# Impact of Cooking Processes on Volatile Flavor Compounds and Free Amino Acids in Fish Sauce
## 3 Results and Discussion
### FAAs of Fish Sauces  
Seventeen FAAs were identified in all fish sauce samples, and they are considered to significantly contribute to the flavor of the fish sauce (Table 2). As shown in Table 2, as heating time increased, the total FAAs content in the boiled sample initially increased, then decreased, but overall showed a significant increase. This suggests that heating promotes protein hydrolysis in fish sauce, resulting in the release of more amino acids. These findings agree with previous research on freshwater crayfish [40]. In stir-fried fish sauce, the total FAAs content initially decreases, then increases, and finally decreases again. This may result from the increased heating temperature, which promotes oxidative damage, amino acid side chain modification, and aromatic amino acid modification, leading to greater FAAs loss [44]. Consequently, the total amino acids content in F10 decreases significantly over a short period. However, the abundant protein in the fish sauce aggregates and gels at high temperatures, forming a three-dimensional protein network on the pan surface [45]. This protects the FAAs in the fish sauce, leading to a significant increase in total FAAs content in F30. However, this process hinders the formation of volatile flavor compounds, leading to the lowest concentration of key flavor compounds, such as trimethylamine, in F30. As heating time increased, the temperature of the fish sauce rose, resulting in a significant decrease in FAAs content. Additionally, due to the varying heat resistance of amino acids, after 60 min of cooking, the levels of umami and sweet amino acids decreased significantly compared to unheated fish sauce, whereas the levels of bitter and bittersweet amino acids increased.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Volatile Compounds**} & \multirow{2}{*}{\begin{tabular}{c} **Odor Threshold** \\ **(\%/kg)** \\ \end{tabular} } & \multicolumn{5}{c}{**OAVs**} & \multirow{2}{*}{\
\begin{tabular}{c} **Odor Description** \\ **U** \\ \end{tabular} } \\  & & **B10** & **B30** & **B60** & **F10** & **F30** & **F60** \\ \hline Trimethylamine & 2.4 & 251.75 & 182.94 & 432.73 & 257.00 & 288.73 & 152.23 & 174.00 & Fishy \\ \(\gamma\)-Nonalactone & 9.7 & 0.99 & 1.36 & 1.55 & 1.66 & 1.05 & ND & ND & Sweet, creamy, coconut-like \\ \multirow{2}{*}{
\begin{tabular}{c} Phenylethyl alcohol \\ Benzene acetaldehyde \\ Nonanal \\ \end{tabular} } & 45 & 1.40 & 1.95 & 2.14 & 1.53 & 1.92 & ND & ND & Honey, rose \\ Benzene acetaldehyde & 4 & 17.36 & 20.07 & 23.82 & 17.78 & 27.43 & 14.81 & 22.84 & Rosy-like \\ Nonanal & 1 & 4.25 & 13.15 & 12.17 & 6.50 & 9.63 & 8.22 & 7.43 & Rose, fresh, fatty \\ Decanal & 0.1 & 22.20 & 38.90 & 69.80 & 49.40 & 235.50 & 227.30 & 293.90 & Fatty, floral, and green \\ Methional & 0.4 & 30.98 & 36.05 & 37.35 & 68.35 & 97.85 & 24.25 & 57.40 & Cooked potato \\
2-Ethyl-5-methylpyrazine & 0.4 & ND & 23.40 & 40.60 & ND & ND & ND & ND & Potatees, roasted nuts \\
2,6-Diethylpyrazine & 6 & 2.02 & 2.59 & 2.21 & 1.93 & 1.81 & ND & ND & roasted, nutty, sweet \\
2,3,5-Methyl pyrazine & 0.4 & 15.58 & 27.23 & 75.55 & 46.48 & 43.48 & 14.25 & 31.00 & Nuts, chocolate, coffee \\ Total & & 346.51 & 347.64 & 697.91 & 450.63 & 707.40 & 441.06 & 586.57 & \\ \hline \hline \end{tabular}  
* ND: Not detectedND. OAVs: Odor activity values. Odor threshold in water and odor description found in the literature and liber [10,16,17,23,27,39,40,41,42,43].  
\end{table}
Table 1: Key volatile compounds in fish sauces following different cooking processes.