Capillary electromigration methods for fatty acids determination in vegetable and marine oils: A review

Fatty acids determination is of paramount importance for quality control and suitable labeling of edible oils, required by regulatory agencies in several countries, and fast methods for this determination are worldly desired. This review article aimed to explore the available analytical methods for vegetable and marine oils analyses employing CE, which can be a straightforward and faster alternative than GC methods for fatty acid determination, considering some purposes. CE usually offers the possibility of a rapid analysis with a simple preparation of the sample, without requiring specific columns, which are inherent advantages of the technique. Instrumental conditions and the key points about fatty acids determination employing the technique are highlighted, and the main challenges and perspectives are also approached. Potential use of CE for edible oil analyses has been demonstrated for research and routine, which can be of interest for industries, regulatory agencies, and edible oil researchers. Therefore, we have explored the analytical approaches described in the last decades, intending to spread the interest of CE methods for fatty acid monitoring, label accuracy assessment, and food authenticity evaluation of edible oils.     

Analysis of free fatty acids and fatty acid phenacyl esters in vegetable oils and margarine by capillary electrochromatography

Capillary electrochromatography (CEC) has been utilized to analyze free fatty acids (FFAs) and fatty acid phenacyl esters (FAPEs) originating from vegetable oils and margarine. The analyses were performed on capillaries 25 and 40 cm long, 100 microm ID, and packed with 3 microm Hypersil ODS. Isocratic elution was achieved with the mobile phase acetonitrile/50 mM 2-(N-morpholino)ethane sulfonic acid (MES), pH 6, at a ratio of 9:1. For quantitative analysis, the formation of FAPE derivatives is preferred. Moreover, the number of double bonds in the FAPEs can be elucidated by measuring the UV absorbance ratio of 240:210 nm. For the determination of the oleate/elaidate ratio in margarines, the FFAs are analyzed because of overlap of elaidate/palmitate in FAPE analysis. Data obtained with CEC and micro liquid chromatography (LC) were compared and CEC was found to be far superior in terms of efficiency and speed of analysis. Important selectivity differences were noted between micro LC on highly endcapped ODS and CEC on the silanol-rich Hypersil ODS.     

Boronic esters as ionophores for potentiometric discrimination of the cis-trans isomeric dicarboxylic acids

Boronic esters incorporated into a poly(vinyl chloride) (PVC)-supported liquid membrane electrodes have displayed an anionic ionophore properties enabling their use in the potentiometric high-throughput screening procedures. These compounds belong to the class of ligands in which the anion recognition process can be explained on the concept of Lewis type acid-base interactions. Membranes containing boronic esters showed fairly good sensitivity for maleate (cis-isomer) in comparison to fumarate anions (trans-isomer). The potentiometric selectivity coefficients of proposed electrodes proved that common anions did not interfered with the maleate anion determination. The influence of structure of the three boronic esters ionophores on generation of potentiometric signal by developed liquid membrane electrodes was shortly discussed.     

Rapid discrimination of fatty acid composition in fats and oils by electrospray ionization mass spectrometry.

Fatty acids in 42 types of saponified vegetable and animal oils were analyzed by electrospray ionization mass spectrometry (ESI-MS) for the development of their rapid discrimination. The compositions were compared with those analyzed by gas chromatography-mass spectrometry (GC-MS), a more conventional method used in the discrimination of fats and oils. Fatty acids extracted with 2-propanol were-detected as deprotonated molecular ions ([M-H]-) in the ESI-MS spectra of the negative-ion mode. The composition obtained by ESI-MS corresponded to the data of the total ion chromatograms by GC-MS. The ESI-MS analysis discriminated the fats and oils within only one minute after starting the measurement. The detection limit for the analysis was approximately 10(-10) g as a sample amount analyzed for one minute. This result showed that the ESI-MS analysis discriminated the fats and oils much more rapidly and sensitively than the GC-MS analysis, which requires several tens of minutes and approximately 10(-9) g. Accordingly, the ESI-MS analysis was found to be suitable for a screening procedure for the discrimination of fats and oils.     

