## 4 Discussion
However, the water activity of experimental sausages, regardless of the additive used in the production process, was lower than the minimum necessary for the development of most pathogenic microorganisms, such as: _Pseudomonas_ (aw > 0.97), _Clostridium botulinum_ (aw > 0.93 \(\div\) 0.96), _Salmonella_ (aw > 0.94) and _Listeria monocytogenes_ (aw > 0.92) [30]. In our previous studies on the effect of the addition of acid whey [18], similarly low water activity values of fermented beef sausages were obtained (<0.900), which resulted in their classification to the class aw, which indicates unfavorable conditions preventing the growth of the most popular bacteria in meat products such as _Listeria monocytogenes_, _Clostridium botulinum_ and _Escherichia coli_. Parameters such as pH and water activity are also crucial in many of the processes involved in the production of fermented sausages. These properties are related to the proteolysis process that takes place during the production of fermented meat products. As a result of these changes, peptides and amino acids are formed from muscle proteins. The enzymes that participate in these transformations include cathepsins B, D, H and L and, to a lesser extent, calpain and exopeptidases (peptidases and aminopeptides) [32]. Decrease of water activity limits the activity of muscle enzymes. According to data published by [PERSON] [33], a decrease of water activity under 0.9 strongly affects the activity of cathepsin and aminopeptides and slightly decreases the calpain activity. In our research in stuff samples (0 day), the water activity was about 0.96, which suggests that the relative activity of enzymes could be above 70%. At the end of the process, water activity decreased to 0.867-0.875, and according to [PERSON] [33], the activity of enzymes was much less intensive. The higher changes in relative activity of cathepsin and aminopeptides were observed when water activity decreased from 1 to 0.9 (relative activity of enzymes in some cases above 60% decreased) in relation to our results that showed that, in the first seven days of processing, the activity of enzymes was the most intense. Moreover, pH value at the beginning of the process (0 days) suggest that the maximal activity reached cathepsin B and L, which have shown good ability to degrade myofibrular protein and are responsible for the degradation of myosin heavy chain, actin, titin and nebulin. After one week, the pH value inactivated activity of calpain I and II (pH = 5.5); however, that was the optimal pH for activity of dipeptidylages (DPP) I and II. A further decrease in pH favors activity of cathepsin D and tripeptidases I. In this context, in the current study, the proteolysis index (PI) was an indicator of the intensity of proteolysis increased for all samples during the processing. The PI values in the tested sausages after the end of production were similar to the values published by other authors [17; 34; 35]. The highest change in PI, which suggests that the intensity of proteolysis rapidly increase, was observed in samples between the stuff sample and sample in the seventh day of manufacturing. Similar trends were observed by [PERSON] et al. [36] who, during the production of raw-ripening products, noted the highest increase in the proteolysis index after the first week of the ripening process. As in previous studies [34], no effect of acid whey supplements on the value of the proteolysis index was observed. Similarly, the use of sodium ascorbate did not significantly affect the intensity of proteolysis during the production of experimental fermented sausages. The effect of proteolysis is the formation of peptides that were assessed in this study. The experimental sausages were characterized by the peptide content from 9.69 \(\pm\) 1.19 to 11.70 \(\pm\) 0.49 mg g\({}^{-1}\) of product. As in previous studies [20], the addition of acid whey did not increase the peptide content in fermented sausages, as expected.