## 4 Conclusions  
The results indicate that the high-pressure treatment, particularly at 500 MPa, slowed the reduction in the pH level, but concurrently accelerated the lipid oxidation process and affected the color parameters of beef during storage. It should be noted that any changes in the above-mentioned quality parameters could negatively affect the sensory attributes of beef. To optimize the long-term storage of culinary beef treated with HPP, a sensory evaluation should be included in the research scope, which was the limitation of our study.  
For most of the free amino acids analyzed, HPP reduced their content compared to the control beef, with greater losses observed at higher pressure levels. However, over the storage period, the free amino acid contents generally increased, with the exception of lysine. The dynamics of this increase were usually higher for the control and HPP300 meat and lower for the HPP400 and HPP500 meat. This difference could likely be attributed to variations in the microbiological activity among the tested meat samples, especially during prolonged storage. Based on these findings, to minimize undesirable changes in the quality of culinary beef, it is advisable to use lower pressure levels, specifically in the range of 300-400 MPa. However, it is important to note that such lower pressures may have a smaller effect on the microbiological stability of the HPP-processed meat.  
The findings of this study can be utilized to enhance methods for extending the shelf-life of culinary beef using high-pressure processing and refrigerated storage. Gaining a better understanding of the changes that occur in beef, including monitoring the levels of free amino acids--many of which serve as precursors to biogenic amines--can help improve the health safety of the meat. However, our study has further limitations, including the lack of research data on changes in beef quality that occur shortly after HPP treatment. Research in this area seems essential, particularly due to the high operating costs associated with using high-pressure processing to extend the shelf-life of culinary beef.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app15052382/s1](https://www.mdpi.com/article/10.3390/app15052382/s1)]([https://www.mdpi.com/article/10.3390/app15052382/s1](https://www.mdpi.com/article/10.3390/app15052382/s1)), Figure S1: Representative LC-MS/MS chromatograms showing peaks of analyzed free amino acids in (A) analytical standards solution at concentration 1000 ng/mL and (B) example of beef sample.  
Figure 4: Correlation circle for principal components.  
**Author Contributions:** Conceptualization, M.C., A.C. and M.R.; methodology, O.S.; formal analysis, L.A.; investigation, M.C., O.S., M.R., A.C., D.P., T.F. and M.B.; writing--original draft preparation, M.C., O.S., L.A., A.C. and A.F.; writing--review and editing, M.C. and A.F. All authors have read and agreed to the published version of the manuscript.  
**Funding:** The research for this publication was carried out using research equipment purchased as part of the \"Food and Nutrition Centre-moderation of the WULS campus to create a Food and Nutrition Research and Development Centre (CZiZ)\" co-financed by the European Union from the European Regional Development Fund under the Regional Operational Programme of the Mazowieckie Voivodeship for 2014-2020 (Project No. RPMA.01.01.00-14-8276/17).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding authors.  
**Conflicts of Interest:** The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.