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.
Highlights
Milk fat is one of the most complex natural fats because of the presence of more than 400 different fatty acids (FAs) [1,2,3]
The presence of 2-hydroxy and 3-hydroxy FAs in milk and dairy products was reported more than 10 years ago [5,6], only one report demonstrated the existence of two other saturated hydroxy fatty acids (SHFAs), 10-hydroxystearic acid and 8-hydroxypalmitic acid, in milk [7]. This year, we reported the identification in milk of new families of previously unrecognized SHFAs, namely hydroxystearic acids (HSAs) and hydroxypalmitic acids (HPAs), which exhibit cell growth inhibitory activity and the ability to inhibit cytokine-induced β-cell apoptosis [8]
By applying an liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method, which involves mild sample preparation conditions, avoiding time-consuming extraction, pre-separation or derivatization procedures, 13 free saturated oxo fatty acids (SOFAs) were simultaneously identified and quantified in cow and goat milk samples. This robust method permitted the rapid analysis of milk samples, uncovering the existence of various regioisomers of oxostearic acids (OSAs) and oxopalmitic acids (OPAs) carrying the oxo functionality at different positions of the long chain
Summary
Milk fat is one of the most complex natural fats because of the presence of more than 400 different fatty acids (FAs) [1,2,3]. These FAs vary in carbon chain length 26 carbons), including FAs with either an even or an odd number of carbon atoms, in a straight or a branched chain. They vary in the degree of unsaturation, including geometrical isomers, with double bonds in mainly cis and in trans configuration. The available data reported on the occurrence of saturated hydroxy fatty acids (SHFAs) and saturated oxo (keto) fatty acids (SOFAs) in milk are scarce
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