Sensitive and accurate quantitation of monoepoxy fatty acids in thermoxidized oils by gas-liquid chromatography

A sensitive and accurate methodology for quantitation of monoepoxy fatty acid methyl esters (FAME) by gas-liquid chromatography is proposed. Analytical problems of interfering compounds, ie, methyl monoester of azelaic acid and methyl docosanoate, were solved by a second methylation step with diazomethane and by elimination of nonpolar FAME by adsorption chromatography, respectively. Six monoepoxy FAME were identified and quantitated in olive and sunflower oils heated at 180 degrees C for 15 h: trans-9,10- and cis-9,10-epoxystearate coming from oleate and trans-12,13-, trans-9,10-, cis-12,13- and cis-9,10-epoxyoleate coming from linoleate. Results demonstrated total recovery of monoepoxy compounds after nonpolar FAME elimination with the additional advantage of sample concentration, which allowed quantitation of monoepoxy FAME in the initial oils. Also, repeatability was excellent as relative standard deviations ranged from 2.2 to 5.1% for on-column injection and from 0.1 to 2.0% for automatic split injection.     

Water-soluble zinc porphyrins as artificial receptors for amino acids

The binding of amino acids to water-soluble zinc porphyrins in basic aqueous solution was spectrophotometrically analyzed. The amino acids were bound to the porphyrins through the coordination of the N atom with the central zinc ion. Additional attractions arise due to Coulomb interactions between the -COO(-) anion of the amino acids and the -N(CH(3))(3)(+) cation of the porphyrin substituents and due to hydrophobic interactions between the porphyrin plane and the hydrophobic substituents of the amino acids. These attractions could be explained based on the binding data. The compensatory relationships of DeltaS and DeltaH were also discussed.     

Hollow fiber liquid-phase microextraction coupled with gas chromatography-flame ionization detection for the profiling of fatty acids in vegetable oils

The development of a two phase hollow fiber liquid-phase microextraction technique, followed by gas-chromatography-flame ionization detection (GC-FID) for the profiling of the fatty acids (FAs) (lauric, myristic, palmitic, stearic, palmitoleic, oleic, linoleic, linolenic and arachidic) in vegetable oils is described. Heptadecanoic acid methyl ester was used as the internal standard. The FAs were transesterified to their corresponding methyl esters prior to the extraction. Extraction parameters such as type of extracting solvent, temperature, extraction time, stirring speed and salt addition were studied and optimized. Recommended conditions were extraction solvent, n-tridecane; extraction time, 35 min; extraction temperature, ambient; without addition of salt. Enrichment factors varying from 37 to 115 were achieved. Calibration curves for the nine FAs were well correlated (r(2)>0.994) within the range of 10-5000 μg L(-1). The limit of detection (signal:noise, 3) was 4.73-13.21 ng L(-1). The method was successfully applied to the profiling of the FAs in palm oils (crude, olein, kernel, and carotino cooking oil) and other vegetable oils (soybean, olive, coconut, rice bran and pumpkin). The encouraging enrichments achieved offer an interesting option for the profiling of the minor and major FAs in palm and other vegetable oils.     

High performance liquid chromatography determination of fatty acids in drying oils following lipase action

This paper describes a quantitative analytical procedure to determine the fatty acid composition in drying oils like linseed, walnut and poppy seed. The procedure required the enzymatic hydrolysis of the oil triacylglycerol families by the action of Candida rugosa lipase. The fatty acids (FFAs) produced (linolenic, myristic, linoleic, palmitic, oleic and stearic) were extracted with n-heptane and derivatized with α-bromoacetophenone. Their separation and quantitative determination were performed by high-performance liquid chromatography employing a C18 column and an isocratic elution method coupled to ultraviolet detection. The analytical enzymatic procedure is sensitive for < 0.5 μg/mL of FFAs in a reduced sample of 0.1 mg of drying oil.     

