Cis-trans isomerization of oleic,linoleic and linolenic acids

The equilibrium composition ofcis andtrans isomers obtained by isomerizing oleic, linoleic, and linolenic acids with selenium or nitrous acid has been studied using gas chromatography and infrared spectroscopy. The oleic/elaidic equilibrium mixture was found to contain 75–80% elaidic acid instead of the generally accepted 66% value. It is felt that the greater accuracy of gas chromatography and infrared analyses over older methods allows this equilibrium to be defined with greater precision. Similar studies on thecis-trans isomerization of linoleic and linolenic acids indicated that their equilibrium mixtures also contained 75–80%trans double bonds. With linoleic acid, thesetrans bonds were shown to be randomly distributed among the double bonds present. Cis-trans isomerization of linoleic or linolenic acids with selenium produced by-products having elution times equivalent to 18∶2, 18∶1, and 18∶0 on a gas chromatograph. No such by-products were observed when oleic acid was isomerized. Apparently some type of hydrogen-transfer reaction accompanies thecis-trans isomerization of polyunsaturated acids with selenium. Presented at the AOCS meeting in Toronto, Canada, 1962.     

Effect of dietary conjugated linoleic acid (CLA) on metabolism of isotope-labeled oleic,linoleic, and CLA isomers in women

The purpose of this study was to investigate the effect of dietary CLA on accretion of 9c-18∶1, 9c, 12c-18∶2, 10t, 12c-18∶2, and 9c, 11t-18∶2 and conversion of these FA to their desaturated, elongated, and chain-shortened metabolites. The subjects were six healthy adult women who had consumed normal diets supplemented with 6 g/d of sunflower oil or 3.9 g/d of CLA for 63 d. A mixture of 10t, 12c-18∶2-d ₄, 9c, 11t-18∶2-d ₆, 9c-18∶1-d ₈, and 9c, 12c-18∶2-d ₂, as their ethyl esters, was fed to each subject, and nine blood samples were drawn over a 48-h period. The results show that dietary CLA supplementation had no effect on the metabolism of the deuterium-labeled FA. These metabolic results were consistent with the general lack of a CLA diet effect on a variety of physiological responses previously reported for these women. The ²H-CLA isomers were metabolically different. The relative percent differences between the accumulation of 9c, 11t-18∶2-d ₆ and 10t, 12c-18∶2-d ₄ in plasma lipid classes ranged from 9 to 73%. The largest differences were a fourfold higher incorporation of 10t, 12c-18∶2-d ₄ than 9c, 11t-18∶2-d ₆ in 1-acyl PC and a two- to threefold higher incorporation of 9c, 11t-18∶2-d ₆ than 10t, 12c-18∶2-d ₄ in cholesterol esters. Compared to 9c-18∶1-d ₈ and 9c, 12c-18∶2-d ₂, the 10t, 12c-18∶2-d ₄ and 9c, 11t-18∶2-d ₆ isomers were 20–25% less well absorbed. Relative to 9c-18∶1, incorporation of the CLA isomers into 2-acyl PC and cholesterol ester was 39–84% lower and incorporation of 10t, 12c-18∶2 was 50% higher in 1-acyl PC. This pattern of selective incorporation and discrimination is similar to the pattern generally observed for trans and cis 18∶1 positional isomers. Elongated and desaturated CLA metabolites were detected. The concentration of 6c, 10t, 12c-18∶3-d ₄ in plasma TG was equal to 6.8% of the 10t, 12c-18∶2-d ₄ present, and TG was the only lipid fraction that contained a CLA metabolite present at concentrations sufficient for reliable quantification. In conclusion, no effect of dietary CLA was observed, absorption of CLA was less than that of 9c-18∶1, CLA positional isomers were metabolically different, and conversion of CLA isomers to desaturated and elongated metabolites was low.     

Effect of dietary arachidonic acid on metabolism of deuterated linoleic acid by adult male subjects

