cis-Vaccenic acid in pulp lipids of commonly available fruits

Fatty acids of commonly available fruit pulps have been analyzed by capillary gas chromatography of their methyl esters and by gas chromatography-mass spectrometry as their dimethyl disulfide adducts. The gas chromatographic and mass spectrometric data proved that these fruits always containedcis-vaccenic (cis-11-octadecenoic) acid as a component fatty acid of their pulp lipids. The concentration ofcis-vaccenic acid in total octadecenoic acids ranged from 1.9% to 95.1% in the fruit pulps examined. The highest concentration of this acid was detected in pulp lipids of Japanese persimmon (Diospyros kaki). In fruit pulp lipids,cis-vaccenic acid was a common octadecenoic acid as well as oleic acid.     

Lipids of the pawpaw fruit: Asimina triloba

The fatty acid composition and structure of pawpaw fruit (Asimina triloba) triglycerides were examined and found to contain fatty acids ranging from C₆ to C₂₀. Octanoate represented 20% of the fatty acids while other medium-chain fatty acids were present in low amounts. Analysis of the intact triglycerides by high-temperature gas-liquid chromatography gave an unusual three-cycle carbon number distribution. Analysis of triglyceride fractions separated according to degree of unsaturation suggested that one octanoate was paired with diglyceride species containing long-chain fatty acids. Determination of the double-bond positions of monoene fatty acids revealed cis Δ9 and cis Δ11 hexadecenoate and cis Δ9, cis Δ11, and cis Δ13 octadecenoate isomers were present in significant quantities. Octanoate and positional monoene fatty acid isomers were found only in the fruit lipids and not in the seed lipids. Phenacyl esters of fatty acids were found to be useful derivatives for structure determination using multiple types of analyses.     

Occurrence of n−5 monounsaturated fatty acids in jujube pulp lipids

The pulp lipids of jujube (Zizyphus jujuba var.inermis) fruit have been shown by chromatographic, spectrometric and chemical analyses to contain a series ofcis-monoenoic fatty acids with n−5 unsaturation as major acyl moieties. The total concentration of these n−5 fatty acids, such as 14∶1n−5, 16∶1n−5 and 18∶1n−5, ranged from 22 to 54% of total fatty acids in the pulp lipids of 11 different sources. The main component of the n−5 homologues was 16∶1n−5 in all cases. Other monoenoic acids with n−7 unsaturation, namely palmitoleic (cis-9-hexadecenoic) acid andcis-vaccenic (cis-11-octadecenoic) acid, as well as with n−9 unsaturation, namely oleic acid, were also identified. In the seed lipids of jujube fruit, none of the n−5 monoenoic acids could be detected. Thus the jujube pulp lipids are characterized by the predominance of n−5 monoenoic acid isomers.     

Measurement oftrans and other isomeric unsaturated fatty acids in butterand margarine

A procedure is described for gas liquid chromatographic determination of cis andtrans isomers of unsaturated fatty acids after fractionation of the saturated, monenoic, dienoic, and polyenoic fatty acid methyl esters by argentation thin layer chromatography. To test its reliability, the procedure was used for quantitative measurement of transisomers of unsaturated fatty acids in a known mixture of simple triglycerides containing saturated fatty acids from 4:0 to 24:0 andcis andtrans isomers of 14:1. 16:1, 18:1, and 18:2. Results of the analyses of five margarine and five butter samples are presented, together with results of infrared spectrophotometric analyses fortrans fatty acid concentrations, ultraviolet spectrophotometric analyses for conjugated fatty acid concentrations, and enzymatic analyses forcis-cis-methylene interrupted fatty acid concentrations. The combined argentation thin layer and gas Chromatographic procedure is suitable for determination of the principal fatty acids in complex food lipids such as milk fat.     

Determination of fatty acids and some undesirable fatty acid isomers in selected Turkish margarines

The fatty acid composition and total trans fatty acid content in 10 margarines produced in Turkey were determined by capillary gas chromatography and Fourier transform‐infrared spectroscopy (FT‐IR) spectroscopy. The fatty acid composition ranged as follows: saturated fatty acids, C16:0 (palmitic) 11.3 to 31.8% and C18:0 (stearic) 5.7 to 8.7%, monounsaturated fatty acids, C18:1 (oleic) 21.8 to 35.7% and C18:1 trans isomers 0.4 to 27.4%, polyunsaturated fatty acid, C18:2 linoleic acid 5.2 to 40.2%. Some positional isomers of C18:1 as cis‐11‐octadecenoic acid varied from 0.7 to 4.6% and cis‐13 trace to 2.4%. The total trans fatty acid contents were between 0.9 and 32.0% when measured with capillary gas chromatography and between 0 and 30.2% with FT‐IR spectroscopy. Some of the margarines analyzed contained trace amount of trans fatty acids which could not be detected by FT‐IR spectroscopy.     

