Hydrogenation of a menhaden oil: II. Formation and evolution of the C20 dienoic and trienoic fatty acids as a function of the degree of hydrogenation

To complement studies on monoethylenic fatty acids produced from the major polyunsaturated fatty acid (20:5A5,8,11,14,17) during hydrogenation of a menhaden oil of iodine value (IV) 159, the C₁₀ dienoic and trienoic fatty acid isomers of partially hydro-genated menhaden oils (PHMO) of IV 131.5, 96.5 and 85.5 were isolated by a combination of preparative gas liquid chromatography (GLC), mercuric adduct fractionation, and silver nitrate thin layer chromatography (AgNO₃-TLC). The 20:2 fatty acid methyl esters of the three PHMO samples were transformed to the corresponding alcohols and ozonized in BF₃-MeOH, followed by GLC analysis of the ozonolysis fragments. During the hydrogenation process, re-sidual ethylenic bonds in the 20:2 isomers tend to migrate both towards the carboxyl group and towards the methyl end of the molecule. The hydrazine reaction results revealed that thetrans ethylenic bonds in the 20:2 and 20:3 isomers were distributed all along the the carbon chain, but thecis ethylenic bonds were more localized in the Δ11,Δ14 and Δ17 positions of the preexisting major menhaden oil component 20:5Δ5,8,11,14,17. Iatroscan analyses on AgNO₃-chromarods revealed that, as a result of the hydrogenation process, almost half of the 20:2 isomers were non-methylene-interruptedcis, trans/trans, cis structures. Presented in part at the 73rd annual AOCS meeting, Toronto, 1982.     

Monoethylenic fatty acids of a partially hydrogenated herring oil

A Canadian Atlantic herring oil hydrogenated for margarine use to an iodine value of 76 and melting point of 32.5 C was found to have 30% saturated acids and 66% monounsaturated fatty acids. The monounsaturated fatty acids could be analytically determined ascis andtrans isomers by open tubular gas liquid chromatography.Trans acids were 33% of the C₁₆ and C₁₈ monounsaturated acids, and 32 and 28%, respectively, of the C₂₀ and C₂₂ monounsaturated acids. After separation of geometric isomers by Florisil-silver nitrate chromatography the positional isomers in each class were determined by oxidative fission. The double bond positions of the originalcis fatty acids were largely retained in bothcis andtrans isomers, but additional isomers were observed, especially in thetrans fatty acids.     

Monoethylenic isomers in cardiac lipids of rats fed partially hydrogenated herring oil

Compositional studies have been carried out to compare the monoethylenic fatty acid isomers of a partially hydrogenated herring oil with those found in the cardiac lipid of young rats fed this oil for 1 or 16 weeks. In general, all geometrical and positional isomers with chain lengths C₁₆, C₁₈, C₂₀ and C₂₂ found in the hydrogenated oil were also observed in cardiac lipid. Evidence was also obtained for the occurrence of β-oxidation in the catabolism of thecis andtrans isomers of these long chain acids. Presented at the AOCS Meeting, Ottawa, September 1972.     

Isomers of monoethylenic fatty acids in some partially hydrogenated marine oils

An analytical study of the monoethylenic isomers in commercial samples of partially hydrogenated herring, whale and seal oils is presented. The results show that with hydrogenated herring oil there is a slight decline in monoenetrans content from 37% in C₁₆ through to 32% in C₂₂. With both whale and seal oils, monoenetrans contents were constant at 54% and 59%, respectively, throughout all chain lengths. In general thecis andtrans positional isomers from hydrogenated whale and seal oils were more scattered than those from hydrogenated herring oil; however in each oil the majorcis isomers of each chainlength were indicative of originalcis fatty acid isomers in the raw oils.     