The influence of dietary supplementation with 20:4n−6 on uptake and turnover of deuterium-labeled linoleic acid (18:2n−6[d ₂]) in human plasma lipids and the synthesis of desaturated and elongated n−6 fatty acids from 18:2n−6[d ₂] were investigated in six adult male subjects. The subjects were fed either a high-arachidonic acid (HIAA) diet containing 1.7 g/d or a low-AA (LOAA) diet containing 0.21 g/d of AA for 50 d. Each subject was then dosed with about 3.5 g of 18:2n−6[d ₂] as the triglyceride (TG) at 8:00 a.m., 12:00, and 5:00 p.m. The total 18:2n−6[d ₂] fed to each subject was about 10.4 g and is approximately equal to one-half of the daily intake of 18:2n−6 in a typical U.S. male diet. Nine blood samples were drawn over a 96-h period. Methyl esters of plasma total lipid (TL), TG, phospholipid, and cholesterol ester were analyzed by gas chromatography-mass spectroscopy. Dietary 20:4n−6 supplementation did not affect uptake of 18:2n−6[d ₂] in plasma lipid classes over the 4-d study period nor the estimated half-life of 24–36 h for 18:2n−6[d ₂]. The percentages of major deuterium-labeled desaturation and elongation products in plasma TL, as a percentage of total deuterated fatty acids, were 1.35 and 1.34% 18:3n−6[d ₂]; 0.53 and 0.50% 20:2n−6[d ₂]; 1.80 and 0.92% 20:3n−6[d ₂] and 3.13 and 1.51% 20:4n−6[d ₂] for the LOAA and HIAA diet groups, respectively. Trace amounts (<0.1%) of the TL concentration data for both 20:3n−6[d ₂] and 20:4n−6[d ₂] were 48% lower (P<0.05) in samples from the HIAA diet group than in samples from the LOAA diet group. For a normal adult male consuming a typical U.S. diet, the estiamted accumulation in plasma TL of 20:4n−6 synthesized from 20 g/d (68 mmole) of 18:2n−6 is 677 mg/d (2.13 mmole). Dietary supplementation with 1.5 g/d of 20:4n−6 reduced accumulation of 20:4n−6 synthesized from 20 g/d of 18:2n−6 to about 326 mg/d (1.03 mmole).     

The melting points of binary mixtures of oleic,linoleic, and linolenic acids

Summary 1. The melting points of binary mixtures of oleic, linoleic, and linolenic acids have been reported. 2. The oleic-linoleic acid system has eutectics for the α and β forms of oleic acid of 75.2 and 76.3 mole per cent linoleic acid, at −10.0° and −9.8°, respectively. 3. Linoleic and linolenic acid mixtures show only melting points intermediate between the pure acids. 4. The oleic-linolenic acid system has eutectics for the α and β forms of oleic acid of 82.7 and 85.5 mole per cent linolenic acid, at −15.7° and −15.1°, respectively. A cooperative organization participated in by the Bureaus of Agricultural Chemistry and Engineering and Plant Industry of the U. S. Department of Agriculture, and the Agricultural Experiment Stations of the North Central States of Illinois. Indiana, Iowa, Kansas. Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin.     

The thiocyanogen values of the methyl esters of oleic,linoleic, and linolenic acids

Summary Thiocyanogen values were determined on the methyl esters of oleic, linoleic and linolenic acids and on six different mixtures of these esters, using 0.1 and 0.2 normal thiocyanogen solutions. The values determined with 0.1 N solutions showed less variation than those determined with 0.2 N. The composition of the mixtures calculated from equations based on the found thiocyanogen values of the esters agreed with the known composition within reasonable limits. Comparisons were made with the composition calculated with the Kaufmann-theory values. It is suggested that the F.A.C. consider adopting tentatively the values 89.4 for oleic acid, 93.9 for linoleic acid, and 162.0 for linolenic acid when 0.1 N thiocyanogen solutions are used; the values 89.4, 96.8, and 167.5 when 0.2 N solutions are employed. These represent the average of the values for these acids which have been reported in the literature. Agricultural Chemical Research Division Contribution No. 15     

The α,β-distribution of oleic,linoleic and linolenic acids in cruciferae seed triglycerides

Correlation studies on lipolysis data from 24 species of Cruciferae seed triglycerides have revealed very regular positional distribution patterns for oleic, linoleic and linolenic acids. When the ratio % 18:1 in β-position/% 18:1 in total triglycerides for each species is plotted vs. the content of Category I acids (16:0, 18:0, plus all C₂₀, C₂₂ and C₂₄ acids) in the total triglycerides, a smooth curve is obtained. Application of suitable statistical procedures yields a best-fitting curve, from which an equation expressing the % 18:1 in the β-position as a function of the fatty acid composition of the total triglycerides can be derived. The % 18:1 in the α-position is then readily calculated by difference. Similar distinctive relationships have also been developed for linoleic and linolenic acids. Comparison of calculated and experimental results shows that the relationships developed here are considerably more accurate than the previous Gunstone-Mattson and Evans hypotheses for estimating the α,β-distributions of 18:1, 18:2 and 18:3 in Cruciferae seed triglycerides. Presented in part at the AOCS meeting in San Francisco, California, April 1969.     

