Free Saturated Oxo Fatty Acids (SOFAs) and Ricinoleic Acid in Milk Determined by a Liquid Chromatography-High-Resolution Mass Spectrometry (LC-HRMS) Method

Abstract

Oxidized saturated fatty acids, containing a hydroxyl or an oxo functionality, have attracted little attention so far. Recent studies have shown that saturated hydroxy fatty acids, which exhibit cancer cell growth inhibition and may suppress β-cell apoptosis, are present in milk. Herein, we present the application of a liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method for the detection and quantification of various saturated oxo fatty acids (SOFAs) previously unrecognized in milk. This robust and rapid analytical method, which involves simple sample preparation and a single 10-min run, revealed the presence of families of oxostearic acids (OSAs) and oxopalmitic acids (OPAs) in milk. 8OSA, 9OSA, 7OSA, 10OSA and 10OPA were found to be the most abundant SOFAs in both cow and goat milk. Higher contents of SOFAs were found in cow milk in comparison to goat milk. Together with SOFAs, ricinoleic acid, which is isobaric to OSA, was detected and quantified in all milk samples, following a “suspect” HRMS analysis approach. This unique natural fatty acid, which is the main component (>90%) of castor oil triglycerides, was estimated at mean content values of 534.3 ± 6.0 μg/mL and 460 ± 8.1 μg/mL in cow and goat milk samples, respectively.

Identification of an Analytical Method Interference for Perfluorobutanoic Acid in Biological Samples

“…SOFAs are involved in fatty acid biosynthesis pathways in all eukaryotes, contain a carboxylic acid group for negative mode ionization, and have been documented in bacteria, 16 yeast, 17 human breath, 18 human plasma, 19 rabbit plasma, 20 and cows and goats milk. 21 Of the several potential dodecanoic SOFAs with the assigned formula C 12 H 22 O 3 , we hypothesize that 3-oxododecanoic acid (Figure 2) is the major chemical interferent observed in the placenta samples, with the interfering 213 → 169 transition occurring as a minor, secondary fragment (Figure 2). CFM-ID predictions yielded a primary fragment at 169.1598 m/z, which matches the observed interference in the 213 → 169 ion channel in the low-resolution instrument, but empirical measurements of the small concentrations of interfering precursor mass on the HRMS observed 59.0134 amu as being the major ion fragment (Supporting Information, Figure S1).…”

“…We assigned the most likely chemical class to be a saturated oxo-fatty acid (SOFA), which comprised seven of the 149 chemical structures identified in the CompTox Chemicals Dashboard search. SOFAs are involved in fatty acid biosynthesis pathways in all eukaryotes, contain a carboxylic acid group for negative mode ionization, and have been documented in bacteria, yeast, human breath, human plasma, rabbit plasma, and cows and goats milk …”

Molecular characterization of a new strain of Aspergillus and ricinoleic acid production from castor oil by the fungus

“…And the peak at m/z 180 is due to the alpha cleavage of the molecule. Due to the presence of these prominent peaks, the compound was identified to be ricinoleic acid 28,29 . The standard of ricinoleic acid (RA) (Sigma‐Aldrich) was dissolved in acetonitrile and was analyzed using the MS analyzer under the same conditions as that of the sample.…”

“…Therefore, further experiments were carried out using Isolate D. peaks, the compound was identified to be ricinoleic acid. 28,29 The standard of ricinoleic acid (RA) (Sigma-Aldrich) was dissolved in acetonitrile and was analyzed using the MS analyzer under the same conditions as that of the sample. The fragmentation pattern in the case of the standard RA (Figure 2a) matches that of the sample (Figure 2b).…”

Liquid Chromatography-Mass Spectrometry (LC-MS) Derivatization-Based Methods for the Determination of Fatty Acids in Biological Samples

“…Such uncommon (rare) FAs are usually found at low concentrations; however they exert interesting bioactivities. These uncommon FAs include odd-chain, branched and cyclic FAs [ 8 ] and FAs bearing functional groups such as hydroxy [ 9 , 10 , 11 , 12 ], oxo [ 13 , 14 ], epoxy [ 15 , 16 ] and nitro [ 17 , 18 ].…”