Chiral discrimination of alpha-amino acids by the DNA triplet GCA using amino acids as a co-selector

The DNA triplet GCA is successfully used as a chiral selector for the chiral discrimination of amino acids using amino acids themselves as a co-selector. Chiral discrimination was achieved by investigating the collision-induced dissociation spectra of the [X(A) + X(R) + 2Y - 2H](2-) ion generated by electrospraying a mixture of analyte amino acid (X(A)), reference amino acid (X(R)) and GCA (Y). The relative abundances of fragment ions resulting from the competitive loss of reference and X(A)'s are considered for measuring the degree of chiral discrimination. GCA successfully shows D-selectivity for all the amino acids, except Tyr and Lys. The success of the method lies in the selection of a suitable 10(R) that has closer GCA binding affinity to that of analyte. The degree of discrimination by GCA is improved in the presence of the reference, and the chirality of the reference does not change the selectivity of GCA. The suitability of the method for the measurement of optical purity is also demonstrated.     

Cyclopropyl containing fatty acids as mechanistic probes for cytochromes P450

[reaction: see text] The mechanism of aliphatic hydroxylation by cytochromes P450 has been the subject of intense debate with several proposed mechanistic alternatives. Various cyclopropyl containing compounds (radical clocks), which can produce both unrearranged and ring opened products upon oxidation, have been key tools in these investigations. In this study, we introduce several cyclopropyl containing fatty acids 1a-4a with which to probe the mechanism of P450s capable of fatty acid hydroxylation. The probes are shown to be capable of distinguishing radical from cationic intermediates due to the rapid equilibration of isomeric cyclopropyl cations. Ring opening of a radical intermediate in an oxidative transformation is expected to yield a single rearranged alcohol, whereas a cation isomerizes prior to ring opening, leading to two isomeric homoallylic alcohols. Oxidation of these probes by P450(BM3) and P450(BioI) gives results consistent with a radical but not a cationic intermediate in fatty acid hydroxylation by these enzymes. Quantitation of the unrearranged and ring opened products gives remarkably homogeneous rates for oxygen rebound of (2-3) x 10(10) s(-1). The effects of introduction of a cyclopropane ring into a fatty acid upon the regiochemistry of hydroxylation are discussed.     

An investigation of frequently consumed edible oils in Turkey in terms of omega fatty acids

The fatty acid profiles of frequently consumed oils and crops cultivated in Turkey were investigated in regard to omega fatty acids. Analyses were carried out on commercially sold oils, sunflower, olive, and fish oils, and oils extracted from fatty seeds of hazelnut, walnut, olive, sunflower, poppy, sesame, and pumpkin, and butter produced in Turkey. Hazelnut and olive oils were found to be rich in omega-9 (oleic acid 18:1), walnut, poppy seed, sesame, and pumpkin seed were rich in omega-6 (linoleic acid 18:2), and butter was rich in short chain fatty acids and omega-9. Fish oil, from mackerel, was the richest in omega-3 fatty acids and fatty acid diversity. There were some alterations between commercially sold oils and oils extracted from seeds in regard to fatty acid percentages and variety.     

Hydropyrolysis as a preparative method for the compound-specific carbon isotope analysis of fatty acids

Compound-specific stable carbon isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry is an effective and risk-free means of investigating fatty acid metabolism. Straightforward analysis, however, leads to poor chromatographic resolution, while derivatization adds carbon thereby corrupting the starting stable isotopic composition. Hydropyrolysis is a new approach which defunctionalizes fatty acids to yield the corresponding n-alkanes thus retaining the carbon skeleton intact and improving chromatography, allowing the faithful measurement of carbon isotope ratios.     

Serum metabolomics reveals the deregulation of fatty acids metabolism in hepatocellular carcinoma and chronic liver diseases

Patients with chronic liver diseases (CLD) including chronic hepatitis B and hepatic cirrhosis (CIR) are the major high-risk population of hepatocellular carcinoma (HCC). The differential diagnosis between CLD and HCC is a challenge. This work aims to study the related metabolic deregulations in HCC and CLD to promote the discovery of the differential metabolites for distinguishing the different liver diseases. Serum metabolic profiling analysis from patients with CLD and HCC was performed using a liquid chromatography–mass spectrometry system. The acquired large amount of metabolic information was processed with the random forest–recursive feature elimination method to discover important metabolic changes. It was found that long-chain acylcarnitines accumulated, whereas free carnitine, medium and short-chain acylcarnitines decreased with the severity of the non-malignant liver diseases, accompanied with corresponding alterations of enzyme activities. However, the general changing extent was smaller in HCC than in CIR, possibly due to the special energy-consumption mechanism of tumor cells. These observations may help to understand the mechanism of HCC occurrence and progression on the metabolic level and provide information for the identification of early and differential metabolic markers for HCC.     

