## 3 Results and Discussion
### Nitrites and Nitrates Content  
In the case of reducing the amount of nitrite added to meat in order to keep an acceptable curing effect, it is crucial to keep unreacted nitrite and nitrate as low as possible [5]. The highest residual nitrites level (52.1 mg/kg) in the model meat products after production was determined in the control variant (C); it was related to the dose of NaNO\({}_{2}\) applied to the meat. The residual sodium nitrite content in the M treatment was significantly lower (16.2 mg/kg) (\(p<0.05\)). The difference in the amount of residual nitrite between the C and M treatment resulted from the amount of nitrite introduced into the meat batters. Statistically, the lowest sodium nitrite level was found in the SL treatment (6.8 mg/kg) in which the mixed bacteria culture was used for meat curing. The same trend was observed after storage (Figure 1a). The factor influencing the level of residual nitrites in the product is the pH. pH value lower by 0.2 units doubles the reduction of nitrites [33]. Moreover, the level of nitrites in the SL treatment could also be influenced by bacterial activity in the raw meat batter before cooking during the 24 h period of curing the meat. _S. carnosus_ bacteria produce the nitrite reductase enzyme that takes part in the reduction of nitrites to ammonia in the anaerobic respiratory process [17; 34]. Some of the _Lactobacillus_ bacteria strains may reduce nitrites to ammonia in a process called fermentative nitrate reduction or ammonification. The second nitrite reduction type processed by lactic acid bacteria has been observed in the case of some bacteria strains that present heme independent nitrite reductase activity. In this case, the NO\({}_{2}\) bacteria reduction results in NO and N\({}_{2}\)O [14]. [PERSON] and [PERSON] [35] estimated that LAB is responsible for 30% of nitrites concentration reduction in the Bologna cooked sausage. Other research has proved that the reduction of residual nitrites concentration in the samples of fermented sausages implanted with _L. fermentatum_ totalled 76.1% of the initial nitrite's concentration [36].  
Nitrite reduction was observed during the model product storage (\(p<0.05\)). It is an issue known and described in many papers [37; 38; 39]. Significantly, the lowest nitrates content (4.4 mg/kg) after production was found in the SL treatment where the mixed bacteria culture was used in the curing process (\(p<0.05\)). A significantly higher level of nitrate was reported in the M treatment (9.7 mg/kg) and C treatment (10.0 mg/kg) (Figure 1b). The lower content of nitrates in the SL variant after heat treatment may be related to the use of these compounds by bacteria in anaerobic respiration during growth in raw meat batter before cooking. During these processes, electrons that separate from the respiration substrate are connected to nitrates by the nitrate reductase enzyme and create nitrites [14]. Nitrate content in the SL treatment was reduced during storage (\(p<0.05\)). After four weeks of storage, a reduction of the amount of nitrates was observed in the M and C treatments to the levels of 5.4 mg/kg and 3.9 mg kg, respectively. After eight weeks of storage, the nitrate level increased to 6.9 mg/kg in the M treatment and 7.1 mg/kg in the C treatment. Nitrate reduction in the product may happen with the use of bacteria enzymes. The microbiological analysis showed that total aerobic bacteria count (ACC) was at the level of 10\({}^{2}\) cfu/g in all of the experimental treatments after cooking and storage. The nitrate increase observed after storage in the M and C treatments are most likely the result of nitrite residual oxidation [4]. In the SL variant, the nitrates level did not increase after eight weeks of storage, which could be the result of the observed redox potential stability (Table 1, Figure 1b).