Overview of methods for the determination of trans fatty acids by gas chromatography, silver-ion thin-layer chromatography, silver-ion liquid chromatography, and gas chromatography/mass spectrometry

trans Isomers of naturally occurring cis-unsaturated fatty acids are produced when liquid vegetable oils or marine oils are partially hydrogenated to produce margarine, shortenings, and other hardened-fat products. Isomeric trans fatty acids are also formed in the intestinal tract of ruminants, and they appear in small amounts in dairy products and ruminant meat. Currently, satisfactory analyses for the fatty acid profiles of fats containing trans fatty acids are obtained by gas chromatography (GC) using capillary columns coated with highly polar cyanosilicone stationary phases. In capillary GC methods, the key limitation has been the incomplete separation of trans-monoenoic acid isomers from their cis isomers; however, recent reports have demonstrated that improvements in separation are attainable with the use of 100 m columns. In these columns, there is very little overlap of cis and trans isomers. More accurate trans fatty acid analyses can be obtained by coupling GC with either silver-nitrate thin-layer chromatography or silver-nitrate liquid chromatography.     

深海鱼油中脂肪酸的分析

用氢氧化四甲胺／甲醇酯化法使深海鱼油内的三酸甘油酯中的脂肪酸和游离脂肪酸转化成脂肪酸甲酯,用气相色谱和气相色谱／质谱进行分析,鉴定出４１个组分,并对其中的主要组分顺式－５,８,１１,１４,１７－十二碳五稀酸（ＥＰＡ）和顺式－４,７,１０,１３,１６,１９－二十二碳六烯酸（ＤＨＡ）建立了定量分析方法。方法的相对标准偏差分别为４．３％（ＥＰＡ）和４．７％（ＤＨＡ）。ＥＰＡ和ＤＨＡ的回收率分别为１００．     

Quantification of eicosapentaenoic and docosahexaenoic acid geometrical isomers formed during fish oil deodorization by gas-liquid chromatography

Long-chain polyunsaturated fatty acids (LC-PUFAs) of the n-3 series and especially eicosapentaenoic and docosahexaenoic acids (EPA and DHA, respectively) have important biological properties. The main dietary sources of LC-PUFAs are fish and fish oil. Geometrical isomerization is one of the main reactions happening during the thermal treatment of polyunsaturated fatty acids. Refined fish oils are used to supplement food products in LC-PUFAs and the quality of these nutritional ingredients have to be controlled. In the present study, a suitable method for the quantification of EPA and DHA geometrical isomers in fish oils by gas-liquid chromatography (GC) is presented. A highly polar capillary column (CP-Sil 88, 100 m) operating under optimal conditions was used. Method selectivity was studied by GC-mass spectrometry. The performance characteristics of the quantification method were studied using samples of fish oil deodorized at 220 degrees C for 3 h. The linearity of the method was assessed by analyzing composite samples obtained by mixing fish oil deodorized at 220 degrees C with semi-refined fish oil (control). Precision was evaluated by analyzing the same samples in triplicate. Results showed that the validated method is suitable to quantify low amounts of geometrical (trans) isomers of EPA and DHA in refined fish oils. The limits of quantification of the EPA and DHA geometrical isomers are 0.16 and 0.56 g/100 g of fish oil, for EPA and DHA, respectively. Commercially available LC-PUFA oil samples were evaluated by using the validated method. The results show that the oils analyzed contain low amounts (<1% of total fatty acids) of geometrical isomers of EPA and DHA.     

Isolation and structural analysis of the cyclic fatty acid monomers formed from eicosapentaenoic and docosahexaenoic acids during fish oil deodorization