Application of a GC-MS method using deuterated fatty acids for tracingcis-vaccenic acid biosynthesis in kaki pulp

A gas chromatographic-mass spectrometric method using [2,2-²H₂]fatty acids has been developed to trace the biosynthesis ofcis-vaccenic (cis-11-octadecenoic) acid in higher plants. The deuterated fatty acids and other unlabeled fatty acids in the biosynthetic reaction mixture were converted into bis(methylthio) derivatives and analyzed by mass chromatography. The principle of this method was based on the shift of key fragment ions (containing two deuterium atoms) due to the cleavage between the methylthio-substituted carbons. The labeled compounds were detected by the m/z values which shifted 2 mass units from those of the corresponding unlabeled compounds and estimated by a calibration curve based on the peak areas of the key fragment ions. For metabolic experiments, a homogenate fraction was prepared from the pulp part of maturing kaki (Diospyros kaki) fruit and incubated with ammonium [2,2-²H₂]palmitoleate (cis-9-hexadecenoate) or [2,2-²H₂]palmitoleoyl-CoA. The incubation resulted in the formation of detectable amounts of isotopically-labeledcis-vaccenic acid containing two deuterium atoms at the carbon chain between the double bond and the carboxyl group. This experimental evidence proved thatcis-vaccenic acid was formed from palmitoleic acid by chain elongation.     

Lipids in margarines and margarine-like foods

The lipid composition of margarines from stores in selected locations in the U.S. is reported. The lipids determined include the fatty acids, tocopherols and major plant sterols. Data are included for isomeric octadecenoic fatty acids (14 isomers or groups of isomers) and four isomeric octadecadienoic fatty acids common in partially hydrogenated vegetable fats, insofar as these are separable by capillary gas chromatography. Amounts of individual lipids found in vegetable oil margarines, spreads, imitation and diet margarines were: palmitate, 8.49 to 13.17% (normalized weight percent, calculated as triglyceride); stearate, 4.78 to 9.53%; linoleate, 6.06 to 46.39%; linolenate, 0.18 to 3.57%; α-tocopherol, 0.3 to 24.3 mg/100g; γ-tocopherol, 3.0 to 55.0 mg/100g; δ-tocopherol, 0.5 to 18.9 mg/100g; campesterol, 10.6 to 106.3 mg/100g; stigmasterol, 13.1 to 60.9 mg/100g; sitosterol, 42.3 to 412.9 mg/100g. Amounts oftrans-unsaturated octadecenoic fatty acids in these margarines varied from 10.74 to 30.06%. Small amounts of thetrans,trans, trans,cis andcis,trans isomers of linoleate also are reported.     

Positional distribution of fatty acids in cardiolipin of mitochondria from 21-day-old rats

Pure cardiolipins (1,3-diphosphatidylglycerol) were prepared from mitochondria of heart, liver and kidney from 21-day-old male Wistar rats and submitted toNaja naja venom phospholipase A₂ (EC 3.1.1.4) action. Incubation conditions were controlled carefully, and a complete hydrolysis of cardiolipin to lysocardiolipin {di [1 (1″) acylsn-glycero-3-phosphoryl] 1′, 3′-sn-glycerol} and fatty acids from positions 2 (2″) was obtained in less than two hr practically without side reactions. Cardiolipins from the three organs contained low levels of saturated fatty acids; stearic acid accounted for 0.4–0.7% and palmitic acid for 1.4–3.5% of total fatty acids. These percentages apparently depended on the organ. In all three cases, linoleic acid was the major component, but its percentage varied from 62–78% of total fatty acids. Acyl chains linked to positions 1 (1″) of all three cardiolipin preparations exhibited a similar pattern; they were composed of linoleic acid for 85–89%. This fatty acid also was the main component esterified at position 2 (2″), but its percentage was much more variable: from 39.8% in heart to 51.2% in kidney and 67.8% in liver mitochondria. The remaining acids comprised octadecenoic and polyunsaturated fatty acids with more than 18 carbon atoms in different proportions. As opposed to other phospholipids,cis-vaccenic acid, and not oleic acid, was the main octadecenoic acid present in cardiolipins. Octadecenoic acids were nine- to 10-fold more concentrated at positions 2 (2″) than at positions 1 (1″). The percentage ofcis-vaccenic acid was four- to five-fold higher than that of oleic acid at positions 2 (2″), whereas oleic acid dominated at positions 1 (1″). From results presented in this study and selected literature data, it may be concluded that fatty acids are asymmetrically distributed in cardiolipins of different origins, with linoleic acid showing a definite preference for position 1 (1″).     

