Direct 1H NMR Quantitation of Valuable Furan Fatty Acids in Fish Oils and Fish Oil Fractions

NMR Analysis of Extra Virgin Olive Oil of the Epirus Region of Greece with Emphasis on Selected Phenolic Compounds

Extra virgin olive oil (EVOO) is recognized for its numerous health benefits, attributed to its rich phenolic components. NMR has emerged as a prevalent technique for precisely identifying these compounds. Among Mediterranean countries, Greece stands as the third-largest producer of olives, with the Epirus region notably advancing in olive cultivation, contributing significantly to the dynamic growth of the region. In this study, an NMR method was employed based on the acquisition of a 1H NMR spectrum along with multiple resonant suppression in order to increase the sensitivity. Using the above method, 198 samples of extra virgin olive oil, primarily sourced from the Epirus region, were analyzed, and both the qualitative and quantitative aspects of the phenolic compounds were obtained. In addition, we examined the effects of various factors such as variety, harvest month, and region origin on the phenolic compounds' concentration. The results revealed an average total phenolic content of 246 mg/kg, closely approaching the EU health claim limit of 250 mg/kg. Approximately 15% of the samples were confidently characterized as high-phenolic olive oil. The highest concentrations were observed in the Thesprotia samples, with several Lianolia varieties exceeding the total phenolic content of 400 mg/kg. Statistical tests demonstrated a significant influence of the olive variety and the month of fruit harvest on phenolic component concentration, followed by the region of origin. A very strong correlation was noted between the total phenolics content and the levels of oleocanthal and oleacein, with a correlation coefficient (r) of 0.924. Upon optimization of all factors affecting olive oil quality, the majority of the EVOOs from the Epirus region have the potential to be characterized as high in phenolic content.

Geometrical and positional isomers of unsaturated furan fatty acids in food

Furan fatty acids (FuFA) are important antioxidants found in low concentrations in many types of food. In addition to conventional FuFA which normally feature saturated carboxyalkyl and alkyl chains, a few previous studies indicated the FuFA co-occurrence of low shares of unsaturated furan fatty acids (uFuFA). For their detailed analysis, the potential uFuFA were enriched by centrifugal partition chromatography (CPC) or countercurrent chromatography (CCC) followed by silver ion chromatography from a 4,7,10,13,16,19-docosahexaenoic acid ethyl ester oil, a 5,8,11,14,17-eicosapentaenoic acid ethyl ester oil and a latex glove extract. Subsequent gas chromatography with mass spectrometry (GC/MS) analysis enabled the detection of 16 individual uFuFA isomers with a double bond in conjugation with the central furan moiety. In either case, four instead of two uFuFA isomers previously reported in food, respectively, were detected by GC/MS. These isomers showed characteristic elution and abundance patterns in GC/MS chromatograms which indicated the presence of two pairs of cis/trans-isomers (geometrical isomers).

Furan Fatty Acids in Some 20 Fungi Species: Unique Profiles and Quantities

Furan fatty acids (FuFAs) are a group of excellent antioxidants in food. Since data in fungi were scarce, 37 commercial or collected edible and meadow fungi were analyzed on FuFA patterns and contents. FuFA amounts in fresh fungi ranged from not detectable (n = 2) to 40 mg/100 g fungi dry weight. Fresh samples of the popular edible fungi genera Agaricus and Pleurotus showed comparable FuFA contents of 9.0-33 mg/100 g fungi dry weight. The unique FuFA profile of the fungi was dominated by 9-(3,4-dimethyl-5-pentylfuran-2-yl)-nonanoic acid (9D5). In addition, the uncommon 9-(3,4-dimethyl-5-butylfuran-2-yl)-nonanoic acid (9D4) was present in 30% of the samples with contents of up to 0.2 mg/100 g fungi dry weight. Countercurrent separation techniques were used to isolate the main FuFA 9D5, to verify the presence of 9D4, and to determine ultra-traces of 11-(3,4-dimethyl-5-pentylfuran-2-yl)-undecanoic acid (11D5), which may have been assimilated by the fungi from the substrate.

Valuable furan fatty acids in soybeans and soy products

Furan fatty acids (FuFAs) are valuable minor compounds in our food with excellent antioxidant properties. Naturally occurring FuFAs are characterised by a central furan moiety with one or two methyl groups in β-/β’-position of the heterocycle (monomethyl- or M-FuFAs and dimethyl- or D-FuFAs). Comparably high concentrations of D-/M-FuFAs were reported in soybeans, but soy is often consumed as a processed product, such as full-fat soy flour and flakes, soy drink, tofu and texturised soy protein (TSP). Due to the chemical lability of D-/M-FuFAs, e.g. in the presence of light or oxygen, a degradation during the processing is possible. For this purpose, freshly harvested soybeans (n = 4) and differently processed soybean products (n = 22) were analysed on FuFAs. Three FuFAs, i.e. 11-(3,4-dimethyl-5-pentylfuran-2-yl)-undecanoic acid (11D5), 9-(3,4-dimethyl-5-pentylfuran-2-yl)-nonanoic acid (9D5), and 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid (9M5), were identified and quantified in all fresh soybeans and most of the processed soy products (n = 20). A trend towards lower D-/M-FuFA contents in higher processed products was observable. Lower FuFA concentrations were usually accompanied with a decrease of the share of the less stable D-FuFAs (9D5, 11D5) in favour of the M-FuFA 9M5. Furthermore, one or two 3,4-nonmethylated furan fatty acids (N-FuFAs), i.e. 8-(5-hexylfuran-2-yl)-octanoic acid (8F6) and partly 7-(5-heptylfuran-2-yl)-heptanoic acid (7F7), were detected in all processed products, but not in the freshly harvested soybeans. Our results indicate that D-/M-/N-FuFAs may serve as suitable markers for both, careful manufacturing processes and adequate storage conditions of soy products.

Development of a sensitive and quantitative method for the identification of two major furan fatty acids in human plasma

This article focuses on the establishment of an accurate and sensitive quantitation method for the analysis of furan fatty acids. In particular, the sensitivity of GC/MS and UPLC/ESI/MS/MS was compared for the identification and quantification of furan fatty acids. Different methylation methods were tested with respect to GC/MS analysis. Special attention needs to be paid to the methylation of furan fatty acids, as acidic catalysts might lead to the degradation of the furan ring. GC/MS analysis in full-scan mode demonstrated that the limit of quantitation was 10 μM. UPLC/ESI/MS/MS in multiple reaction monitoring mode displayed a higher detection sensitivity than GC/MS. Moreover, the identification of furan fatty acids with charge-reversal derivatization was tested in the positive mode with two widely used pyridinium salts. Significant oxidation was unexpectedly observed using N-(4-aminomethylphenyl) pyridinium as a derivatization agent. The formed 3-acyl-oxymethyl-1-methylpyridinium iodide derivatized by 2-bromo-1-methylpyridinium iodide and 3-carbinol-1-methylpyridinium iodide improved the sensitivity more than 2,000-fold compared with nonderivatization in the negative mode by UPLC/ESI/MS/MS. This charge-reversal derivatization enabled the targeted quantitation of furan fatty acids in human plasma. Thus, it is anticipated that this protocol could greatly contribute to the clarification of pathological mechanisms related to furan fatty acids and their metabolites.