Polymethylene-Interrupted, Omega-3 and Branched-Chain Fatty Acids and Stable ¹³C Values of Wild Gulf of Mexico Oysters (<i>Crassostrea virginica</i>) from the Texas Coast

The complex fatty acid (FA) composition of the edible portion of American oysters (<i>Crassostrea virginica</i>) presents a significant analytical challenge to complete characterization. Here, we employed solvent-mediated covalent adduct chemical ionization to enable comprehensive <i>de novo</i> characterization of its FA composition, with isotope ratio mass spectrometry for initial measurements of FA ¹³C signatures. Unusual polymethylene-interrupted (PMI) polyunsaturates were unequivocally identified, with 22:2(7<i>Z</i>,15<i>Z</i>) dominating at 5.5% (w/w). In contrast, sea urchins collected from the same area are abundant in shorter-chain-length C20 PMI-FA. Three even-numbered-chain <i>anteiso</i> branched-chain FAs (BCFAs), C14, C16, and C18, were characterized for the first time. Gulf oysters contain 1.8% total BCFA and 23.2% combined EPA and DHA. A 100 g serving of oysters provides 32.9 mg of BCFA; 140.1 mg of PMI-FA; and 426.9 mg of EPA and DHA. Oysters and sea urchins from the same origin exhibit significantly different δ¹³C values for most measured FA, indicating distinct dietary origins.