Long-chain polyunsaturated fatty acids (LC-PUFAs) present in fish oils are thermolabile molecules. Among the degradation reactions encountered, thermal cyclization occurs during refining or other heat treatments. Numerous studies have been carried out in the past to quantify and determine the structures of cyclic fatty acid monomers (CFAMs) formed from oleic, linoleic and linolenic acids in heated vegetable oils. Recently, much attention have been given to LC-PUFAs due to their potential health benefits. However, data on quantification of CFAMs formed from these fatty acids, such as eicosapentaenoic acid (EPA, cis-5, cis-8, cis-11, cis-14, cis-17 20:5) and docosahexaenoic acid (DHA, cis-4, cis-7, cis-10, cis-13, cis-16, cis-19 22:6), the two main LC-PUFAs in fish oils, are scarce. In the present study, structural analyses of CFAMs formed from EPA and DHA during the deodorization of fish oil are presented. Fish oil sample was deodorized at 250 degrees C for 3 h under a pressure of 1.5 mbar in a laboratory deodorizer. The CFAMs formed during heat treatment of fish oil were isolated by a combination of saponification, esterification, urea fractionations and column chromatography. Structural analyses of C20- and C22-CFAMs were achieved by gas-chromatography electronic-ionization mass-spectrometry (GC-EI-MS) of their 4,4-dimethyloxazoline (DMOX) derivatives. We identified seven out of 13 possible structures of hydrogenated CFAMs formed from EPA, and nine out of 16 possible structures of CFAM formed from DHA. Major CFAMs from both EPA and DHA were cyclohexyl isomers. All possible cyclohexyl isomers were found but only nine out of 18 of the cyclopentyl isomers were present in concentration sufficient for identification. Chemical mechanisms involved in the formation of polyunsaturated LC-PUFAs have been investigated. The results have shown that general principle involved in the cyclization of LC-PUFAs is same as that for the thermal cyclization of oleic, linoleic and alpha-linolenic acids.     

全二维气相色谱-四极杆质谱法检测植物油脂中脂肪酸

建立了植物油脂中31种脂肪酸成分的全二维气相色谱-四极杆质谱(GC×GC-qMS)分析方法。样品经甲酯化衍生后,以DB-1柱(30 m×0.25 mm×0.25 μm)作为一维柱、DB-Wax柱(3.2 m×0.1 mm×0.1 μm)作为二维柱组成柱系统进行分离,在调制周期为3.5 s、四极杆质量扫描范围为m/z 40～350的条件下,植物油脂中31种脂肪酸成分可以在50 min内得到准确和灵敏的检测。将本方法应用于实际样品的分析,灵敏度较传统的气相色谱-质谱法提高了100倍以上,一些植物油中微量的脂肪酸成分也因此被检出。该研究不仅为植物油中脂肪酸成分的分析提供了新的技术手段,同时对于确保食用植物油的质量安全、消除食用植物油的掺假伪劣等均有重要意义。     

New Syntheses with Oils and Fats as Renewable Raw Materials for the Chemical Industry

Oils and fats are the most important renewable raw materials for the chemical industry. Hitherto, industrial oleochemistry has concentrated predominantly on the carboxy functionality of fatty acids but, more recently, modern synthetic methods have been applied extensively to fatty compounds for the selective functionalization of the alkyl chain. Radical, electrophilic, nucleophilic, and pericyclic as well as transition metal catalyzed additions to the C-C double bond of, for example, oleic acid as the prototype of a readily accessible, unsaturated fatty acid have led to a large number of novel fatty compounds from which interesting properties are expected. Functionalization of C-H bonds in the alkyl chain is also feasible with remarkable selectivity. Effective and highly versatile catalysts for the metathesis of esters of unsaturated fatty acids have been developed, which lead to new and interesting omega-unsaturated fatty acids. The epoxidation of unsaturated fatty acids has been developed extensively. Enzymatic reactions allow syntheses with high selectivity and yield of mono- and diglycerides and esters of carbohydrates with a variety of surfactant properties. Regio- and enantioselective microbial hydrations and hydroxylations widen the spectrum of selective reactions. Of considerable significance is that, with the use of gene technology, natural oils and fats have been improved significantly and will be improved still further, insofar as they show a more uniform and often unusual fatty acid spectrum. Numerous fatty acids are now available in a purity which makes them attractive for synthesis and as raw materials for the chemical industry.     

Fast analysis by gas-liquid chromatography. Perspective on the resolution of complex fatty acid compositions

Separation of fatty acids as methyl ester (FAME) derivatives has been carried out using short and highly polar capillary column developed for fast gas-liquid chromatography (GLC) applications. The GLC parameters have been optimized in order to achieve separation of FAME ranging from 4:0 (butyric acid) to 24:1 in less than 5 min. Milk fat that has by far the most complex fatty acid composition among edible fats and oils has been used to optimize the method. The volume of the oven has been reduced in order to allow for a heating rate of 120 degrees C/min and to rapidly cool-down to the initial temperature (50 degrees C) of the GLC program. The GLC conditions developed are not suitable to achieve separation of positional and geometrical isomers of octadecenoic acid but are useful to perform separation of major fatty acids in milk fat. The conditions developed could be used to analyze edible fats and oils or biological samples such as plasma or red blood cell lipids. The results confirmed that short and highly polar fast columns operating under optimal conditions could be used to separate the fatty acids in various matrices.     

