## 3 Results and Discussion
### Volatile Compounds  
A total of 43 volatile compounds including aldehydes (8), ketones (8), alcohols (7), N-containing compounds (4), S-containing compounds (6) and others (3) were detected in various SV-cooked tilapia (Table 2). Overall, as expected, each sample varied in the proportion of volatile compounds, evidencing the influence of temperature and time on volatile profiles formed during SV cooking. Normally, aldehydes and ketones are secondary products from lipid oxidation [28]. In depth, aldehydes are thermal degradation products of fats, whereas ketones are generated by microbial enzymatic actions on either lipids or amino acids, as well as by the Maillard reaction [29]. From the results, total abundance of aldehydes, i.e., 2,3-methylbutanal, hexanal, heptanal, 2-ocretal, etc. of SV-cooked tilapia tends to decrease as the temperature and time for SV cooking increased. Furthermore, the total abundance of ketones, i.e., 2-butanone, 2-heptanone, 2-decanone, etc. tended to increase when processed with more severe conditions. The results stated that lipid oxidation took place during SV-cooking. However, because of the quite low temperature of SV cooking (50-60 \({}^{\circ}\)C), the aldehyde generated by thermal degradation of lipids may occur at a lower level in all samples. [PERSON] et al. [22] reported that unsaturated acyl groups were slightly oxidized during SV cooking and led to the formation of ketones, alcohols, aldehydes and acids. Compared to aldehydes, ketones were governed and applied in more severe SV conditions. Among all ketones, acetoin was found to be dominant in all samples, accounting for 6.78-12.49%. Acetoin is responsible for the buttery, sweet, cream or classified as desirable oily note in meat products, as reported by [PERSON] et al. [30]. The diketones produced during the process are the products of the primary stage of the Maillard reaction, which can balance the flavor of meat [29]. Thus, the development of acetoin when processed with higher temperature and longer processing time of SV cooking may be associated with the improvement of some  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Category** & **Name** & **50-30** & **50-45** & **50-60** & **60-30** & **60-45** & **60-60** & **Control** \\ \hline Umami & Aspartic acid (Asp) & 5.45 \(\pm\) 1.01 \({}^{\mathrm{h}}\) & 7.78 \(\pm\) 1.22 \({}^{\mathrm{a}}\) & 8.99 \(\pm\) 1.66 \({}^{\mathrm{a}}\) & 9.33 \(\pm\) 2.02 \({}^{\mathrm{a}}\) & 7.12 \(\pm\) 1.63 \({}^{\mathrm{a}}\) & 8.59 \(\pm\) 1.67 \({}^{\mathrm{a}}\) & 7.14 \(\pm\) 1.44 \({}^{\mathrm{a}}\) \\  & Glutamic acid (Glu) & 30.66 \(\pm\) 2.99 \({}^{\mathrm{h}}\) & 30.33 \(\pm\) 2.05 \({}^{\mathrm{h}}\) & 36.06 \(\pm\) 3.66 \({}^{\mathrm{a}}\) & 33.21 \(\pm\) 3.41 \({}^{\mathrm{a}}\) & 36.77 \(\pm\) 2.06 \({}^{\mathrm{a}}\) & 38.02 \(\pm\) 1.99 \({}^{\mathrm{a}}\) & 34.34 \(\pm\) 3.06 \({}^{\mathrm{a}}\) \\  & Total & 36.11 & 38.11 & 45.05 & 42.54 & 43.89 & 46.61 & 41.48 \\ \hline Sweet & Alanine (Ala) & 25.51 \(\pm\) 2.68 \({}^{\mathrm{h}}\) & 25.08 \(\pm\) 4.55 \({}^{\mathrm{h}}\) & 23.23 \(\pm\) 2.16 \({}^{\mathrm{h}}\) & 27.12 \(\pm\) 2.44 \({}^{\mathrm{h}}\) & 26.66 \(\pm\) 2.19 \({}^{\mathrm{h}}\) & 33.99 \(\pm\) 3.03 \({}^{\mathrm{a}}  
flavors in the final product. In general, ketones contain high odor threshold values [31]. Therefore, their aroma contributions might be minimal, even though their flavor notes are generally desirable. Alcohol was found at moderate proportions in all SV-cooked tilapia (14.42-21.42%). Alcohol is also generated by lipid oxidation, and their thresholds are normally high, so they do not make great contributions to meat odor/flavor [28]. Among all alcohols, 1-Octen-3-ol was found to be the dominant alcohol in all samples, accounting for 10.12-17.06%. 1-Octen-3-ol, an unsaturated alcohol, is one of the main volatiles detected in fresh fish together with hexanal [29]. [PERSON] et al. [32] reported that 1-octen-3-ol strongly contributed to the fishy or rancid off-odors in Asian seabass meat.