## 4 Discussion  
Our obtained results regarding the formation of TVB-N during storage from \(-2\) to \(-3\)\({}^{\circ}\)C can be explained by the effects of endogenous or bacterial proteolytic enzyme systems [31]. The TVB-N values in all 17 tested samples (Table 3) were very low and did not exceed the limits of acceptability during the 21 days of superchilled storage. This means that, at all regimes of superchilling, the fish preserved its freshness to a satisfactory degree. In accordance with the obtained results, [32] reported a possible shelf life of 21 days for frozen grass carp (_Ctenopharyngodon idellus_). From the results presented in Table 3, it can be seen that the combination of factors in sample 9 (in the center of the experiment; T = \(-12.5\)\({}^{\circ}\)C; \(\
u\) = 5 m s\({}^{-1}\); D = 80 \(\mu\)m) TVB-N were with the lowest values of 23.23 mg N\({}_{2}\) 100 g\({}^{-1}\), while the fish in sample 1 (T = \(-20\)\({}^{\circ}\)C; \(\
u\) = 3 m s\({}^{-1}\); D = 60 \(\mu\)m) had the highest values of 27.88 mg N\({}_{2}\) 100 g\({}^{-1}\). The influence of the three examined variables, the air temperature (T), the airflow velocity (\(\upsilon\)), and the packing layer thickness (D) to the total viable count (TVC) of golden rainbow trout during the 21 days of superchilled storage showed different values in all seventeen studied superchilling regimes. The lowest TVC was found in the superchilled trout--sample 9 = 4.13 log cfu g\({}^{-1}\), which is below the acceptable limit of 7.00 log cfu g\({}^{-1}\)[33]. It was established that only the factor of air temperature (T) significantly influences microflora growth (Figure 3b). The lower temperature can suppress and slow down microbial growth in the superchilled fish. Low temperature helps to partially freeze most of the water in the fish muscle tissue [34]. This reduces water activity and makes the remaining free water hardly accessible to microorganisms. The metabolic processes occur at a much slower pace, which is the main reason for the low degree of bacterial microflora development [35]. The ultra-fast air-superchilling in our study has proven to be successful in all analyzed samples. The superchilling successfully inhibited the growth of microorganisms during 21 days of storage, thus preserving freshness and prolonging the shelf life of golden rainbow trout. The data obtained from the microbiological analyses of all experimental samples are in full agreement with the results of the sensory analysis of the roasted golden rainbow trout and with the indicators TVB-N and biogenic amines. Similar to our results have been published by [PERSON] [36], reporting a shelf life of 20 days and a reduced total bacterial colony count in fillets of Atlantic salmon (_Salmo salar_). All samples of grilled golden rainbow trout were evaluated with high complex scores after 21 days at superchilled storage. These results indicate that the sensory characteristics of fish were well preserved at all analyzed ultra-fast air regimes of superchilling, although sample 9 of golden rainbow trout received the highest estimated sensory score after grilling. Lower but very similar sensory scores were estimated for samples 4 and 8. The combination of sufficiently low temperatures and a high rate of ultra-fast air-superchilling allows for the production of superchilled golden rainbow trout with attractive sensory characteristics. The sensory scores evaluated for the grilled golden rainbow trout served as a parameter indicating fish freshness and could significantly affect the shelf life. The evaluated high sensory scores of grilled fish confirm that under superchilled conditions, it can be stored for up to 3 weeks after catching. Similar to ours, the results were reported by [PERSON] et al. [37], who reached a 20-day shelf life of Nile tilapia (_Oreochromis niloticus_) fillet stored at \(-1\)\({}^{\circ}\)C.  
The air temperature most strongly affected the TVB-N formation in the golden rainbow trout muscle tissue. It was followed by the factor airflow rate (Figure 2a).