Investigation into the surface modification of aragonite whiskers

Aragonite whiskers (AWs) were treated with several fatty acid surfactants and silane coupling agent in order to determine the optimal modifier by using contact angle measurements. The results revealed that the AWs modified by fatty acids showed more remarkable increase in the contact angle than by silane, suggesting the former were preferentially applied in modifying AWs. While the samples coated with fatty acids exhibited hydrophobicity with contact angles ranging from 104.08° to 137.87° with increasing of carbon chain length. Therefore, the highest contact angle of AWs treated by oleic acid was discussed in detail as an example, which was characterized by field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), thermo‐gravimetry analyses (TGA), X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR). FESEM and TEM results showed a thin layer coated on the modified sample surface. Both the results of TGA and XPS confirmed organic groups existed in the sample of AWs treated by oleic acid. FTIR demonstrated that calcium dioleate was formed in the modification process. Further, modification mechanism was proposed based on the obtained results. Copyright © 2016 John Wiley & Sons, Ltd.     

Calibration of thin-layer chromatography with flame ionization detection for the analysis of natural lipid samples

Thin-layer chromatography coupled with flame ionization detection has been used to develop a method to quantitate fish lipids. Quantitation of fractionated lipid classes is usually accomplished through calibration with standards. Our work shows that various standards within a class, such as triglycerides or free fatty acids give substantially different responses to the detector. A method has been developed in which a composite sample of salmon lipid is prepared with an internal standard. This technique eliminates the variable detector response observed for compounds within a class and provides more accurate quantitation of oils from which the calibration samples were prepared. The lipid classes quantitated were triglycerides, free fatty acids, phosphatidylethanolamine and phosphatidylcholine.     

Supercritical fluid chromatography of fish,shark and seal oils

Summary Various natural and treated fish, shark liver and seal oils have been analyzed by supercritical fluid chromatography (SFC) using a non-polar capillary column. The lipids are separated according to molecular mass. The lipid groups found included free fatty acids, cholesterol, squalene, vitamins, wax esters, cholesterol esters, diglycerides, triglycerides and ether lipids. Methods for the analysis of the marine oils depend on components present in the oil. When co-eluting lipid groups were present, modifications such as hydrogenation or TLC fractionation of the oils had to be made. In this paper applications of SFC on fish, seal and shark liver oils are presented.     

Synthesis and characterization of polyesters derived from sebacic acid,hexanediol, and hydroquinone

Oils and fats derived from animals and plants provide a good renewable source for polymer precursors. In this investigation, fatty acids derived from plant oils and diols were used as monomers to produce polyesters by melt polycondensation. Sebacic acid, hexanediol, and hydroquinone were used as precursors in the polymer synthesis. The polymers were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, three-bending point flexural test, X-ray diffraction, tensile testing, and contact angle. The resulting polyesters were blended with epoxies to create materials with an increased elongation at break without affecting other mechanical properties.     

Optimization of Fatty Acid Determination in Selected Fish and Microalgal Oils

The use of ten fatty acid methyl ester reference standards coupled with a detailed quantification method was shown to significantly optimize the fatty acid determination of selected fish and microalgal oils when compared to methods that use only one reference standard (C19:0 or C23:0) as a relative response factor. When using the mixture of ten reference standards after transesterifying oils with NaOH/BF₃, determination of total fatty acids, eicosapentaenoic acid and docosahexaenoic acid improved by an average of 7.3, 11.5 and 8.4%, respectively. Furthermore, improvements of 13.9, 18.9 and 6.8% of total fatty acids, EPA and DHA, respectively, were obtained when using the mixture of reference standards for fatty acid determination after directly extracting and transesterifying oil contained in microalgal cells with a mixture of methanol, HCl and chloroform. Fatty acid methyl ester standards dissolved in isooctane showed <5% variability throughout 130 days of stability testing when stored at ?20 °C. The optimized method can be used for improving the quantification of fatty acids in both oils (fish and microalgal oils) and dry microalgal cells.     