Distribution of dietary octadecenoate isomers at the 1- and 2-positions of hepatoma and liver phospholipids

Phosphatidylcholines and phosphatidylethanolamines were isolated from hepatoma 7288CTC, normal liver, and host liver of rats fed one of the following diets: fat-free diet; fat-free diet supplemented with safflower oil, safflower oil fatty acids, or partially hydrogenated safflower oil fatty acids; and commercial chow. Thecis andtrans octadecenoate fatty acids were isolated from the 1- and 2-positions of both phosphoglycerides and analyzed quantitatively for chain positional isomers. Octadecenoates from hepatoma and liver phosphoglycerides of animals fed fat-free or natural fatsupplemented diets contained almost exclusively twocis isomers: oleic and vaccenic acids. Oleic acid predominated in the 2-position octadecenoates of both phosphoglycerides from hepatoma and liver. In contrast, vaccenic acid predominated in the 1-position of normal liver phosphatidylcholine and, to a lesser extent, phosphatidylethanolamine. Host liver and hepatoma exhibited a shift to a higher percentage of oleic acid at the 1-position. Dietarytrans fatty acids were incorporated predominately in the 1-position of both phosphoglycerides of hepatoma and liver. Except for thecis Δ10 octadecenoate isomer, all of the unnatural dietarycis isomers between Δ8 and Δ14 were incorporated into the 1-position of the phospholipids, while the unnaturalcis octadecenoates at the 2-position consisted primarily of the Δ12 isomer. Hepatoma phosphoglycerides contained higher percentages of thetrans Δ10 isomer that was nearly excluded from the 1-position of the two liver phosphoglycerides. All the othertrans octadecenoate isomers were incorporated into the 1-position of both phosphoglycerides, but the small amount oftrans fatty acids incorporated into the 2-position of liver and hepatoma phosphatidylcholine consisted of four isomers, Δ9 to Δ12, including the Δ10 isomer. Phosphatidylethanolamine exhibited a similar distribution, except for the presence of the Δ13 and Δ14 isomers at the 2-position. A combination of evidence suggests that the 1-position fatty acids in phosphatidylcholine and phosphatidylethanolamine are of similar origin. The octadecenoates at the 2-position of these two phosphoglycerides appear to be of the same origin in hepatoma but not in liver. It was also revealed that the 2-position of hepatoma phosphatidylcholine contained much higher percentages of palmitate than liver.     

Trans- and cis-octadecenoic acid isomers in the hump and milk lipids from Camelus dromedarius

The distribution profiles of individual trans- as well as cis-18∶1 isomers from the fat prepared from the hump adipose tissue and the milk from Camelus dromedarius (the single-humped Arabian species) are described. Gas-liquid chromatography on two capillary columns with different polarities and lengths were used for this purpose in combination with argentation thin-layer chromatography. A comparison of the profiles established is made with that of true ruminant fats. In the fats from the dromedarius as well as from true ruminants, the trans-18∶1 isomers have their ethylenic bonds in all positions between Δ4 and Δ16. The prominent trans isomer is the 11–18∶1 (vaccenic) acid in all species, and the complete distribution profiles are quite similar. Concerning the cis isomers, the prominent isomer is oleic acid, followed by cis-vaccenic acid, as in true ruminant fats. Other cis isomers encompass the Δ6–8 and the Δ12 to Δ15 isomers. Camelidae (suborder Tylopoda) and Bovidae (suborder Ruminantia) have evolved independently since the Eocene, that is for approximately 50 million years. Despite this considerable period, and the profound differences in anatomy, morphology, physiology, ecological and dietary habits between the extant species of these suborders, the rumen microflora has continued to synthesize the same trans- and cis-octadecenoic acid isomers, in comparable proportions, at least as deduced from their composition profiles. We conclude that the trans-18∶1 acid profile is not intrinsically species-dependent, but it can be affected by the nature and the proportions of dietary unsaturated fatty acids that themselves depend on the feed, and that may be species-specific.     

