## 3 Results and Discussion
### Volatile Compounds
It has a low detection threshold (1.5 \(\upmu\)g/kg), which contributes to the mushroom aroma and can be eradicated during the heating process [28]. This description is related to our results, which found that 1-Octen-3-ol was found at lower amounts when applied with a higher temperature and longer SV cooking time. Moreover, the lower level of this compound, particularly when processed with more severe SV conditions, may improve the flavor/odor of cooked fish by lowering the fishy or rancid off odors occurring in fresh meat. All SV-cooked tilapia with an N-containing compound as the major compound, accounts for more than 25% of all volatiles. Only four nitrogen-containing compounds, including trimethylamine, 2,6-dimethylpyrazine, trimethylpyrazine and 2-ethyl-3,5-dimethylpyrazine, were detected in all samples. It was found that trimethylamine was the most abundant volatile compound in SV-cooked tilapia, corresponding well with the reports by [PERSON] et al. [29] and [PERSON] et al. [28]. In this study, trimethylamine was found at the highest level in the control and the 50.30 sample, accounting for 30.25 and 28.42%, respectively. Among all SV-cooked samples, this compound was found at a lower amount when the temperature and time for cooking was increased, which was lower than the control. Trimethylamine has been reported in most fish species, contributing to the \"fishy\" aroma note with a low detection threshold. A high level of TMA lends an undesirable odor to seafood products [29]. The lower amount found in SV-cooked samples, compared with the control, may indicate that SV cooking could prohibit the development of undesirable odor/aroma compounds generated during heating better than the traditional method. The other three N-containing compounds found in the samples were pyrazine derivatives. Our results showed that the control contained higher pyrazine derivatives than the SV-cooked samples. Pyrazines were produced by the Maillard reaction and the thermal degradation reaction. These compounds were generally prevalent in thermally processed meat, particularly roasted meat, which is responsible for the nutty, earthy and fruity taste [18]. However, it accumulated in quite a low amount; thus, it could not be the main compound responsible for cooked/boiled fish. Five S-containing compounds were detected. Among them all, methanethiol was found to be dominant (4.11-15.15%). The results indicated that this compound decreased when the temperature or time of SV-cooking increased. This corresponded to the study by [PERSON] et al. [33] and [PERSON] et al. [28] who reported that the formation of methanethiol in cooked tilapia and herring initially increased to a maximum, and then declined as thermal time increased, respectively. During heating, methanethiol, the breakdown product of aldehyde, is generated and plays a role as a precursor to forming numerous sulfur compounds such as dimethyldisulphide [33]. [PERSON] et al. [28] noted that the S-containing compound has very low odor thresholds and potent flavor characteristics, thus playing a key role in the aroma of cooked meat. Moreover, limonene as well as two furans including 2-pentylfuran and 2-methylfuran were detected in the samples. However, in most cases, furans do not contribute a lot to the overall aroma in most fish species, particularly boiled fish. This was because the concentration found in boiled fish was below the detection threshold, as reported by [PERSON] et al. [34].