## 2 Results and Discussion
### Relationship between LF-NMR Parameters (T\({}_{2b}\), T\({}_{21}\) and T\({}_{22}\)) and VOCs  
The relationship between LF-NMR parameters and VOCs was investigated by RDA (Figure 5) and Pearson correlation coefficients (Table 2). RDA showed that T\({}_{2b}\) was significantly correlated with acetone, 2-undecanone, 1-hexanol and 1-nonanol (\(p<0.05\)). Pearson correlation coefficient results showed extremely significant correlations between T\({}_{21}\) and hexanal (r = \(-0.80\)), 1-hexanol (r = \(-0.71\)), 1-octen\(-3\)-ol (r = \(0.88\)) and 1-penten-3-ol (r = \(0.82\)). T\({}_{22}\) was positively correlated with nonanoic acid, ethyl ester (\(p<0.05\)), while T\({}_{22}\) was negatively correlated with naphthalene (\(p<0.05\)). With the extension of storage time, T\({}_{21}\) decreased significantly while T\({}_{22}\) increased, which resulted in an increase in the metabolic rate and microbial growth. The myofibrils tissue became loose and intramuscular connective of the skelemin damaged due to the value of free water increased during storage, so that microorganisms grew quickly to produce numerous VOCs including ethyl ester, 1-hexanol, nonanoic acid and 1-nonanol [4; 38], indicating that accelerated quality deterioration [7]. Therefore, the results showed that water dynamics were significantly correlated with the volatile compounds, which could be applied to evaluate the quality of bigeye tuna.  
Figure 4: Changes in haematoxylin and eosin (HE)-stained muscle tissues of bigeye tuna stored for 0 days (**a**); tuna stored at 0 \({}^{\circ}\)C (**b**,**c**) for 3 days and 4 \({}^{\circ}\)C (**d**,**e**) for 6 days.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **T2b** & **T21** & **T22** \\ \hline Hexanal & \(-\)0.25 & \(-\)0.80 ** & 0.39 \\ Heptanal & \(-\)0.18 & \(-\)0.21 & 0.48 \\ Octanal & \(-\)0.17 & \(-\)0.40 & 0.41 \\ Nonanal & \(-\)0.02 & \(-\)0.34 & 0.18 \\
2,6-Nonadienal,(E,Z)- & \(-\)0.14 & \(-\)0.38 & 0.43 \\ Tetradecanal & \(-\)0.14 & \(-\)0.38 & 0.43 \\ Propanal & \(-\)0.06 & \(-\)0.52 * & 0.23 \\
4-Heptenal, (Z)- & \(-\)0.16 & \(-\)0.40 & 0.44 \\ Pentadecanal- & \(-\)0.16 & \(-\)0.40 & 0.44 \\ Acetone & 0.53 * & \(-\)0.21 & \(-\)0.46 \\
2-Heptanone & 0.22 & \(-\)0.46 & \(-\)0.01 \\
2-Nonanone & \(-\)0.11 & \(-\)0.47 & 0.39 \\
2-Undecanone & \(-\)0.60 * & \(-\)0.62 * & 0.56 * \\
2,3-Pentanedione & 0.05 & \(-\)0.15 & \(-\)0.21 \\
1-Pentanol & 0.02 & \(-\)0.54 * & 0.28 \\
1-Hexanol & \(-\)0.54 * & \(-\)0.71 ** & 0.51 \\
1-Octen-3-ol & 0.01 & 0.88 ** & \(-\)0.16 \\
1-Heptenal & 0.03 & \(-\)0.56 * & 0.28 \\
1-Octanol & \(-\)0.04 & \(-\)0.38 & 0.37 \\
2-Octen-1-ol, (E)- & \(-\)0.17 & \(-\)0.42 & 0.43 \\
1-Nonanol & 0.55 * & \(-\)0.25 & \(-\)0.39 \\
2-Penten-1-ol, (Z)- & \(-\)0.05 & \(-\)0.43 & 0.36 \\
1-Penten-3-ol & 0.27 & \(-\)0.82 ** & \(-\)0.33 \\ Nonanoic acid, ethyl ester & \(-\)0.40 & \(-\)0.21 & 0.63 * \\ Hexanoic acid & \(-\)0.03 & \(-\)0.56 * & 0.31 \\ Benzaldehyde & 0.29 & 0.44 & \(-\)0.27 \\ Naphthalene & 0.37 & \(-\)0.06 & \(-\)0.65 ** \\ Naphthalene,2 methyl- & 0.05 & 0.43 & 0.28 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Pearson’s correlation analysis and levels of significance for correlations between LF-NMR parameters (T2b, T21 and T22) and VOCs of bigeye tuna.  
Figure 5: Redundancy analysis (RDA) of T2 transverse relaxation and VOCs.