Master of Science University of Hohenheim, Germany
Abstract: Furan fatty acids (FuFAs) are minor heterocyclic fatty acids which are valued due to their antioxidative effects on vulnerable polyunsaturated fatty acids (PUFAs). Although their presence in a wide range of food samples has been documented in various studies, these minor fatty acids (usually < < 1% of the total fatty acids) had not been reported in lipidomics studies on triacylglycerols (TAGs).
Methods: We enzymatically synthesized FuFA-containing TAGs and studied first and second dimension LC-Orbitrap-HRMS spectra and developed protocols for their detection in food samples.
Results: FuFA-containing TAGs co-eluted with conventional TAGs. The most prominent FuFAs are norminally isobaric with conventional fatty acids but the required resolution of Dm = 0.0364 Da (type A: CH4 in a conventional fatty acid substituted with O in a FuFA) or Dm = 0.0575 Da (type B: C2 substituted with H8O) is easy met by LC-Orbitrap-HRMS instruments. However, LC-Orbitrap-HRMS filtering of the exact masses of [M+H]+ of FuFA-containing TAGs (mass accuracy better than 4 ppm) was unsuccessful. Also, screening LC-MS2 spectra of TAGs for [M-RCOO]+ fragment ions remained unequivocal. Yet, filtering [M+H]+ together with the unique base peak of FuFA-containing TAGs (formally [FuFA – OR]+) and further diagnostic fragment ions in the LC-MS2 spectra enabled the detection of >30 FuFA-containing TAGs in fish oil and mushroom samples, but a sufficient LC separation was required.
Conclusion: Using the filtering protocol developed in this study, FuFA-containing TAGs can be directly explored in extracted lipids of food and biological samples. The observed filter problems observed with LC-Orbitrap-HRMS in case of an insufficient chromatographic separation will most likely also be valid for other trace compounds.