毛细管气相色谱法测定深海鱼油中的EPA和DHA含量

用氢氧化钾－甲醇酯化法将深海鱼油中的脂肪酸快速、有效地转化成脂肪酸甲酯,然后进行毛细管气相色谱法测定,以二十二碳饱和脂肪酸甲酯为内标物,建立了5,8,11,14,17－二十碳五烯酸（EPA）和4,7,10,13,16,19－二十二碳六烯酸（DHA）的定量分析方法,并用于实际样品分析。该方法对EPA和DHA定量分析的相对标准偏差分别为4．6％和5．0％,回收率分别为99．7％和99．4％。     

Analysis of Free Fatty Acids on the Fingertips by High Performance Liquid Chromatography

Abstract

This investigation studied the efficiency of high performance liquid chromatography in the determination of free fatty acids present on the fingertips, and assessed the quantitative relationship between skin fatty acids and the degree of microbial contamination. Automated surgical scrub was utilized to eliminate the microbial contamination.

The high performance liquid chromatography provided excellent separation of skin fatty acids for evaluation with the bacterial counts. The fatty acid peaks identified ranged in chain length from C12 through C32. All the fatty acids evaluated showed positive correlation with the bacterial counts with the exception of one acid which had an inverse relationship but none were statistically significant. Finally, the surgical scrub chromatograms showed that the straight chain acids C19 and C21 were lower in concentration than C23 and C25; also, C26 was lower in concentration than C28 and C30.

It was evident from the data that fatty acids which have been shown to be bacteriostatic in vitro do not demonstrate the same property on the fingertips. The finding of lower concentration of C19, C21, and C26 than longer chain acids is inconsistent with simple two carbon addition, and indicates there is possible branching at these points in metabolic pathway of fatty acid synthesis.     

Studies on SDLC (Sodium Dilauraminocystine) and SDMC (Sodium Dimyristaminocystine) Gemini Surfactants

The present work reports the synthesis and evaluation of surface active properties of amino acid-based gemini surfactants, namely, sodium dilauraminocystine (SDLC) and sodium dimyristaminocystine (SDMC) derived from L-cystine and fatty acids. The effect of reaction variables like molar ratio of raw materials and temperature has been studied for the synthesis of these gemini surfactants. In preparation of these gemini surfactants, fatty acids (lauric/myristic) were reacted with thionyl chloride to obtain respective acid chlorides (lauroyl/myristoyl). These acid chlorides were further reacted with L-cystine at different reaction conditions to get amino acid based-gemini surfactants. The study revealed that 1:2.5 molar ratio of reactants, namely, L-cystine and lauroyl/myristoyl chloride and 10–15° reaction temperature resulted in maximum yield of amino acid-based gemini surfactants (SDLC and SDMC). Surface active properties of synthesized gemini surfactants (SDLC and SDMC) were also compared with their corresponding monomeric units, namely, sodium lauroyl cysteine (SLC) and sodium myristoyl cysteine (SMC), respectively. The results demonstrated that gemini surfactants (SDLC and SDMC) had better surface active properties than their corresponding monomeric units. The structures of synthesized amino acid-based gemini surfactants were also confirmed by FTIR, ¹H NMR, ¹³C NMR, and ESI-MS spectral data.     

In Vitro and In Vivo Digestibility of Soybean,Fish, and Microalgal Oils,and Their Influences on Fatty Acid Distribution in Tissue Lipid of Mice

The digestion rates of microalgal (docosahexaenoic acid, DHA, 56.8%; palmitic acid, 22.4%), fish (DHA, 10.8%; eicosapentaenoic acid, EPA, 16.2%), and soybean oils (oleic, 21.7%; linoleic acid, 54.6%) were compared by coupling the in vitro multi-step and in vivo apparent digestion models using mice. The in vitro digestion rate estimated based on the released free fatty acids content was remarkably higher in soybean and fish oils than in microalgal oil in 30 min; however, microalgal and fish oils had similar digestion rates at longer digestion. The in vivo digestibility of microalgal oil (91.49%) was lower than those of soybean (96.50%) and fish oils (96.99%). Among the constituent fatty acids of the diet oils, docosapentaenoic acid (DPA) exhibited the highest digestibility, followed by EPA, DHA, palmitoleic, oleic, palmitic, and stearic acid, demonstrating increased digestibility with reduced chain length and increased unsaturation degree of fatty acid. The diet oils affected the deposition of fatty acids in mouse tissues, and DHA concentrations were high in epididymal fat, liver, and brain of mice fed microalgal oil. In the present study, microalgal oil showed lower in vitro and in vivo digestibility, despite adequate DHA incorporation into major mouse organs, such as the brain and liver.     

