## 3 Results and Discussion
### TMA, TVB-N, and TBARS  
Table 3 shows the changes in TVB-N, TMA, and TBARS levels in yellowtail muscle during storage at different temperatures. TVB-N in OM and DM increased significantly during storage under all storage conditions, except for OM in ice, whereas no large suppressive effect of decreasing temperature on the increase in TVB-N was observed. However, it did not exceed the spoilage threshold (acceptable limit) after storage (25-30 mg/100 g) [34; 35; 36; 37]. No marked differences in TVB-N were observed between OM and DM when the same storage temperatures were compared. These findings differ from those of sea bass and greater ambjack, in which increases in TVB-N during storage were suppressed by storage at lower temperatures [32; 38]. This discrepancy may be due to differences in fish species, origin, partial freezing conditions, and contaminating bacteria, or because the storage period was within the range not exceeding the spoilage threshold.  
The TMA levels significantly increased under all storage conditions. OM did not exceed the acceptable TMA limit of 50-100 ug/g [34; 36]; however, DM exceeded these limits on days 6, 7, and 7 in refrigerated, ice, and SC storage, respectively. This indicates that the temperature difference between refrigeration and SC storage was insufficient to suppress TMA production in DM and is probably the result of enhanced enzyme activity with minimal reduction in TMAO reductase activity due to partial freezing during SC storage [39]. In other words, in DM, the increase in TMA levels during storage may be due to endogenous enzymes rather than bacterial proliferation. On the other hand, in OM, lower-temperature storage was found to have an inhibitory effect on the increase in TMA. Storage of rohu and mackerel at lower temperatures also inhibited TMA formation [38; 40], supporting the results of the present study.  
The TBARS levels in OM and DM also increased significantly during storage, with no notable differences between adjacent storage periods under different storage conditions, indicating that TBARS formation was not suppressed at lower temperatures. [PERSON] and [PERSON] noted that ice crystals formed during SC storage can promote autolysis as well as enzymatic and chemical reactions by damaging cell membranes and releasing oxidation-accelerating enzymes [41]. Thus, although SC storage inhibited spoilage by microorganisms, partial freezing did not suppress some biochemical changes. In pre-spoilage gilthead seabram fillets, storage at \(-1\)\({}^{\circ}\)C was found to result in a greater increase in TBARS than storage at 3 \({}^{\circ}\)C [42]. In our previous study, storage in ice delayed the increase in TBARS in pre-spoilage yellowtail OM and DM [10]. The difference between  
\begin{table}
\begin{tabular}{l c c c c} \hline  & **Muscle Type** & **3 \({}^{\circ}\)C** & \(\Phi\) \({}^{\circ}\)C & \(-\)**3 \({}^{\circ}\)C** \\ \hline Mesophilic & OM & 1.50 & 0.64 & 0.32 \\ bacteria & DM & 1.38 & 0.51 & 0.28 \\ _Brochthrix thermosphacta_ & OM & 1.34 & 0.55 & 0.32 \\  & DM & 1.11 & 0.44 & 0.18 \\  & OM & 1.77 & 0.78 & 0.37 \\ Enterobacteriaceaeae & DM & 1.66 & 0.62 & 0.37 \\  & OM & 1.27 & 0.81 & 0.30 \\ _Aeromonas_ spp. & DM & 1.34 & 0.76 & 0.30 \\  & OM & 1.22 & 0.74 & 0.28 \\ Marine bacteria & DM & 1.06 & 0.55 & 0.21 \\  & OM & 1.31 & 0.69 & 0.30 \\  & DM & 0.97 & 0.44 & 0.23 \\ H\({}_{2}\)S producing & OM & 1.24 & 0.58 & 0.05 \\ bacteria & DM & 1.17 & 0.44 & 0.09 \\ \hline \end{tabular} OM, ordinary muscle in dorsal part; DM, dark muscle.  
\end{table}
Table 2: Linear growth rate (\(k\)) of bacteria in raw yellowtail muscles stored at different temperatures (1/day).  
these results and those of the present study may be due to the partial freezing mentioned above and the storage period (before and until spoilage).