Essential fatty acid-deficient rats: II. On the fatty acid composition of partially hydrogenated arachis,soybean and herring oils and of normal,refined arachis oil

The fatty acid composition of partially hydrogenated arachis (HAO), partially hydrogenated soybean (HSO) and partially hydrogenated herring (HHO) oils and of a normal, refined arachis oil (AO) was studied in detail by means of direct gas liquid chromatography, ultraviolet and infrared spectrophotometry and by thin layer chromatography fractionation on silver nitrate-silica gel plates followed by gas liquid chromatography. It was shown that the partially hydrogenated oils all contained fatty acids withtrans double bonds. In the plant oils, thetrans acids were present mainly as elaidic acid. The HHO showed an almost equal distribution betweentrans 18∶1 ω9,trans 20∶1 ω>9 andtrans 22∶1 ω>9. Sometrans configuration was also found in the C₂₀-and C₂₂-dienes and trienes of the HHO. In all the oils, conjugated fatty acids were present in minor amounts only (<0.5%). Special attention was given to the ω-acids known to be of specific nutritional value. The HSO contained about 32% linoleic acid, whereas the content ofcis, trans+trans, cis andtrans, trans octadecadienoic isomers was 1.7% and 0.5%, respectively. The amount of linoleic acid in the HSO was even higher than that of AO (29%). The HAO contained only 0.8% 18∶2 ω6 (linoleic acid). Further, two 18∶2 fatty acids with ω>6, acis, cis and atrans, trans isomer, were present in small amounts. The HHO contained 0.5% 18∶2 ω6 (linoleic acid). Isomers of 18∶2 ω>6 were also found in the HHO. They may be hydrogenation products of higher unsaturated C₁₈-acids orginally present. All the C₂₀- and C₂₂-dienes and trienes were shown to have an ω-chain greater than 6. Fatty acids with ω6-structure were not formed during partial hydrogenation of the oils studied.     

Some minor fatty acids of rapeseed oils

A number of minor unsaturated fatty acids of rapeseed oil (fromBrassica napus orcampestris) have been isolated by combinations of distillation preparatve gas liquid chromatography and silver nitrate thin layer chromatography, and were further identified by oxidative fission in BF₃-MeOH. Among the shorter chain, all-cis polyunsaturated fatty acids described are 16:3ω3, 16:2ω6 and 14:2ω6. A ubiquitous minor component inunproceessed oils was found to becis-9, cis-12, trans-15-octadecatrienoic acid, with lesser proportions of thetrans-9, cis-12, cis-15 isomer. Among others identified werecis-14:1ω9 and 15:1ω10, the latter accompanied by half as muchtrans-15:1ω10. Particular attention was paid to the proportions of the minor monoethylenic fatty acids of the ω7 series relative to the longer chain major ω9 monoethylenic fatty acids which have been reduced by plant breeding.     

Alteration of long chain fatty acids of herring oil during hydrogenation on nickel catalyst

During hydrogenation of a refined herring(Clupea harengus) oil iodine value (IV) 119, on a commercial nickel catalyst, samples were collected at IV 108, 101, 88 and 79. In the early stages of the process, IV 119 to IV 101, the positional and geometrical isomerization of the long chain monoenoic fatty acids (20:1 and 22:1) was hindered by the stronger absorption on the catalyst surface of the polyenes with 4, 5 and 6 double bonds. Consequently at IV 101, 70% of these polyenes had been converted to dienoic and trienoic fatty acids, but only 3-4%trans 20:1 and 22:1 accumulated. As the hydrogenation proceeded, IV 101 to IV 79, the originaleis 20:1 and 22:1 isomers (mainly Δ11 with some ΔA9 and Δ13) decreased and new positional and geometrical isomers (both cis andtrans in positions Δ6 to Δ15) were formed. The majortrans isomers were Δ11 accompanied by important proportions of Δ10 and Δ12. At IV 79, moretrans 20:1 (ca. 36%) thantrans 22:1 (ca. 29%) was detected. Monoethylenic fatty acids newly formed from polyethylenic fatty acids made only minor contributions to the total 20:1 and 22:1 at these levels of hydrogenation, but a “memory effect” which skews the proportions of minorcis andtrans isomers can be attributed to the proportions of minorcis 22:1 isomers (Δ9, Δ13 and Δ15) orginally present. Presented in part at AOCS Annual Conference, San Francisco, May 1979.     

Trans-6-hexadecenoic acid and the corresponding alcohol in lipids in the sea anemoneMetridium dianthus

Trans-6-hexadecenoic acid was found in polar lipids, triglycerides, was esters and diacylglyceryl ethers of the sea anemoneMetridium dianthus from Passamaquoddy Bay. The corresponding alcomaquoddy Bay. The corresponding alcohol also apparently occurs in the wax esters of this species. The long-chain (C₂₀, C₂₂) monoethylenic alcohols reported for other species of sea anemones from neighboring waters were absent and the major alcohol and glyceryl ether chain both had 16∶0 structures. The isomers of C₁₈ and C₂₀ monoethylenic fatty acids in polar lipids and triglycerides were unusual in their high proportion of theω ₇ isomer. These two lipids also contained higher proportion of the polyunsaturated fatty acids than the others.     

