## 3 Results and Discussion  
The results of the HPP treatments are presented in Tables 1 and 2. The numbers of _Listeria monocytogenes_ colonies in inoculated samples, both in cold-smoked and in warm-smokedfish samples, were within the official limit of the Regulation (EC) No. 2073/2005 (100 cfu/g) after the pressure treatment at 600 MPa in every analysed timepoint. A significant difference (\(p<0.05\)) was observed between inoculated nontreated cold-smoked fish samples and inoculated cold-smoked fish samples treated at 600 MPa at the one-day analysis point. In addition, a significant difference (\(p<0.05\)) between inoculated nontreated warm-smoked fish samples and inoculated warm-smoked fish samples treated at 600 MPa was observed at the 28-day analysis point. _L. monocytogenes_ was not detected in control samples with no added _L. monocytogenes_ and no HPP treatment (the results are not presented in the tables), indicating the good microbial quality of the raw material used in this study. The amount of _L. monocytogenes_ was observed to decrease during the storage time in inoculated cold-smoked rainbow trout samples in both nontreated and treated samples. In a study by [PERSON] et al. (2016), HPP treatment at a pressure over 414 MPa for 5 min reduced the amount of _Listeria_ by more than four logarithmic times in minced rainbow trout samples, and NaCl was found to further increase the effectiveness of the treatment. In this study, the reduction of the amount of _L. monocytogenes_ was the highest (3.8-log) in the cold-smoked fish samples at the one-day analysis point for the treatment at 600 MPa. However, the amount of _L. monocytogenes_ increased during the storage time in all inoculated warm-smoked fish samples, although the growth was weaker in samples with higher-pressure treatments. Thus, the growth of _Listeria_ was observed in all (nontreated and treated) warm-smoked fish samples during storage time. The HPP treatment at 600 MPa for 3 min is not sufficient to destroy _L. monocytogenes_ in warm-smoked rainbow trout samples if the fish material is heavily contaminated with _Listeria_. Similar findings were detected in a study by [PERSON] et al. (2013), as after 41 storage days the amount of _Listeria_ in HPP-treated mild-smoked rainbow trout samples reached almost the same level as the _Listeria_ amount in non-HPP-treated samples. These results clearly indicate that _Listeria_ can grow effectively at refrigerator temperatures. Sodium chloride (NaCl) is one of the main ingredients in RTE fish products. NaCl is the factor that gives the products their characteristic flavour, taste, colour, and texture. For example, NaCl, liquid smoke and drying, vacuum packing, and low storage temperature were able to control _L. monocytogenes_ in cold-smoked salmon samples ([PERSON] et al., 2013). Thus, it seems that a high NaCl concentration can effectively decrease the amount of _L. monocytogenes_ in cold-smoked fish samples, even in the non-HPP-treated samples. Furthermore, smoke extract could be an additional factor that could be used to inhibit the growth of _Listeria_ in \begin{table}
\begin{tabular}{c c c c} \hline
**Treatment/Storage Time** & **1 Day** & **14 Days** & **28 Days** \\ \hline
**Nontreated** & 5.5 \(\pm\) 0.1 a & 5.5 \(\pm\) 0.7 & 4.2 \(\pm\) 1.5 \\
**HPP treated at 200 MPa** & 5.4 \(\pm\) 0.2 & 5.2 \(\pm\) 0.7 & 3.7 \(\pm\) 0.8 \\
**HPP treated at 400 MPa** & 4.6 \(\pm\) 0.4 & 4.4 \(\pm\) 0.5 & 2.5 \(\pm\) 0.9 \\
**HPP treated at 600 MPa** & 1 a & 1 & 1 \\ \hline \end{tabular} Values are the mean \(\pm\) standard deviations of three replicates. Values followed by the same letter are significantly different (\(p<0.05\)). 1 Below the detection limit (100 cfu/g).  
\end{table} 
Table 1: Numbers (log\({}_{10}\) cfu/g) of _Listeria monocytogenes_ colonies in inoculated cold-smoked rainbow trout samples at three (1, 14, and 28 days) different storage timepoints.