## 3 Results and Discussion
### Estimation of Microbial Growth Parameters and Shelf Life
#### 3.2.2 Microbial Growth Curves of HPP Samples
High-pressure treatment may have caused sublethal damage for some of the LAB at the beginning of storage. The bacteria could recover and outgrow during the late period of storage at all storage temperatures examined. The results of the analyses conducted confirm the positive effect of high-pressure processing (HPP) on slowing down microbial growth in the studied sausages, and consequently on their shelf life. Overall, these results indicate the effectiveness of the combined effect of HPP and low storage temperatures in enhancing the quality and shelf life of processed meat products. For instance, the shelf life of the HPP sausages was extended by approximately 70 days compared to the CNT samples during their storage at 4 \({}^{\circ}\)C. This significant extension in shelf life was observed in the HPP-treated samples compared to the corresponding samples that had not undergone HPP (CNT). Previous studies conducted on cooked ready-to-eat meat products indicated that HPP can significantly extend the shelf life of vacuum-packed meat products such as wieners, turkey breast ham, cooked pork ham, dry-cured ham and marinated beef loin [9; 39; 59; 60; 61; 62]. HPP is known to effectively inactivate a wide range of microorganisms, including spoilage bacteria and pathogens, by  
Figure 8: Growth of total viable count in frankfurter-type sausages after HPP (HPP samples) during storage at **(a)** 4, **(b)** 8, **(c)** 12, and **(d)** 18 \({}^{\circ}\)C. Data points are means of four replicates, and error bars represent the corresponding standard deviation values. Solid lines represent the application of the [PERSON] and Roberts microbial growth model as described in Equation (1). applying high pressure (typically between 400 and 600 MPa) for a few minutes at room temperature [63]. This process disrupts the cellular functions of microorganisms, leading to their inactivation without significantly affecting the sensory and nutritional qualities of the food. Studies have shown that HPP can significantly reduce the populations of spoilage microorganisms such as _Pseudomonas_ spp., _Lactobacillus_ spp., and _Enterobacteriaceae_ spp., thereby enhancing the safety and extending the shelf life of meat products. For example, research has demonstrated that combining HPP with natural antimicrobials like spice extracts can further inhibit microbial growth and improve the storage quality of low-salt sausages [40]. Moreover, the application of HPP has been found to delay the onset of spoilage by extending the lag phase and reducing the growth rate of microorganisms during storage [63]. This is particularly beneficial for products stored under refrigeration, as it helps products maintain their quality and safety over extended periods. In conclusion, the use of HPP in the processing of frankfurter-type sausages has been validated as an effective method to prolong shelf life and ensure microbial safety, making it a valuable processing tool in the food industry. To determine the kinetic parameters of TVC growth, the Baranyi and Roberts [30] model was applied, and the data for TVC growth in the HPP-treated frankfurter-type sausages are presented in Table 2.  
Figure 9: Growth of lactic acid bacteria in frankfurter-type sausages after HPP (HPP samples) during storage at **(a)** 4, (b) 8, (c) 12, and (d) 18 \({}^{\circ}\)C. Data points are means of four replicates, and error bars represent the corresponding standard deviation values. Solid lines represent the application of the Baranyi and Roberts microbial growth model, as described in Equation (1).