Influence of Various Reaction Parameters on the Reactivities of Highly Unsaturated Fatty Acids During a Partial Hydrogenation on Nickel Catalyst and on the Formation of Isomeric Mono- and Di-Ethylenic Acids

A refined menhaden oil of iodine value (IV) of 189 was hydrogenated on nickel catalyst under different temperatures, rates of agitation, hydrogen pressures and nickel content. Samples were collected during each hydrogenation in order to calculate the selectivities of the different C₂₀ fatty acid classes (dienes, pentaenes). In each case, a large difference in reactivities was observed between the 20:1 and 20:2 acids, but the 20:3, 20:4 and 20:5 acids had similar behaviours toward the nickel catalyst. The reaction parameters had a great influence on the 20:2 selectivity. However they did not apparently affect the 20:3, 20:4 or 20:5 selectivity values. The 20:1 and 20:2 isomer distributions also depended on the reaction parameters. For the 20:1 acids, an accumulation of isomers with the ethylenic bonds close to the carboxyl group, especially cis Δ 5, trans Δ 5 and trans Δ 6, was observed at high temperatures. The results can be interpreted as the combination of a substantial migration of ethylenic bonds and simultaneously a preferential hydrogenation of those ethylenic bonds farthest removed from the carboxyl group.     

Application of methoxy-bromomercuri-adduct fractionation to the analysis of fatty acids of partially hydrogenated marine oils

The fatty acids of a refined and of a partially hydrogenated menhaden oil, iodine value (IV) 84.5, were separated into different classes (e.g., monoene, diene, including pentaene and hexaene) by thin layer chromatography (TLC) of their methoxy-bromomercuri-adducts (MBM). In the solvent system hexane: dioxane, the separation of fatty acids occurred according to the degree of unsaturation. No influence was exerted by either the geometry or the position of the ethylenic bonds. The effect of the various chain lengths (C₁₄−C₂₂) was to broaden the bands, but no overlap occurred among the chain lengths. A wide range of C₂₀ unsaturated fatty acids were prepared by the hydrazine reduction of 20∶5-Δ5,8,11,14,17. These were separated into groups as MBM adducts and identified by comparison of their experimental and calculated equivalent chain lengths (ECL) in gas liquid chromatography (GLC) on SILAR-5CP and SILAR-7CP columns. This confirmed that GLC did not totally separate all groups of isomers of different degrees of unsaturation. The quantitative analysis of both refined and partially hydrogenated (IV-84.5) menhaden oils by GLC was effected by the recovery of the fatty acid methyl esters from the MBM adduct TLC bands with the addition of methyl heptadecanoate (17∶0) as an internal standard, followed by analysis of the different fractions on open-tubular columns coated with SILAR-5CP. For methylene- and nonmethylene-interrupted unsaturated acids, 100% recovery from the MBM adducts was achieved, but in the case of the conjugated dienes the maximal recovery was 70%.     

Heat treatment of vegetable oils. II. GC-MS and GC-FTIR spectra of some isolated cyclic fatty acid monomers

Gas liquid chromatography coupled with mass spectrometry (GC-MS) showed that the cyclic fatty acid monomers (CFAM) isolated from a heated linseed oil have two ethylenic bonds, while the CFAM isolated from heated sunflower oils were saturated and monoethylenic isomers. GC-MS studies also showed the presence of cyclohexenic derivatives in the case of linseed oil. GLC coupled with Fourier transform infrared spectrometry (GC-FTIR) studies indicated that the CFAM isolated from linseed oil were ofcis (Z),trans (E) structures except two components which werecis,cis (Z,Z) dienoic acids. The unsaturated CFAM isolated from sunflower oils werecis (Z) andtrans (E) monoethylenic isomers. For sunflower oils, the major CFAM were isomers having acis (Z) ethylenic bond. The saturated CFAM isolated from a heated sunflower oil had molecular weights of 296 and 294. The latter could correspond to some bicyclic isomers.     

