## 4 Metabolomics for Metabolite Detection in Aquatic Food Products  
### Muscle Quality and Taste  
In aquatic food products, quality assurance is a significant aspect and has gained special attention. For instance, metabolomics approaches could be engaged for fish post-harvest quality control [102; 103; 104]. In these studies, investigations on fish quality established the major targeted metabolomics as LC-MS, HR-MAS-NMR, GC-MS, and DART-HR-MS. In salmonids, these methods were used to quantify total lipids, omega-3, DHA, and EPA content [23; 105], validate farming of fish, allocate origin [106; 107; 108], classify K-value and trimethylamine nitrogen (TMA-N) [109], and types of lipids during cold storage, which are indicators of quality and freshness [110]. [PERSON] et al. [111] implemented a near-infrared spectroscopic to authenticate \(D\). _labrax_ fillets, which were dependent on their cultivation system (wild-caught vs. farmed), farming system, and geographic source. Statistical analysis matched to spectral AAs and peptide absorption and region could illustrate correctly (at 100%) cultivated from wild fish and authenticated fish at 67% (general), 80% semi-intensive, and 100% (intensive growing). Collected from different European regions, the fatty acids of \(D\). _labrax_ were effectively distinguished by spectral data [111]. This investigation stressed the capacity of metabolomics for rapidly determining the origin, distinguishing wild-harvested from type of farm, and battling fraudulent substitution and mislabeling of fish products [112; 113]. [PERSON] et al. [114] developed a \({}^{1}\)H-NMR approach for _S. salar_ authentication and classification. The platform permitted to identify hypoxanthine, individual AAs, FAs, lactate, and anserine, which are indicative of nutritional profile and overall muscle quality. Based on targeted systems employed to differentiate between wild and farmed salmon, \({}^{1}\)H-NMR was utilized to investigate the impact of salmon feed on wild _Pollachius virens_ (saithe) [115]. The metabolomics of muscle and liver tissues exposed high levels of glutamine, alanine, lactate, and glutamate in wild saithe caught around salmon farms. In addition, enclosureing wild saithe have reduced levels of glucose and choline compared to control wild fish. This reproduced the variation in the metabolic tissue profile between the two groups. The authors reported that the raised AAs and lactate concentrations were due to lactic acid anaerobic fermentation as a result of inadequate O\({}_{2}\). The \({}^{1}\)H-\({}^{13}\)C-NMR was employed to control the postmortem spoilage in _S. salar_ fillets kept at 0 and 4 \({}^{\circ}\)C [116]. The NMR profile of fillet displayed metabolites, suggesting an autolytic and microbial spoilage below chilled conditions [117]. At 4 \({}^{\circ}\)C, fillets presented an earlier reduction in glycine and glutamate levels, indicating bacterial degradation. By virtue of the autolytic spoilage, His, \(\beta\)-Ala, and 1-methyl-His analyses were developed at 4 \({}^{\circ}\)C rather than at 0 \({}^{\circ}\)C. Fillets retained more trimethylamine oxide (TMAO) to trimethylamine (TMA) than samples stored at 0 \({}^{\circ}\)C. The Tyr and Lys breakdown engendered a specific intensification of malodourous tyramine and cadaverine in fillets stored at 4 \({}^{\circ}\)C [116]. Metabolomics detected TMA as a spoilage biomarker, while a reduction in glucose followed by an increase in organic acid levels signaled the microbial sugar fermentation. In this study, photobacterium, the principal bacterial genus, could convert tissue TMAO to raised TMA levels and exploit glucose as a C source to progress the spoilage throughout _S. salar_ cold storage of vacuum-packed [118]. [PERSON] et al. [119] classified raw from frozen-thawed _S. salar_ fillets. In this study, \({}^{1}\)H-NMR metabolomics differentiate these two different sample fillets.