Two-Dimensional ³¹P,¹H NMR Spectroscopic Profiling of Phospholipids in Cheese and Fish

Phospholipids (PLs) comprise an important lipid class in food because of their technological use as emulsifiers and their nutritional value. This study used one-dimensional ³¹P NMR and two-dimensional (2D) ³¹P,¹H COSY NMR spectroscopy for the determination of the PL composition of cheese and fish after liquid–liquid enrichment. This extraction step enabled the identification of 10 PLs in cheese and 9 PLs in fish by 2D ³¹P,¹H NMR. Variations in the ³¹P shifts indicated differences in the fatty acids attached to the individual PLs. The total PL content in cheese fat and fish oil ranged from 0.3 to 0.4% and from 5 to 12%, respectively. Phosphatidylcholine was the most prominent PL in both matrices (up to 65%). Minor PLs (limit of detection = 4 nmol, i.e. 500 μL of an 8 μM solution) were identified in forms of phosphatidic acid, lysophosphatidic acid, and phosphatidylglycerol. Specific cross couplings and ¹H fine structures in the 2D ³¹P,¹H NMR spectra proved to be valuable for the assignment and verification of known and uncommon PLs in the samples.