## 7 Lipidomics and Seafood
Air-dried salmon lipidomic fingerprinting at different temperatures by machine learning (ML) methods (neural networks, support vector machines, ensemble learning, and naive bayes) was investigated by [PERSON] et al. [202]. They discovered that glycerophospholipids (GPs), glycerides (GLs), and sphingolipids, are differential expression metabolites (DEMs). The common octopus _Octopus vulgaris_ has become one of the most prized haleutic resources in the EU [203] due to its palatability and richness in omega-3 polyunsaturated fatty acids (PUFA), such as eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3). It also has a health and nutritional biochemical profile and is rich in omega-3 PUFA and other lipids [204]. Using a high-resolution mass spectrometry HILIC-LC-MS lipidomics approach, the polar lipidome of the arm muscle of _O. vulgaris_ was determined by [PERSON] et al. [205]. The main phospholipids were phosphatidylcholine and phosphatidylcholine, while the main sphingolipids identified were phosphonolipid CAEP and ceramides. Moreover, a high proportion of EPA, DHA, and several other very-long-chain fatty acids (24:5, 24:6) esterified in the polar lipid were detected. [PERSON] et al. [206] employed lipidomics and GC-ion mobility spectrometry (IMS) and investigated the correlation between flavor-active compounds and 16 differential lipids in composite surimi. They found that flavor formation was linked with triglyceride degradation and phosphatidylcholine biosynthesis. [PERSON] et al. [207] explored the changes in lipids of fish during frozen storage using lipidomics and found that differences between fresh fish and frozen fish might occur due to lipid side-chain modifications and lipid decomposition during long-term storage. [PERSON] et al. [208] employed untargeted lipidomics and ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-Q-Exactive Orbitrap mass spectrometry) along with multivariate statistics (principal component analysis (PCA)) and partial least squares-discriminate analysis (PLS-DA) to determine the lipid profiles of oyster _Crassostrea gigas_ from the Yellow Sea (YS), East China Sea, and South China Sea (SCS). The results elucidated that lipid content, composition, and lipid molecular profiles were greatly affected by geographical differences. Hence, geographical origin traceability can be based on the discrimination of lipids among marine shellfishes. An essential species in scallop farming is _Patinopecten vessoensis_. [PERSON] et al. [89] showed that 70 \({}^{\circ}\)C was the best temperature for hot air drying, and the moisture content of the scallops was less than 20% after 12 h of drying. They investigated the effect of drying on the flavor of scallops by lipidomics. They found that 2,5-dimethyl pyrazine and tetramethyl pyrazine are the characteristic flavor compounds that changed significantly during drying. In addition, taste peptides, such as Arg-Gly and Gly-Gly were found. UPLC-Q Extractive HF-X (ultrahigh-performance liquid chromatography-Q-exactive HF-X obritrap mass spectrometer) and chemometrics applied, including PCA and PLS-DA (partial least squares discriminant analysis), heatmap analysis, and cluster analysis using MetaboAnalyst 5.0, were the tools applied to analyze the lipid composition of the scallop samples. A reversed-phase liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (RPLC-Q-TOF-MS/MS) was employed by [PERSON] et al. [209] for the determination of the lipid profiles of three marine fish species, including _Pseudosciena crocca (P. crocca)_, _Sebastodes fuscens_ (_S. fuscens_), _Cololabis saira_ (_C. sain_) and one freshwater fish species _Hypophthalmichthys moltirix_ (_H. moltirix_). Comparative analysis was conducted with marine species focusing on the three anatomical parts (head, muscle, and viscera). A significant abundance of diacylglycerol(DG) was shown in the viscera of four fish species, showing their great potential as functional lipids.