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

The complex fatty acid (FA) composition of the edible portion of American oysters (Crassostrea virginica) presents a significant analytical challenge to complete characterization. Here, we employed solvent-mediated covalent adduct chemical ionization to enable comprehensive de novo 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(7Z,15Z) 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 anteiso 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.