The electrochemical hydrogenation of edible oils in a solid polymer electrolyte reactor. II. Hydrogenation selectivity studies

Soybean oil has been hydrogenated electrochemically in a solid polymer electrolyte (SPE) reactor at 60°C and 1 atm pressure. These experiments focused on identifying cathode designs and reactor operation conditions that improved fatty acid hydrogenation selectivities. Increasing oil mass transfer into and out of the Pd-black cathode catalyst layer (by increasing the porosity of the cathode carbon paper/cloth backing material, increasing the oil feed flow rate, and inserting a turbulence promoter into the oil feed flow channel) decreased the concentrations of stearic acid and linolenic acid in oil products [for example, an iodine value (IV) 98 oil contained 12.2% C_18:0 and 2.3% C_18:3]. When a second metal (Ni, Cd, Zn, Pb, Cr, Fe, Ag, Cu, or Co) was electrodeposited on a Pd-black powder cathode, substantial increases in the linolenate, linoleate, and oleate selectivities were observed. For example, a Pd/Co cathode was used to synthesize an IV 113 soybean oil with 5.3% stearic acid and 2.3% linolenic acid. The trans isomer content of soybean oil products was in the range of 6–9.5% (corresponding to specific isomerization indices of 0.15–0.40, depending on the product IV) and did not increase significantly for high fatty acid hydrogenation selectivity conditions.     

Improved methods for the isolation and study of the C18, C20 and C22 monoethylenic fatty acid isomers of biological samples: Hg adducts,HPLC, AgNO3-TLC/FID,and ozonolysis

The monoethylenic isomers of C₁₈, C₂₀ and C₂₂ chain lengths of the depot fat of a nonhominid primate (cynomolgus monkeys,Macaca fascicularis), fed a partially hydrogenated herring oil (IV=76.0) for 30 months, were examined by 2 different approaches. The first isolation method involved preparative gas liquid chromatography and argentation thin layer chromatography (TLC). The second sequence involved a chain-length fractionation system based on the TLC of the methoxy-bromomercuri quence involved a chain-length fractionation system based on the TLC of the methoxy-bromomercuri adducts of the total methyl esters to isolate groups of acids of common degrees of unsaturation, and then high performance liquid chromatography on a reverse-phase column. In both cases, the monoethylenic isomer distribution was determined by ozonolysis in BF₃/MeOH. Comparable results were obtained with the 2 methods. The second approach is recommended for small biological samples, especially for those containing a relatively high proportion of di- and other polyethylenic isomers which might interfere. Presented in part at the AOCS annual meeting, New Orleans, May 1981.     

Effects of hydrogenation parameters on trans isomer formation,selectivity and melting properties of fat

Effects of hydrogenation conditions (temperature, hydrogen pressure, stirring rate) on trans fatty acid formation, selectivity and melting behavior of fat were investigated. To this aim, soybean oil was hydrogenated under various conditions and fatty acid composition, trans isomer formation, slip melting point (SMP), solid fat content (SFC) and iodine number (IV) of the samples withdrawn at certain intervals of the reactions were monitored. A constant ratio (0.03%) of Nysosel 222 was used in the various combinations of temperature (150, 165 and 180 °C), stirring speed (500, 750 and 1000 rpm) and hydrogen pressure (1, 2 and 3 bar). Raising the temperature increased the formation of fatty acid isomers, whereas higher stirring rates decreased this formation, while changes in hydrogen pressure had no effect or slightly reduced it, depending on other parameters. Results also indicated that the trans fatty acid ratio increased with IV reduction, reached the highest value when the IV was about 70 and decreased at IV < 70 due to saturation. Selectivity values (S₂₁) at that point ranged between 5.78 and 11.59. Lower temperatures and higher stirring rates decreased not only the trans isomer content but also the S₂₁ values at significant levels. However, same effects were not observed with the changes in hydrogen pressure. It was determined that a high SMP does not necessarily mean a high SFC. Selective conditions produced samples with higher SFC but lower SMP, which is possibly because of higher trans isomer formation as well as lower saturation.     

