salt concenration 1% and 500 MPa/10 \({}^{\circ}\)C/10 min. 1604 \(\pm\) 0.58 cm\({}^{-1}\) could be aromatic side chain vibrations of amino acids such as tyrosine, phenylalanine, or tryptophan [44; 45; 46]. The results in Table 3 show the percentage of the secondary structure of the pangasius protein treated at different HPP conditions and HIGs. The \(\alpha\)-helix content was significantly higher in the HPP samples compared to the HIG control (\(p<0.05\)). The stabilization of \(\alpha\)-helix under high-pressure conditions can be attributed to the ability of HPP to maintain intramolecular hydrogen bonds, preventing thermal denaturation. [PERSON] et al. [41] showed that high pressure also increased \(\alpha\)-helix content in flying fish surimi that was pressurized and then cooked. Moreover, [PERSON] et al. [47] suggested that high pressure helps preserve \(\alpha\)-helix structures in proteins by restricting the unfolding process and minimizing heat-induced transitions to \(\beta\)-sheet or random coil structures. In contrast, [PERSON] et al. [5] reported that the \(\alpha\)-helix structure of isolated hake myofibrils remained similar between heated samples (90 \({}^{\circ}\)C for 20 min) and those subjected to pressure treatment (150-250 MPa at 10 \({}^{\circ}\)C for 10 min) followed by heating (90 \({}^{\circ}\)C for 20 min). Unlike \(\alpha\)-helix structures, \(\beta\)-sheet and \(\beta\)-turn contents showed no significant differences among all treatments, including HIGs. The \(\beta\)-sheet content remained relatively stable, ranging from 29.22% to 31.18%, while \(\beta\)-turn content fluctuated minimally between 19.64% and 20.14%. This suggests that these structures are stable under the thermal and high-pressure conditions. These findings align with previous reports suggesting that \(\beta\)-sheets are stabilized by strong inter-chain hydrogen bonds, which are resistant to both thermal and pressure-induced conformational changes [48; 49]. Figure 6: Second-derivative of Amide I band (1700–1600 cm\({}^{-1}\)) of infrared spectra of pangasius gels added 1 and 2% salt under different HPP treatments over the frequency range 1700–1600 cm\({}^{-1}\). Peaks corresponding to \(\alpha\)-helix (\(\sim\)1654 cm\({}^{-1}\)), \(\beta\)-sheet (\(\sim\)1625, \(\sim\)1696 cm\({}^{-1}\)), \(\beta\)-turn (\(\sim\)1680 cm\({}^{-1}\)), and random coil (\(\sim\)1648 cm\({}^{-1}\)) indicate structural changes in the protein secondary structure of different treatments. HIGs: conventional heat-induced gels; PG300/1%: salt concentration 1% and 300 MPa/ 10 \({}^{\circ}\)C/10 min; PG300/2%: salt concentration 1% and 300 MPa/10 \({}^{\circ}\)C/10 min; PG400/1%: salt concentration 1% and 400 MPa/10 \({}^{\circ}\)C/10 min; PG400/2%: salt concentration 1% and 400 MPa/10 \({}^{\circ}\)C/10 min; PG500/1%: salt concentration 1% and 500 MPa/10 \({}^{\circ}\)C/10 min; PG500/2%: salt concen-tration 1% and 500 MPa/10 \({}^{\circ}\)C/10 min. At a 2% salt concentration, the random structure content was similar between pressure-induced gels and HIGs. However, random structure content was significantly lower in high-pressure-treated samples compared to the HIG control (_p_ < 0.05) at reduced salt concentration (1%). This suggests that the less random structure of pressure-induced gels with 1% added salt was denatured compared to HIGs with 2% salt. Thus, HPP can result in molecular reorganization and influence the degree of protein denaturation in different patterns at different salt concentrations.