## 3 Results and Discussion
### Effect of HP on the Physicochemical Characteristics of Sea Bass Fillets
In contrast to untreated sea bass fillets for which the hardness values exhibited a significant (\(p<0.001\)), almost 4-fold, increase during storage (statistical mean value of hardness: 140 and 410 g at day 0 and 15, respectively), the hardness of the HP-treated sea bass fillets did not significantly change during storage, regardless of the applied pressure, processing temperature and time, and the storage conditions, which is in agreement with previous studies [12; 27]. Regarding adhesiveness, both untreated fillets and sea bass fillets pressurized at a pressure of 100 MPa showed the highest values, while the lowest values were obtained for samples pressurized at 400 MPa, regardless of any other processing or storage parameter. Overall, it was observed that as the applied pressure increases, the value of adhesiveness decreases, which is also related to the increase in hardness values and the loss of stickiness of the fish fillets. An increase in the processing temperature led to a significant decrease in the adhesiveness, mainly for fish fillets treated at pressures above 300 MPa combined with temperatures above 3 \({}^{\circ}\)C (statistical mean value of adhesiveness: 22.0, 27.1, 6.6, and 6.1 g s for sea bass fillets treated at 100, 200, 300, and 400 MPa, respectively, and, statistical  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Fish Filled Treatment** & **pH Value** & **Hardness (g)** & **Adhesiveness (g s)** \\ \hline Untreated fillet & 6.53 \({}^{\circ}\)(\(\pm\)0.02) & 127 \({}^{\text{a}}\) (\(\pm\)9.94) & 20.2 \({}^{\text{e}}\) (\(\pm\)4.67) \\ \hline Untreated fillet (aerobically stored) & 6.70 \({}^{\text{de}}\) (\(\pm\)0.12) & 151 \({}^{\text{a}}\) (\(\pm\)17.9) & 9.91 \({}^{\text{cd}}\) (\(\pm\)1.31) \\ \hline  
}}\) (\(\pm\)0.04) & 282 \({}^{\text{bc}}\) (\(\pm\)32.7) & 20.6 \({}^{\text{e}}\) (\(\pm\)mean value of adhesiveness: 21.6 and 14.7 g-s for sea bass fillets treated at 3 and 25 \({}^{\circ}\)C, respectively). Finally, processing time did not affect the adhesiveness parameter, at least in the low temperature range studied (3 \({}^{\circ}\)C) where it was the case that the highest value of adhesiveness, higher than that of the untreated fillets, was observed for the fillets that were pressurized at 200 MPa. Similar to the hardness results, the adhesiveness of the HP-treated fish fillets did not exhibit any significant change during storage. However, the adhesiveness of the untreated fillets exhibited a 2-fold increase during storage (statistical mean value of adhesiveness: 15.5 and 33.0 g-s at day 0 and 15, respectively); this is probably related to the gradual softening of the fish muscle during storage under chilled conditions. As it is related to the freshness of the product, color is considered a fundamental attribute of raw fish and plays a significant role in consumer acceptance [49; 50]. The initial color parameter of the lightness (\(L^{\star}\)) of fish samples was 43.6 \(\pm\) 2.19, 53.7 \(\pm\) 1.43, 68.0 \(\pm\) 2.37, 82.2 \(\pm\) 5.22, and 87.1 \(\pm\) 3.70 for untreated or HP-treated fillets at 100, 200, 300, and 400 MPa, respectively, indicating the significant (\(p\) < 0.01) whitening effect of HP processing on fish flesh, especially at pressures above 100-150 MPa (Figure 3b). These results are in agreement with previous results obtained in gilthead seabream fillets [27] and the results of other research on salmon and plaice fillets [49], cod (_Gadus morhua_) fillets [12], haddock and mackerel [51; 56], hilsa shad (_Tenualosa ilisha_) fillets [55], and milkfish (_Chanos chanos_) fillets [45]. This phenomenon is related to the denaturation of the proteins of the fish muscles, leading to an increase in the light reflection.