Quantitative analysis of long-chain trans-monoenes originating from hydrogenated marine oil

Gas chromatography (GC) is used for the analysis of trans-fatty acids in partially hydrogenated vegetable oils. Although trans-isomers of C₁₈ carbon length predominate in partially hydrogenated vegetable oils, trans-isomers of C₂₀ and C₂₂ carbon length occur in partially hydrogenated fish oil. We report a simple silver ion chromatographic combined with capillary GC technique for quantitative analysis of trans-monoenes derived from partially hydrogenated fish oil. Silver nitrate thinlayer chromatographic (TLC) plates are developed in toluene/hexane (50∶50, vol/vol). Fatty acid methyl esters are separated into saturates (R _f 0.79), trans-monoenes (R _f 0.49), cis-monoenes (R _f, 0.27), dienes (R _f, 0.10), and polyunsaturated fatty acids with three or more double bonds remaining at the origin. The isolated trans-monoenes are quantitatively analyzed by capillary GC. The technique of argentation TLC with GC analysis of isolated methyl esters is highly reproducible with 4.8% variation (i.e., coefficient of variation, CV%) in R _f values and 4.3 and 6.9% CV% in quantification within batch and between batch, respectively. Furthermore, the combined technique revealed that direct GC analysis underestimated the trans-content of margarines by at least 30%. In this study, C₂₀ and C₂₂ trans-monoenes were found in relatively large quantities; 13.9% (range 10.3–19.6%) and 7.5% (range 5.3–11.5%), respectively, in margarine purchased in 1995, but these C₂₀ and C₂₂ trans-monoenes were much reduced (0.1%) in a fresh selection of margarine purchased in 1998. Compositional data from labels underestimated the trans-content of margarines, especially those dervied from hydrogenated marine oil. Low levels of C₂₀ trans-monoenes (range 0.1–0.3%) and C₂₂ trans-monoenes (range 0.0–0.1%) were identified in adipose tissue obtained from healthy volunteers in 1995, presumably indicating consumption of partially hydrogenated fish oil.     

Continuous hydrogenation of fats and fatty acids at short contact times1

Continuous hydrogenation of fats and fatty acids using suspended catalysts was studied in a vertical flow reactor packed with Raschig rings. A short time of reactive contact of the fat or the fatty acid with the catalyst and hydrogen is the unique feature of this system. A nickel catalyst used in the hydrogenation of soybean oil gave a reduction of 40-50 iodine value units per min, small amounts oftrans-isorners (10-20%), large proportions of linoleate in unreduced octadecadienoyl moieties (70-80%), and nonselective reduction of polyunsaturated acyl moieties (linoleate selectivity ratio 1-3). Another nickel catalyst, used in the hydrogenation of tallow fatty acids, also gave a reduction of 40-50 iodine value units per min and nonselective reduction of polyunsaturated fatty acids. A copper chromite catalyst used in the hydrogenation of soybean oil gave a reduction of 10-15 iodine value units per min, low levels oftrans- isomers (10-15%), and selective reduction of linolenoyl moieties (linolenate selectivity ratio 4-6). Composition of positional isomers of cis- andtrans-octadecenoyl moieties in partially hydrogenated products obtained both with nickel and copper chromite catalysts reveals that essentially the same mechanisms of isomerization are involved in continuous hydrogenation at short time of reactive contact as in batch hydrogenation. 1The terms “linoloyl” and “linolenoyl” are used throughout to designate9-cis, 12-cis-octadecadienoyl and 9-cis, 12-cis, 15-cis- octadecatrienoyl groups, respectively.     

Identification and quantitation of cis/trans C16:1 and C17:1 fatty acid positional isomers in German human milk lipids by thin‐layer chromatography and gas chromatography/mass spectrometry

The intake of trans C18:1 as well as of trans hexadecenoic acids (trans C16:1) is believed to be related with numerous physiological disadvantages, such as the risk of coronary heart disease. Since most of the existing data on trans C16:1 contents in human milk fat have been determined without a pre‐separation by thin‐layer chromatography (TLC), the gas chromatographically determined contents of trans C16:1 frequently are too high due to overlaps with C17 fatty acids. Using a highly polar column with a length of 100 m after AgNO₃‐TLC allowed to establish an average content of total trans C16:1 of 0.15 ±0.04% from 39 samples of human milk fat. Moreover, the C16:1 positional isomers trans Δ4, Δ5, Δ6/7, Δ8, Δ9, Δ10, Δ11, Δ12, Δ13 and Δ14 could be quantified from 15 samples exhibiting mean relative contents of 2.6, 3.5, 7.6, 7.2, 24.7, 10.4, 10.1, 14.3, 8.4 and 11.3% related to the total trans C16:1 content, respectively. Also, the C16:1 isomer trans Δ3 could be identified occurring in traces with a mean absolute content of 2 mg/100 g fatty acids. A baseline separation of almost all trans isomers could be achieved for the first time. Further, mass spectrometric analyses of FAME and DMOX derivatives allowed to identify the isomer trans Δ4. Among the C16:1 isomers cis Δ7 to cis Δ14 the isomer cis Δ9 predominated with a relative proportion of 68.3% and an absolute content of 1.88% of all fatty acids. Correspondingly, among the C17:1 isomers cis Δ7 to cis Δ11 the isomer cis Δ9 with 82.6% had the highest relative content.     