Fatty acid and conjugated linoleic acid isomer profiles in human milk fat

The fatty acid composition of 39 mature human milk samples from four Spanish women collected between 2 and 18 weeks during lactation was studied by gas chromatography. The conjugated linoleic acid (CLA) isomer profile was also determined by silver‐ion HPLC (Ag⁺‐HPLC) with three columns in series. The major fatty acid fraction in milk lipids throughout lactation was represented by the monounsaturated fatty acids, with oleic acid being the predominant compound (36–49% of total fatty acids). The saturated fatty acid fraction represented more than 35% of the total fatty acids, and polyunsaturated fatty acids ranged on average between 10 and 13%. Mean values of total CLA varied from 0.12 to 0.15% of total fatty acids. The complex mixture of CLA isomers was separated by Ag⁺‐HPLC. Rumenic acid (RA, cis‐9 trans‐11 C18:2) was the major isomer, representing more than 60% of total CLA. Trans‐9 trans‐11 and 7‐9 (cis‐trans + trans‐cis) C18:2 were the main CLA isomers after RA. Very small amounts of 8‐10 and 10‐12 C18:2 (cis‐trans + trans‐cis) isomers were detected, as were different proportions of cis‐11 trans‐13 and trans‐11 cis‐13 C18:2. Although most of the isomers were present in all samples, their concentrations varied considerably.     

Metabolic aspects of positional monounsaturated fatty acids isomers

Absorption and distribution of positionalcis andtrans octadecenoic acid isomers in lipids from rat, egg and human tissues are reviewed. Selected data on enzyme, single-cell, and whole-animal studies with positional octadecenoic acid isomers are summarized and compared.     

Placental transport oftrans fatty acids in the rat

Placental transport of 9-trans [1-¹⁴C] octadecenoic (elaidic) and 9-trans,12-trans [1-¹⁴C] octadecadienoic (linoelaidic) acids was demonstrated in rats. On the 18th day of gestation, a¹⁴C-labeled albumin complex of elaidic or linoelaidic acid was injected into the jugular vein of pregnant rats. For comparison, 9-cis [1-¹⁴C] octadecenoic (oleic) or 9-cis,12-cis [1-¹⁴C] octadecadienoic (linoleic) acid also was injected into the maternal circulation of rats. All animals were sacrificed 1 hr following injection. Lipid composition and distribution of label were determined in maternal plasma, placental and fetal tissues. Differences in specific activities of plasma, placental and fetal total lipids indicated a decreasing concentration gradient for bothcis andtrans isomers of octadecenoic and octadecadienoic acids. Distribution of radioactivity in various lipid components was determined by thin layer chromatography. Irrespective of the label, the highest percentage of total radioactivity was carried by triglycerides (TG) in maternal plasma (∼60–80%), and was incorporated mainly in phospholipids (PL) of fetal tissues (∼50–60%). A nearly equal distribution of the label was found between PL and TG of placental lipids (∼40%). Radioactivity of fatty acid methyl esters (FAME) determined by radiogas liquid chromatography indicated that after injection of linoelaidate, radioactivity of maternal plasma, placental and fetal tissue FAME was associated only witht,t-18∶2. Following injection of elaidate, all the radioactivity in placental FAME was associated witht-18∶1; however, in fetal tissues, the label was distributed between 16∶0 andt-18∶1. These findings suggest that, in contrast to linoelaidic acid, rat fetal tissues can metabolize elaidic acid via β oxidation to form acetyl CoA and palmitic acid.     

Synthesis of octadecynoic acids and [1-14C] labeled isomers of octadecenoic acids

Geometric and positional isomers of [1-¹⁴C] octadecenoic acids have been synthesized by modifications of published procedures. Positional isomers of octadecynoic acids also have been synthesized to obtain the geometric and positional isomers of the unlabeled octadecenoic acid analogs. The syntheses were accomplished by coupling a haloalkyl compound with a substituted acetylene using n-butyl lithium in hexamethylphosphoramide. The coupled product, either a 17-or 18-carbon acetylenic alcohol, could be semihydrogenated and chain extended to afford a carboxy labeled derivative, could be partially hydrogenated and chain extended to afford a carboxyl labeledcis-ortrans-octadecenoic acid in the former case. In the latter case, octadecynoic,cis-octadecenoic ortrans-octadecenoic acids could be obtained by the appropriate reactions. The methods used in this study enabled the synthesis of¹⁴C-labeled fatty acids in generally higher yields and by simpler reactions than were previously possible.     

