## 3 Results and Discussions
### Odor Characteristics
Interestingly, the relative contents of many terpenoids, contributing to lemon-like, woody, or floral notes, were noticeably higher in the samples fermented with LAB than in the samples prepared by spontaneous fermentation. It was suggested that during the fermentation of Zhayu, the metabolism of LAB could promote the formation of terpenoids. A similar phenomenon was also found in Suan yu, another kind of fermented fish product [6]. The enriched terpenoids by LAB-inoculated fermentation would enhance the overall aroma characteristics of the fermented fish products. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Compounds** & **RI** & **Identification** & **Odor** & \multicolumn{3}{c}{**Odor Threshold**} & \multicolumn{3}{c}{**Relative Concentration (log/kg)**} \\ \cline{4-9}  & & & & (wig/kg) & **SF** & **L.P.** & **P.A. ** & **EP. ** \\ \hline \(\alpha\)  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Compounds** & **RI** & **Identification** & **Oder** & **Oder Threshold** & \multicolumn{3}{c}{**Relative Concentration (log/kg)**} \\  & & & & **(log/kg)** & **SF** & **L.P.** & **P.A. ** & **P.P. ** \\ \hline Noncentning compounds & & & & & & & \\
2-methylpyrazine & 1258 & MS, RII, & multy, cocou-like & 60–100,000\({}^{\circ}\) & 0.89 \(\pm\) 0.17\({}^{\circ}\) & 0.52 \(\pm\) 0.004\({}^{\circ}\) & 0.68 \(\pm\) 0.020\({}^{\circ}\) & 0.64 \(\pm\) 0.001\({}^{\circ}\) \\
2-3-dimethylpyrazine & 1399 & MS, RII, & multy, cocou-like & 250-35,000\({}^{\circ}\) & 0.37 \(\pm\) 0.004\({}^{\circ}\) & 0.13 \(\pm\) 0.01\({}^{\circ}\) & 0.24 \(\pm\) 0.02\({}^{\circ}\) & 0.11 \(\pm\) 0.02\({}^{\circ}\) \\
2-ethyl-hydrazine & 1377 & MS, RII & masted & 800-800\({}^{\circ}\) & 0.46 \(\pm\) 0.08\({}^{\circ}\) & 0.28 \(\pm\) 0.001\({}^{\circ}\) & 0.48 \(\pm\) 0.007\({}^{\circ}\) & 0.29 \(\pm\) 0.01\({}^{\circ}\) \\ trimethylpyrazine & 1399 & MS, RII, & baked potato & 400-800\({}^{\circ}\) & 0.13 \(\pm\) 0.01\({}^{\circ}\) & 0.11 \(\pm\) 0.01\({}^{\circ}\) & 0.14 \(\pm\) 0.02\({}^{\circ}\) & 0.11 \(\pm\) 0.01\({}^{\circ}\) \\ tetramethylpyrazine & 1472 & MS, RII, & fermented, & 1000-10,000\({}^{\circ}\) & 0.66 \(\pm\) 0.05\({}^{\circ}\) & 0.49 \(\pm\) 0.01\({}^{\circ}\) & 0.64 \(\pm\) 0.04\({}^{\circ}\) & 0.48 \(\pm\) 0.02\({}^{\circ}\) \\
4-methyl-5-thiazolocethanol & 2275 & MS, RII & masty & 10,800\({}^{\circ}\) & 0.20 \(\pm\) 0.02\({}^{\circ}\) & 0.10 \(\pm\) 0.02\({}^{\circ}\) & 0.14 \(\pm\) 0.05\({}^{\circ}\) & 0.06 \(\pm\) 0.00\({}^{\circ}\) \\ \hline \multicolumn{7}{c}{Notes Different between between different differences in the same row (\(y\) + 0.05), MS, mass spectrum appear with those of the authentic compound; RI, compound was confirmed by the retention index of the compound standard; RI, compound was identified according to the retention index from the NIST Chemistry Workshop; N-D, not detected. \({}^{\star}\) Threshold adapted from [PERSON] et al. [(4)]. \({}^{\star}\) Threshold adapted from [PERSON] et al. [(4)]. \({}^{\star}\) Threshold adapted from [PERSON] and associating (two papers); \({}^{\star}\) threshold adapted from [PERSON] et al. [(38)]. \({}^{\star}\) Threshold adapted from [PERSON] et al. [(4)]. \({}^{\star}\) Threshold adapted from [PERSON] et al. [(4)]. For other compounds, the contents of ketones in LAB-inoculated Zhayu samples were significantly lower than those in the control, especially 2,3-butanedione with a buttery note and 3-hydroxy-2-butanone with a yogurt-like note. Not surprisingly, the LAB-inoculated fermentation dramatically increased the acids' contents in the Zhayu samples compared with the control, which was coincident with the sensory evaluation results (Figure 4d). Additionally, the Zhayu samples prepared with _L. plantarum_ contained the highest acetic acid, butanoic acid, and 4-methylentanoic acid. Meanwhile, esters, which were derived from the microbial esterification of acids with alcohols, also showed higher contents in Zhayu samples fermented with LAB than in the control.