## 3 Results and Discussion
### Effect of HPP on the Free Amino Acids Profile of Beef During Storage
[PERSON] et al. [4] also found that the release of amino acids during the storage of ground beef was partially altered after the HPP treatment, but it depended on the applied pressure. Analyzing the cited studies [4; 42], similar patterns of increases in amino acids were observed to those observed in our studies. However, the absolute values differed significantly. The contents of free amino acids in beef reported in the literature are very diverse, as they are highly dependent on the type of the muscle, meat treatment, and storage time and conditions. [PERSON] et al. [45] observed that pressures of 300 to 400 MPa (10 min at 20 \({}^{\circ}\)C) could stabilize the free amino acid content during the storage of dry-cured loin due to the decreased activity of aminopeptides. Thistrend was also visible in our studies, as the threonine content in the HPP500 meat increased more slowly during storage. Beef was characterized by a methionine content of 28.87-33.09 mg/kg on 1 st day of storage, and at the end of the storage time, it ranged from 91.44 to 193.46 mg/kg (Table 2). The methionine content in beef on 1 st day of storage was not significantly (\(p>0.05\)) differentiated by the applied high pressure. From the 7 th day of storage, it was observed that exposure to higher pressures resulted in greater losses of this amino acid content compared to the control meat. Starting from the 21 st day of storage, the HPP500 meat was characterized by the significantly lowest methionine content and was even 2-fold lower than for the control. Moreover, from the 28 th day of storage, significant differences were observed in the methionine content of the beef treated by HPP. On the last day of storage, the methionine content was 196.43 mg/kg for the control meat and 91.44 mg/kg for the HPP500 meat. The influence of HPP on the methionine content was also observed by [PERSON] et al. [4]. Similarly to threonine, an increase in the methionine content was also observed during storage. An increase (\(p\leq 0.05\)) compared to day 1 was observed from day 14 of storage, regardless of the treatment. Moreover, the dynamics of this increase were different for the control and HPP300 meat, and for the HPP400 and HPP500 meat. For the control and HPP300 meat, on the last day of storage, the methionine content was approximately 6-fold higher compared to day 1 (33.09 vs. 193.46 and 31.53 vs. 176.5 mg/kg, respectively), and for the HPP400 and HPP500 meat, it was approximately 3-4-fold higher (31.87 vs. 117.45 and 28.87 vs. 91.44 mg/kg, respectively). [PERSON] et al. [4] and [PERSON] et al. [42] demonstrated a specific release of methionine content during storage. [PERSON] et al. [46] found that the methionine, tyrosine, and leucine content increased even 7-15-fold times during beef storage. The valine content in beef on 1 st day of storage ranged from 42.41 to 48.83 mg/kg and on the last day of storage, it was from 134.62 to 358.62 mg/kg. It was observed that exposure to HPP resulted in greater losses in the content of this amino acid compared to the control meat. On the 1 st day of storage, the HPP500 meat already had a significantly lower valine content than the control meat, and this trend continued until the end of the storage (on day 56, it was approximately 3-fold lower; 134.62 vs. 358.62 mg/kg, respectively). From day 7, the HPP400 meat also had a significantly lower valine content than the control meat, and on day 56 of storage, significant differences in the valine content were found between all treatments. The valine content of beef increased (\(p\leq 0.05\)) during storage. The increase compared to day 1 was observed from day 14 of storage, regardless of the treatment. The dynamics were the highest for the control meat (approximately 8-fold higher during 56 days of storage, up to 358.62 mg/kg) and lower when higher pressures were applied (for HPP300, HPP400, and HPP500 meat, it was approximately 7, 4, and 3-fold higher, up to 317.58, 196.23, and 134.62 mg/kg, respectively). In the study by [PERSON] et al.