Concentrations of medium-chain 2- and 3-hydroxy fatty acids in foodstuffs

Medium chain 2-hydroxy fatty acids and 3-hydroxy fatty acids (2-OH-FAs and 3-OH-FAs with 8–20 carbons) are widespread in nature but little was known about the quantities of these minor fatty acids in food. For this reason, the concentrations and composition of 2- and 3-OH-FAs in several foodstuffs (milk and dairy products, animal brains, suet, vegetable oils) and two non-food samples (wool wax and vernix caseosa) were determined by gas chromatography with electron-capture negative ion mass spectrometry in the selected ion monitoring mode. Lipids were isolated from samples by accelerated solvent extraction. After transesterification the obtained fatty acid methyl esters (FAMEs) were separated into OH-FAMEs and non-OH-FAMEs. The OH-FAMEs were converted into pentafluorobenzoyl (PFBO) derivatives (PFBO-O-FAMEs). 2- and 3-OH-FAs were detected in all samples analysed. Chain-length ranged from 8–20 carbons. In general, 3-OH-FAs dominated in milk and dairy products (maximum concentration 17.7 mg/100 g l.w. in goat milk) whereas 2-OH-FAs were more abundant in animal brains and suet. The lowest concentrations were determined in vegetable oils (0.21–2.42 mg/100 g l.w.) whereas the highest concentrations of 2-OH-FAs were determined in wool wax (1180 mg/100 g l.w.) and vernix caseosa (34.5 mg/100 g l.w.). -FA pattern was varied and use of specific OH-FAs was proposed as tracers for authenticity controls. Based on the concentrations determined, it was estimated that the daily uptake of OH-FAs via food is in the milligram range.