Associate Professor Sun Yat-sen University Shenzhen, Guangdong, China (People's Republic)
Abstract: Unusual seafood, such as spoon worms (Urechis unicinctus) and peanut worms (Sipunculus nudus), serve as both delicacies and potential solutions to the global food insecurity crisis. However, their nutritional compositions including fatty acid profiles were poorly characterized and quantified, due to the existence of unusual polyunsaturated fatty acid (PUFA) isomers, some of which only differ in one double bond position. To address this obstacle, we employed covalent adduct chemical ionization (CACI) tandem mass spectrometry (MS/MS) for the de novo identification and quantification of unusual PUFA. CACI is one of the advanced MS methods that derivatizes a double bond in an unsaturated lipid via an inline mode, with the Paternò–Büchi (PB) reaction and ozone-induced dissociation (OzID) being the most well-known techniques. Leveraging CACI-MS/MS, we identified several PUFA with polymethylene-interrupted (PMI) double bond configurations, including 22:3(7Z,13Z,16Z), a novel PUFA derived from sciadonic acid (20:3(5Z,11Z,14Z)). 22:3(7Z,13Z,16Z) exhibits a fragmentation pattern similar to that of 20:3(5Z,11Z,14Z), featuring an ω diagnostic ion at m/z 246, which pinpoints the Δ7 double bond position. Coeluted PMI fatty acid methyl esters differing in one double bond position have been successfully quantified by exploiting their distinctive diagnostic ions in MRM mode, without the need of authentic standards for calibration. U. unicinctus has an exceptionally low n-6/n-3 PUFA ratio of 0.15, suggesting its potential as a medicinal food to counterbalance the n-6/n-3 imbalance in modern diets. Additionally, S. nudus boasts notably high concentrations (~3%, wt/wt) of branched chain fatty acids (BCFA), exceeding typical levels found in dairy products (~2%, wt/wt).
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