## 3 Results and Discussion  
### Physicochemical Analysis  
In Figure 1a,b, the pH values of the reference samples (CNT) and the HPP-treated samples are depicted during their storage at 4, 8, 12, and 18 \({}^{\circ}\)C, respectively. The pH value is an important parameter in monitoring meat quality. The pH values of the samples under various isothermal storage conditions (4, 8, 12, and 18 \({}^{\circ}\)C) ranged from 6.3 (day 0) to 4.8 for the CNT samples and 5.3 for the HPP samples at the end of the storage time. Over the storage time, the pH of the frankfurters decreased significantly (\(p<0.05\)) in all treatments. This significant decrease in pH began on day 20 for the CNT samples and on day 96 for the HPP samples stored at 4 \({}^{\circ}\)C. The pH values of all samples gradually decreased with increasing storage time. In general, when the main spoilage microorganism LAB reached high levels (6.5-8 log CFU/g) in all frankfurter sausages, the pH began to decrease (\(p<0.05\)), which may be attributed to the organic acid accumulation produced by spoilage microorganisms [35; 36]. LAB are known to produce organic acids such as lactic acid, acetic acid, and formic acid, which contribute to a decrease in the pH values of meat products. The extent of acid production depends on factors such as genus, species, and the specific growth conditions [37]. The reduction in pH within meat products is also largely influenced by the availability of fermentable carbohydrates. For instance, [PERSON] et al. [38] observed a decline in the pH of turkey fillets during storage, from an initial value of 6.2 to 5.5. However, in piroshki sausages, which contain lower levels of carbohydrates, the rate of pH decrease was slower compared to turkey fillets. Similarly, [PERSON] et al. [39] reported a significant decrease in the pH of vacuum-packed, untreated, and HPP-treated cooked ham at 400 or 500 MPa over the course of storage. The results of the present study also agree with the results of [PERSON] et al. [40]. Considering that all samples showed a decrease in pH value and increase in the growth of lactic acid bacteria, yet the same drop in pH value was not observed, it can be concluded that at higher storage temperatures, additional chemical and biochemical phenomena are likely to occur and accelerate, affecting the pH value of the overall system. These reactions seemed to slow down in the case of HPP samples, as in this case, the decrease in pH value was lower. The samples stored under dynamic conditions with T\({}_{\text{eff}}\) = 4.5 \({}^{\circ}\)C exhibited similar behavior to those stored under isothermal conditions of 4 \({}^{\circ}\)C, with the HPP samples showing an overall slight, yet significant (\(p<0.05\)), pH drop of approximately 0.3 units (from an initial mean value of 6.31 \(\pm\) 0.01 to a final mean value of 6.19 \(\pm\) 0.04). Figure 1: Mean pH values (\(\pm\)standard deviation) of (**a**) CNT and (**b**) HPP frankfurter-type sausages during storage under isothermal temperature conditions. Figure 2a,b show the evolution of the color parameters L*, a, and b of the reference samples (CNT) and the HPP-treated samples during their storage at 4, 8, 12, and 18 \({}^{\circ}\)C and dynamic storage conditions (VAR1, VAR2). The results obtained indicate that neither the application of HPP on the meat products nor the storage time affected the values of the tested color parameters. These findings are in accordance with previous studies where the application of pressures up to 600 MPa for 5 min did not lead to color changes during the storage of either sliced cooked ham and turkey or bratwurst sausages [9]. Regarding the cutting force and the textural attributes of the studied frankfurter-type sausages, the results show that the application of HPP did not significantly (\(p>0.05\)) affect either the cutting force or the hardness, index of elasticity, adhesiveness, gumminess, and chewiness of the samples.