超高效合相色谱-质谱法快速分析食用植物油中常见脂肪酸

建立了超高效合相色谱-质谱(UPC²-MS)快速分析6种食用植物油(玉米油、葵花籽油、大豆油、茶油、菜籽油、花生油)中棕榈酸、硬脂酸、油酸、亚油酸、亚麻酸等5种常见脂肪酸的方法,并比较了这6种食用油中上述5种脂肪酸的含量差异。采用皂化反应对植物油进行前处理,以ACQUITY UPC² BEH 2-EP色谱柱(100 mm×2.1 mm, 1.7 μm)为分析柱,以超临界CO₂-甲醇/乙腈(1:1, v/v)为流动相进行梯度洗脱,流速为0.8 mL/min。在电喷雾负离子模式下进行检测,外标法定量。结果表明:5种脂肪酸标准物质在0.5~100 mg/L范围内呈现良好的线性关系,相关系数为0.9985~0.9998,定量限(S/N≥10)为0.15~0.50 mg/L;在3个添加水平下,样品的加标回收率为89.61%~108.50%;方法重复性的相对标准偏差(RSD)为0.69%~3.01%。该方法简单、快速、分离效果好,无需对脂肪酸样品进行衍生化,已成功地用于玉米油、葵花籽油、橄榄油、茶油、大豆油和花生油等6种食用油中常见脂肪酸含量的测定。     

Profiling fatty acids in vegetable oils by reactive pyrolysis-gas chromatography with dimethyl carbonate and titanium silicate

A novel methodology in on-line pyrolysis-gas chromatography (Py-GC) for the fast analysis of fatty acids in vegetable oils with minimal sample treatment and the use of non-toxic reagents is described. Pyrolysis at 500 degrees C for 10 s of sub-microgram quantity of vegetable oil dissolved in dimethyl carbonate (DMC) and in the presence of nanopowder titanium silicon oxide resulted in the production of fatty acid methyl esters (FAMEs) as unique products. Pyrolysis performed by means of a resistively heated filament pyrolyser interfaced to a GC-MS apparatus enabled the direct analysis of evolved FAMEs. The DMC/Py-GC-MS analysis was tested on soybean, coconut, linseed, walnut and olive oil and the results compared to the classical BF(3)-methanol as reference methodology. The DMC method exhibited a lower precision and was biased towards lower levels of polyunsaturated fatty acids (PUFA) in comparison to the BF(3)-methanol method, but was more advantageous in terms of reduced sample treatment, waste generation and risk factors of employed chemicals.     

Essential and fatty oils of Agastache rugosa

Northern Caucasus Zonal Experimental Station of VILR [All-Union Scientific Research Institute of Medicinal and Aromatic Plants], Vasyurinskaya, Krasnodar Territory. Translated from Khimiya Prirodnykh Soedinenii. No. 3, pp. 449–450, May–June, 1988.     

Characterisation of fatty acids in drying oils used in paintings on canvas by GC and GC-MS analysis

Of the various binding media used in paintings, this work examines drying oils. During the initial phase of polymerisation and the progressive ageing process, the fraction of unsaturated and polyunsaturated fatty acids undergoes various changes (reticulation, oxidation, etc.), that give rise to characteristic compounds. Within a broader research project, aimed at the characterisation of binding media, a preliminary study was made of the ageing process of linseed oil. In this regard, linseed oil was spread on a glass or canvas support and then dried in the open air. The ageing of the spread linseed oil was monitored by taking samples of the material at regular intervals. After the fatty acids had changed into methylesters, the samples were analysed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The results obtained have been reported as a ratio between the areas of the chromatographic peaks of the different fatty acids found.