Fatty acid profile of Canadian dairy products with special attention to the trans-octadecenoic acid and conjugated linoleic acid isomers

Current scientific evidence indicates that consumption of industrial trans fatty acids (TFA) produced via partial hydrogenation of vegetable oils increases the risk of coronary heart disease. However, some studies have suggested that ruminant TFA, especially vaccenic acid (VA or 11t-18:1) and rumenic acid (RA or 9c,11t-18:2), which is a conjugated linoleic acid (CLA) isomer, may have potential beneficial health effects for humans. To date, no concerted effort has been made to provide detailed isomer composition of ruminant TFA and CLA of Canadian dairy products, information that is required to properly assess their nutritional impacts. To this end, we analyzed the fatty acid profile of popular brands of commercial cheese (n = 17), butter (n = 12), milk (n = 8), and cream (n = 4) sold in retail stores in Ottawa, Canada, in 2006-2007 by silver nitrate thin-layer chromatography and gas liquid chromatography. The average total TFA content of cheese, butter, milk, and cream samples were 5.6, 5.8, 5.8, and 5.5% of total fatty acids, respectively. VA was the major trans-octadecenoic acid (18:1) isomer in all the Canadian dairy samples with average levels of (as % total trans-18:1) 33.9% in cheese, 35.6% in butter, 31.0% milk, and 30.1% in cream. The different dairy products contained very similar levels of CLA, which ranged from 0.5 to 0.9% of total fat. RA was the major CLA isomer of all the dairy products, accounting for 82.4-83.2% of total CLA. There were no significant differences (P > 0.05) in the fatty acid profile between the 4 different dairy groups, which suggests lack of processing effects on the fatty acid profile of dairy fat.     

Liquid chromatography/electrospray ionisation mass spectrometric investigations of imidazoline corrosion inhibitors in crude oils

The so-called imidazolines (2-alkyl-1-[ethylalkylamide]-2-imidazolines and 2-alkyl-1-ethylamine-2-imidazolines) are a group of surface-active compounds, complex mixtures of which are used by various industries as surfactants and corrosion inhibitors. Although their industrial synthesis was reported over 100 years ago, few methods for the determination of individual imidazolines in mixtures, including industrial matrices such as crude oils, have been reported. Here we demonstrate that spiking of crude oils with synthetic imidazolines followed by solid-phase extraction and liquid chromatography/electrospray ionisation multistage mass spectrometry (LC/ESI - MS(n)) allows an estimation of low (<10) parts per million concentrations of individual imidazolines in crude oils. Whilst non-optimised at present, the method is a significant advance and may prove useful not only for improving an understanding of the mechanisms of industrial imidazoline synthesis and for monitoring downhole and topside oilfield operations, but also for the determination of the fate of imidazoline-based oilfield corrosion inhibitors and surfactants in the environment.     

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.     

Seed Oil Fatty Acids of Mongolian Compositae: The trans‐Fatty Acids of Heteropappus hispidus,Asterothamnus centrali‐asiaticus and Artemisia palustris

Seed oils from the Compositae plant family are known to contain a variety of unusual fatty acids. Subsequent to the recent discovery of γ‐linolenic acid in Saussurea and Youngia, further Mongolian Compositae species were investigated for their seed oil fatty acid composition. A number of δ3trans‐fatty acids (16 : 1δ3t, 18 : 1δ3t and 18 : 3δ3t, 9c, 12c) were found in the seed oils of Heteropappus hispidus and Asterothamnus centrali‐asiaticus. The latter fatty acid, but not the trans‐monoenes, was also found in one species of Artemisia. These unusual fatty acid isomers were characterized by capillary gas‐liquid chromatographic (GLC) separations in combination with other chromatographic techniques (analytical thin layer chromatography, TLC and preparative argentation TLC), and infrared spectrocsopy (IR). Their identity was further confirmed by co‐chromatography with other seed oils known to contain these trans‐fatty acids. The fact that within the Compositae plant family there are apparently two or three distinct groups of genera containing δ3trans‐fatty acids is discussed.