## 3 Results and Discussion
### Physicochemical and Microbiological Parameters
For the control samples, the value of this parameter decreased statistically significantly (\(p<0.05\)) after 72 h of storage, but did not fall below 6.00. Similar results to the increase in pH values after their initial decrease have been presented by other authors [45]. This is because after fish killing, changes in pH values also occur as a result of biochemical post-mortem processes due to the breakdown of glycogen to lactic acid, as observed in the control samples. These changes are more pronounced in aquacultured fish, which have a higher supply of energy-rich compounds compared to wild fish. Therefore, it can be concluded that in our experiment, the decreasing trend in pH values during filled storage was probably amplified with increasing concentrations of sumac preparation. This can be concluded from the results of the existence of statistically significant differences (\(p<0.05\)) between the pH values depending on the increasing concentrations of sumac spices applied to the surface of the fillets, where differences were found after 24 h between the control samples or samples with 0.5% sumac (T1) and samples with the application of sumac with a concentration of 1.5% and 2.5% (T2 and T3) of the product, respectively. The increase in the pH values during the experiment could be related to the development of bacteria with proteolytic enzymes involved in the degradation of proteins and the formation of total volatile nitrogen bases (TVB-N), which are alkaline in nature [46]. The fillets with cut muscle bones are specially prepared on machines equipped with circular knives placed at a distance of approximately 2-3 mm from each other in order to cut the muscle of the fillet down to the skin, breaking these bones and thus minimising the risk of injury to the mucous membranes of the digestive tract of the consumers. However, a significant increase in the surface area of the fillets entails the possibility of spreading surface contamination of the fillet into the cut muscle, where microorganisms find optimal conditions for growth and multiplication due to the appropriate composition of the internal tissue environment. There is no mandatory limit for APC for fresh freshwater fish that should not be exceeded; however, for freshwater fish, some sources indicate a maximum of \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Storage Hours**} & \multicolumn{4}{c}{**Sumac Concentration**} \\ \cline{2-5}  & **0\% (T0)** & **0.5\% (T1)** & **1.5\% (T2)** & **2.5\% (T3)** \\ \hline \multicolumn{5}{c}{a*} \\ \hline
0 * & \(-0.24\pm 0.73\) B  & \(-0.32\pm 0.70\) B  & \(-0.51\pm 0.39\) B  \\
24 & 0.68 \(\pm\) 0.85 ABc  & \(3.73\pm 0.72\) AB  & \(5.66\pm 1.50\) AA  & \(6.25\pm 0.86\) AA  \\
72 & 1.59 \(\pm\) 1.02 ABc  & \(4.09\pm 1.50\) AA  & \(4.93\pm 1.29\) AA  & \(5.95\pm 0.55\) AA  \\ \hline \hline \end{tabular}
\end{table} 
Table 5: _Cont._up to 7 log CFU\(\cdot\)g\({}^{-1}\)[47]. Considering the expected higher APC values in the input samples that we demonstrated in our experiment, the application of seasonings with antimicrobial and antioxidant effects seems to be highly desirable [48]. This is because by cutting the fillet, the fats present inside the muscle are exposed directly to the oxygen present in the air. Unfortunately, a disadvantage of using dry natural seasonings may be the potential presence of contaminating microorganisms, which may be activated in an environment with appropriate water activity and pH values and secondarily increase the contamination of the tissues to which they have been applied [49]. The decrease in pH values 24 h after application of 1.5% and 2.5% (T2 and T3) sumac spices to carp fillets was probably the reason for the statistically significantly (\(p<0.05\)) lower APC values found. However, after 72 h, APC values increased significantly and no statistically significant differences were found between the contamination intensity of control and experimental fillets with different sumac concentrations.