## 4 An Outline of Lipidomics  
### Lipidomics and quality  
Lipidomics is responsible for the identification of key lipid biomarkers in metabolic regulation. This is achieved mainly by comparison of lipid metabolic changes under different conditions. The final aim is revealing the mechanisms of lipid action [69]. Differences in lipid-metabolizing capacity arise from different salt substitutions affecting microorganisms' activity associated with lipolytic enzymes. Hence, the overall flavor might be affected by lipid changes in meat products [70]. Moreover, there might be an accumulation of certain fat-soluble volatile flavor compounds in lipid molecules, leading to a slow release over time [71]. Lipidomics can use the identification information derived from large amounts of data for lipid identification from different sources. In this direction, gas chromatography tandem ion mobility spectrometry (GC-IMS) technology can be employed to identify and characterize compounds with ham flavor (Yang, [72]). Free fatty acids (FFAs), glycerolipids (GLs), glycerophospholipids (GPs), sphingolipids (SLs), sterol lipids, phenol lipids, saccharolipids and polyketides are considered the main lipid categories of meat [73]. Triacylglycerolgycroels (TAGs) and phospholipids (PLs) constitute two of the most common and abundant categories of lipids rich in \(\omega\)3 polyunsaturated fatty acids (PUFAs). They have health- and nutrition-related roles in the body. Lipidomics is the analytical strategy for investigation lipids in various food matrices. Fingerprinting and dynamic alterations related to lipids continue to be unexplored and are ambiguous [74; 75]. Lipidomics based on HPLC-HRMS can be employed for characterization of lipids in pork [76], duck [77] and lamb [78]. Lipid metabolism changes and their compositions for discrimination of lipid species have been detected by mass spectrometry (MS)-based lipidomics [79]. iKnife and rapid evaporative ionization mass spectrometry (REIMS)-based lipidomics have been employed by [PERSON] et al. [80] for identification of salmon and rainbow trout in real time [81]. In this direction, lipid composition changes of hams from different origins have been studied extensively [78]. Raw pork meat has been discriminated by lipidomic fingerprints [76] and the mechanism of lipid fragmentation in refrigerated Tan sheep has been well documented [82]. Many previous studies have been reported on ham lipids, focusing on the famous dry-cured pork ham produced in the Mediterranean region and China [83; 84; 85; 86; 87]. There is a significant variation in lipid composition among different raw materials [78]. [PERSON] et al. [69] used non-targeted lipidomics, correlation analysis and KEGG pathway analysis and investigated microbial and lipid metabolism changes during fermentation of restructured duck ham with different salt substitutions. Different techniques have been employed in the classification of hams based on the lipid profile. For example, gas chromatography with flame ionization detector (GC-FID) of the lipidic fraction after transmethylation in acid medium [88]. Lipid analysis of different types of food has been accomplished by proton nuclear magnetic resonance (\({}^{1}\)H NMR) spectroscopy [89; 90; 91] and analysis of the lipid profile of Iberian dry-cured hams using high-field \({}^{1}\)H NMR spectroscopy [92; 93]. Figure 4 depicts an MS-based lipidomics approach, which can be divided into: lipid extraction, lipid identification by either gas chromatography (GC)/liquid chromatography (LC)-MS and data processing with lipid classification using a chemometric approach by PCA, PLS-DA or other bioinformatics data analysis.