Dibutyrate derivatization of monoacylglycerols for the resolution of regioisomers of oleic, petroselinic, and cis-vaccenic acids

Dibutyrate derivatives of monoacylglycerols of oleic, petroselinic, and cis-vaccenic acids were prepared by diesterification of monoacylglycerols with n-butyryl chloride. The resulting triacylglycerols were analyzed by gas chromatography (GC) with a 65% phenyl methyl silicone capillary column and separated on the basis of both fatty acid composition and regiospecific position. The petroselinic acid derivatives eluted first, followed sequentially by the oleic and cis-vaccenic acid derivatives, with the sn−2 positional isomer eluting before the sn−1(3) isomer in each case. Separation of the peaks was almost baseline between petroselinic and oleic acids as well as between oleic and cis-vaccenic acids. To assess the accuracy of the method, mixtures of triolein, tripetroselinin, and tri-cis-vaccenin in various known proportions were partially deacylated with the use of ethyl magnesium bromide and derivatized and analyzed as above. The results showed that this method compares favorably to the existing methods for analysis of oleic, petroselinic, and cis-vaccenic fatty acids by GC with respect to peak separation and accuracy, and it also provides information on the regiospecific distribution of the fatty acids. The method was applied to basil (Ocimum basilicum) and coriander (Coriandrum sativum) seed oils. cis-Vaccenic, oleic, and linoleic acids were mainly distributed at the sn−2 position in basil seed oil, and higher proportions of linolenic, palmitic, and stearic acids were distributed at the sn−1(3) position than at the sn−2 position. In coriander seed oil, petroselinic acid was mainly distributed at the sn−1(3) position, and both oleic and linoleic acids were mostly located at the sn−2 position, whereas palmitic, stearic, and cis-vaccenic acids were located only at the sn−1(3) position.     

Sequential gas chromatographic procedure for microanalysis of monoenoic double bond position in hydrogenated oils

Quantitative cleavage of epoxyoctadecanoates with periodic acid (HIO₄) has been demonstrated and the technique incorporated into an all gas chromatographic system for detailed lipid analysis. The overall procedure involves three sequential gas chromatographic separations interspersed by two microreactions. By this procedure, a complete analysis forcis- andtrans-geometric isomers corresponding to each positional octadecenoate isomer is obtained. Total sample requirements are less than 10 mg, and the elapsed analysis time/sample is less than 10 hr. In this all gas chromatographic procedure, a lipid methyl ester sample is first separated by preparative gas chromatography, and the monoene fraction is collected and epoxidized. Next, the epoxidized sample is separated by gas chromatography intocis- andtrans-epoxyoctadecanoate fractions. These epoxyoctadecanoate fractions are collected and cleaved with HIO₄ into aldehyde and aldehyde-ester fragments, which are quantitatively analyzed by gas chromatography. The double bond positions are determined from the aldehyde and aldehyde-ester cleavage data, which are stored and processed by a computerized on-line gas chromatographic data acquisition system. The procedure was tested on pure octadecenoate isomers, standard mixtures, and commercially hydrogenated vegetable oils. Analyses of hydrogenated vegetable oils are compared with data acquired by reverse-phase and argentation chromatography followed by reductive ozonolysis. Presented at the AOCS Meeting, April 1973, New Orleans. ARS, USDA.     

Lactobacillic and methyl-branched olefinic acids inByrsocarpus coccineus seed oil

A detailed investigation of the seed oil ofByrsocarpus coccineus Schum. and Thonn. has disclosedcis-11,12-methyleneoctadecanoic (lactobacillic) (13%) and two branched octadecenoic acids (0.1%). Other fatty acids in the oil are those normally associated with seed lipids except for an unusually high proportion (12%) ofcis-11-octadecenoic acid. Lactobacillic acid has long been known as a constituent of certain bacterial lipids, but this is the first report of its presence in a seed oil. The branched olefinic acids have not heretofore been found to occur in plants. Mention of firm names or trade products does not imply endorsement or recommendation by the Department of Agriculture over other firms or similar products not mentioned.     

