Furan fatty acids (F-acids) are valuable bioactive compounds found at low concentrations in food. A method for the quantitative determination of saturated F-acids in food is reported. The sample preparation is based on accelerated solvent extraction, transesterification into methyl esters and silver ion chromatography (20% AgNO 3 in silica, 1% deactivated) of the resulting methyl esters. There then follows determination of the enriched F-acid methyl (or ethyl) esters by GC/EI-MS in the selected ion monitoring (SIM) mode. The 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid ethyl ester (9M5-EE) was used as an internal standard for recovery checks. The limit of detection was 11 pg, and the recovery rate of the silver ion chromatography was 85% (n = 5). Further F-acid standards were used for evaluation of individual SIM-responses. Application of the method to various biological samples gave the following results: champignons (n = 2) contained 1.7 or 2.5 mg/100 g dry weight F-acids, while fish oil capsules (n = 5) contained between 18 and 234 mg/100 g oil F-acids distributed over up to seven F-acids. The concentrations and patterns were different to fresh fish. Accordingly, fish oil supplements seem to be a minor source for F-acids compared to (fresh) fish. Organic butter samples (n = 4) contained about twice the amount of F-acids when compared with conventional butter (n = 5).

Furan fatty acids (F-acids) are valuable antioxidants containing a furan moiety in the central part of the molecule. They occur in the lipids of different foodstuffs and plants, with grass being the main source for their presence in milk fat and butter. Because cows from organic farming receive higher portions of grass-based feed, it was tested whether organic butter samples (n = 26) contain more F-acids than conventional ones (n = 25) in Germany. For this purpose, samples were melted, and the lipid phase was separated and transesterified into methyl esters, which were enriched using silver ion chromatography and analyzed by GC-EI/MS in the selected ion monitoring (SIM) mode. Levels of F-acids in butter were higher in summer than in winter, and in both seasons, organic samples contained significantly higher levels of F-acids than conventional ones (one-way ANOVA: p < 0.001). Furthermore, the daily intake of F-acids via milk fat and other foodstuffs was calculated.

Furan fatty acids (F‐acids) are heterocyclic lipid components with a furan moiety in the centre of the molecule. Reports on F‐acids in the literature are rather scarce, although they are considered as particularly valuable food ingredients. F‐acids occur as minor compounds in the lipids of different food samples. Despite the low concentrations, some studies produced evidence that the F‐acids are excellent radical scavengers and thus are able to protect polyunsaturated fatty acids from lipid peroxidation. Accordingly, they may play a currently underrated and largely overlooked positive role in human nutrition. The limited data available result from difficulties in the analysis of these trace compounds. F‐acids in food can hardly be determined without selective enrichment and the use of gas chromatography with mass spectrometry for their determination. The lack of reference standards is a further drawback that hampers the exact assessment of the actual relevance of F‐acids in human nutrition.

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Furan fatty acids (F-acids) are valuable, bioactive minor components in lipids which are characterized by a furan moiety in the acyl chain. Here, we present a gas chromatography/mass spectrometry method operated in the selected ion monitoring mode (GC/MS-SIM) for the thorough determination of F-acid as methyl esters in fish. The method takes advantage of the molecular ion and two characteristic fragment ions and enables the unequivocal detection of >350 saturated, mono-and dienoic F-acids in four GC/MS-SIM runs. This method was applied to the analysis of the methyl esters obtained from the triacylglyceride (TG) and the cholesteryl ester (CE) fraction of ten individual fish liver samples. Up to 23 Facids, including several new or scarcely detected homologues, were detected in the samples. The concentrations of total Facids ranged from 25 to 280 mg/100 g lipids in the TG fractions and <0.11 to 115 mg/100 g lipids in the CE fractions.

Furan fatty acids (F-acids) are a class of natural antioxidants with a furan moiety in the acyl chain. These minor fatty acids have been reported to occur with high proportions in the cholesteryl ester fraction of fish livers. Here we present a method for the direct analysis of intact cholesteryl esters with F-acids and other fatty acids in cod liver lipids. For this purpose, the cholesteryl ester fraction was isolated by solid phase extraction (SPE) and subsequently analyzed by gas chromatography with mass spectrometry (GC/MS) using a cool-on-column inlet. Pentadecanoic acid esterified with cholesterol was used as an internal standard. GC/MS spectra of F-acid cholesteryl esters featured the molecular ion along with characteristic fragment ions for both the cholesterol and the F-acid moiety. All investigated cod liver samples (n = 8) showed cholesteryl esters of F-acids and, to a lower degree, of conventional fatty acids. By means of GC/MS-SIM up to ten F-acid cholesteryl esters could be determined in the samples. The concentrations of cholesteryl esters with conventional fatty acids amounted to 78-140 mg/100 g lipids (mean 97 mg/100 g lipids), while F-acid cholesteryl esters were present at 47-270 mg/100 g lipids (mean 130 mg/100 g lipids).

Furan fatty acids are valuable and bioactive minor fatty acids that usually contribute <0.1% to the fatty acid content of food samples. Their biological role still remains unclear as authentic furan fatty acid standards are not readily available and thorough experimental studies verifying the relevance of furan fatty acids are thus virtually impossible. An efficient protocol for the isolation of the furan fatty acid 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid from hydrolyzed and centrifuged latex of Hevea brasiliensis was developed using countercurrent chromatography. A first run using pH-zone-refining countercurrent chromatography provided 48.4 mg of 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid from 210 mg latex extract in a purity of 95%. The purity was increased to 99% by means of one second run in conventional countercurrent chromatography mode. The Structure and purity of 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid were determined by gas chromatography coupled to mass spectrometry and (1)H and (13)C NMR spectroscopy.

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