Incorporation ofcis- andtrans-octadecenoic acids into the membranes of rat liver mitochondria

The incorporation of dietary isomeric fatty acids into the membranes of liver mitochondria was investigated. Three groups of rats were fed diets containing 3% sunflower seed oil plus 15%, 20%, or 25% partially hydrogenated arachis oil. A fourth group was fed 25% partially hydrogenated arachis oil, but no sunflower seed oil. All diets were given for 3, 6, or 10 weeks. After 10 weeks, the content oftrans fatty acids in the lipids of the mitochondrial membranes was 15–19% of the total fatty acids. The composition of thetrans- and thecis-octadecenoic acids in the lipids of the mitochondrial membranes was similar for all groups supplemented with sunflower seed oil (SO), irrespective of time and dietary level of partially hydrogenated arachis oil (HAO). Thecis 18∶1 (n−8), which was a major isomer of the partially hydrogenated arachis oil, was almost excluded from the mitochondrial fatty acids. Likewise, the content oftrans 18∶1 (n−8) was considerably lower in the mitochondrial lipids than in the diet. On the contrary, the content oftrans 18∶1 (n−6) was higher in the mitochondrial lipids than in the diet. In the group fed without sunflower seed oil, isomers of linoleic acid and arachidonic acid were observed in the lipids of mitochondrial membranes. Presented in part at the ISF Congress, Marseille, September 1976.     

TheTrans-6 fatty acids ofPicramnia sellowii seed oil

The C₁₈ monoenoic acids inPicramnia sellowii Planch. seed oil include bothcis-andtrans-6-octadecenoic acids, as well as oleic acid. The hexadecenoic acids are also thecis- andtrans-Δ6-isomers, and the eicosenoic acids have Δ6-unsaturation of undetermined geometric configuration. The C₁₈ polyenoic acids detected are 9,12- and 6,9-octadecadienoic and 9,12,15- and 6,9,12-octadecatrienoic acids. Partial investigation of another species,P. pentandra Sw., revealed its oil to have a similar fatty acid composition. Presented in part at AOCS Meeting, New York, October 1968. No. Utiliz. Res. Dev. Div., ARS, USDA.     

The effect of conjugated linoleic acid isomers on fatty acid profiles of liver and adipose tissues and their conversion to isomers of 16:2 and 18:3 conjugated fatty acids in rats

Conjugated linoleic acid (CLA) is a collective term that describes different isomers of linoleic acid with conjugated double bonds. Although the main dietary isomer is 9cis,11trans-18∶2, which is present in dairy products and ruminant fat, the biological effects of CLA generally have been studied using mixtures in which the 9cis,11trans- and the 10trans,12cis-18∶2 were present at similar levels. In the present work, we have studied the impact of each isomer (9cis,11trans- and 10trans,12cis-18∶2) given separately in the diet of rats for 6 wk. The 10trans,12cis-18∶2 decreased the triacylglycerol content of the liver (−32%) and increased the 18∶0 content at the expense of 18∶1n−9, suggesting an alteration of the Δ9 desaturase activity, as was already demonstrated in vitro. This was not observed when the 9cis,11trans-18∶2 was given in the diet. Moreover, the 10trans,12cis-18∶2 induced an increase in the C₂₂ polyunsaturated fatty acids in the liver lipids. The 10trans,12cis-18∶2 was mainly metabolized into conjugated 16∶2 and 18∶3, which have been identified. The 9cis,11trans isomer was preferentially metabolized into a conjugated 20∶3 isomer. Thus, the 9cis,11trans- and the 10trans,12cis-CLA isomers are metabolized differently and have distinct effects on the metabolism of polyunsaturated fatty acids in rat liver while altering liver triglyceride levels differentially.