Effect of methyl 2-hexadecynoate on hepatic fatty acid metabolism

Normal and hepatoma bearing rats were fed a low level of methyl 2-hexadecynoate in a low fat diet for one month. The effect of the acetylenic acid on lipid metabolism as derived from mass analysis of lipid classes, fatty acids and positional monoene isomers isolated from the major lipid classes of liver and hepatoma has been assessed. Methyl 2-hexadecynoate caused a 25% decrease in body weight and the appearance of essential fatty acid deficiency symptoms within one week. Non-tumor-bearing animals contained a seven-fold increase in all neutral lipid classes, except cholesterol, while host animals did not contain fatty livers. The apparent protective effect of the host animal by the hepatoma also resulted in only marginal changes in the fatty acid and positional monoene isomers from host liver and hepatoma lipids. In contrast to host liver and hepatoma, methyl 2-hexadecynoate caused a massive accumulation of palmitate and hexadecenoates with a concomitant decrease in stearate and octadecenoates in most of the lipid classes from non-tumor-bearing animals. These changes were accompanied by a shift from the higher molecular weight triglycerides to lower molecular weights corresponding to carbon number 48. The high concentrations of hexadecenoates consisted predominantly of the Δ9 isomer. Despite the high concentrations ofcis Δ9 hexadecenoate, precursor ofcis Δ11 octadecenoate (vaccenate), total vaccenate levels of the five major lipid classes were lower than control values. All of these data strongly suggest that long-chain 2-ynoic acids inhibit elongation of saturated and monoene fatty acids.     

Study of individual trans- and cis-16∶1 isomers in cow, goat, and ewe cheese fats by gas-liquid chromatography with emphasis on the trans-Δ3 isomer

Low-temperature gas-liquid chromatography (GLC) was applied to study the distribution profiles of isomeric trans-and cis-hexadecenoic acids in ruminant (cow, goat, and ewe) milk fat after their fractionation by argentation thin-layer chromatography (Ag-TLC). The fat was extracted from cheeses (12 samples of each species), the most common foods made with goat and ewe milks. The predominant trans-16∶1 isomer is palmitelaidic acid (the Δ9 isomer), but it does not exceed one-third of the total group, which itself represents 0.17% (cow), 0.16% (goat), and 0.26% (ewe) of the total fatty acids. The trans-Δ3 16∶1 isomer, which is reported for the first time in ruminant lipids and which likely comes from the animals' feed, is present at a level of ca. 10% of the trans-16∶1 acid group. Otherwise, all isomers with their ethylenic bond between positions Δ4 and Δ14 are observed in the three species studied, roughly showing the same relative distribution pattern. Quantitatively, the trans-16∶1 isomers only represent ca. 5% of the sum of the trans-16∶1 plus trans-18∶1 isomers, and they appear of little importance in comparison. It is inferred from this and recent studies that some previously reported data that were established for consumption assessments dealt in fact mainly with iso-17∶0 acid, which was confused with (and added to) trans-Δ9 (palmitelaidic) acid; consequently, these results were large overestimates. Regarding the cis-16∶1 acids, the Δ9 isomer is the prominent constituent as expected, but the second-most important isomer is the Δ13 isomer. It does not appear that trans-16∶1 isomers are from ruminant milk fats of great nutritional importance as compared with trans-18∶1 isomeric acids. As for trans-18∶1 isomers, the combination Ag-TLC/GLC is a necessary procedure to quantitate trans-16∶1 acids accurately and reliably. Ag-TLC allows removal of interfering branched 17∶0 acids and cis-16∶1 acids, and low-temperature GLC permits an accurate measurement of all individual isomers most of which with baseline resolution.     

Monoenoic fatty acids in human brain lipids: Isomer identification and distribution

The carbon chain length distribution and the double bond positional isomer composition of the monoenoic fatty acids of the lipids of total human brain tissue have been determined using gas chromatography and gas chromatography/mass spectrometry of the fatty acid methyl and picolinyl esters. The even chain length monoenoic C₁₆ to C₂₈ fatty acids contain predominantly two positional isomer series, the n−7 and n−9cis homologues, whose relative proportion varies significantly with chain length. The odd chain length long-chain fatty acids consist of n−8 and n−10 isomers, whereas the odd chain length very long-chain (more than 22 carbon) fatty acids are n−7 and n−9 isomers.