The activating effect of dietary protein on linoleic acid desaturation

The desaturation of¹⁴C-1-linoleic acid to γ-linolenic acid and their incorporation into the microsomal lipids of rats fed on a balanced diet and a protein diet were measured in vitro. It was shown that a protein diet does not change significantly the distribution of the radioactivity among the different lipidic fractions compared to the animals fed on a balanced diet. However the microsomal desaturation of linoleic acid to γ-linolenic acid increased in the rats maintained on a protein diet. Besides, the amount and composition of the free fatty acids present in the microsomes of the animals fed on both diets were similar enough to discard the hypothesis that they may modify the desaturation of linoleic acid produced by the diet. The enzymic activity of the linoleyl desaturase of liver microsomes of animals fed on a protein diet, measured in substrate saturating conditions, is greater than in animals with balanced diet. Consequently the results support the hypothesis that a protein diet increases specifically the desaturating activity of the microsomes.     

Effect of triacylglycerol structure on absorption and metabolism of isotope-labeled palmitic and linoleic acids by humans

The effect of dietary TAG structure and fatty acid acyl TAG position on palmitic and linoleic acid metabolism was investigated in four middle-aged male subjects. The study design consisted of feeding diets containing 61 g/d of native lard (NL) or randomized lard (RL) for 28 d. Subjects then received an oral dose of either 1,3-tetradeuteriopalmitoyl-2-dideuteriolinoleoyl-rac-glycerol or a mixture of 1,3-dideuteriolinoleoyl-2-tetradeuteriopalmitoyl-rac-glycerol and 1,3-hexadeuteriopalmitoyl-2-tetradeuteriolinoleoyl-rac-glycerol. Methyl esters of plasma lipids isolated from blood samples drawn over a 2-d period were analyzed by GC-MS. Results showed that absorption of the ²H-fatty acids (²H-FA) was not influenced by TAG position. The ²H-FA at the 2-acyl TAG position were 85±4.6% retained after absorption. Substantial migration of ²H-16∶0 (31.2±8.6%) from the sn-2 TAG position to the sn-1,3 position and ²H-18∶2n−6 (52.8±6.4%) from the sn-1,3 position to the sn-2 position of chylomicron TAG occurred after initial absorption and indicates the presence of a previously unrecognized isomerization mechanism. Incorporation and turnover of the ²H-FA in chylomicron TAG, plasma TAG, and plasma cholesterol esters were not influenced by TAG acyl position. Accretion of ²H-16∶0 from the sn-2 TAG position in 1-acylphosphatidylcholine was 1.7 times higher than ²H-16∶0 from the sn-1,3 TAG positions. Acyl TAG position did not influence ²H-18∶2n−6 incorporation in PC. The concentration of ²H-18∶2n−6-derived ²H-20∶4n−6 in plasma PC from subjects fed, the RL diet was 1.5 times higher than for subjects fed the NL diet, and this result suggests that diets containing 16∶0 located at the sn-2 TAG position may inhibit 20∶4n−6 synthesis. The overall conclusion is that selective rearrangement of chylomicron TAG structures diminishes but does not totally eliminate the metabolic and physiological effects of dietary TAG structure.     

Effect of dietary linolenic acid and docosahexaenoic acid on growth and fatty acid composition of rainbow trout (Salmo gairdneri)

Methyl linolenate 18∶3ω3 and docosahexaenoate 22∶6ω3 were incorporated in semipurified diets at several levels and fed to trout previously maintained on a fat-free diet. After 14 weeks, the weight gain and feed conversion of the fish on each diet were determined. The fatty acid composition of the lipid from each group of fish was analyzed by gas liquid chromatography. Both 18∶3ω3 and 22∶6ω3 fed at the 1% level supported maximum growth of the fish. The control group, which were fed no ω3 fatty acids, exhibited a shock syndrome, poor appetite and a very slow growth rate. Tissue fatty acid analysis revealed eicosatrienoic acid 20∶3ω9 accumulated in the phospholipid fraction of this group. The 20∶3ω9 level was lowered when either 18∶3ω3 or 22∶6ω3 was included in the diet. Analysis showed that the dietary 18∶3ω3 was rapidly converted by the fish into 22∶6ω3 with a high concentration in the phospholipid. However 22∶6ω3 fed to the fish remained unchanged and little or no retroconversion of this fatty acid was observed. Presented in part at the AOCS Meeting, Atlantic City, October 1971. Technical paper no. 3247, Oregon Agricultural Experiment Station.     

Analysis of novel hydroperoxides and other metabolites of oleic, linoleic, and linolenic acids by liquid chromatography-mass spectrometry with ion trap MSn

Linoleate is oxygenated by manganese-lipoxygenase (Mn-LO) to 11S-hydroperoxylinoleic acid and 13R-hydroperoxyoctadeca-9Z,11E-dienoic acid, whereas linoleate diol synthase (LDS) converts linoleate sequentially to 8R-hydroperoxylinoleate, through an 8-dioxygenase by insertion of molecular oxygen, and to 7S,8S-dihydroxylinoleate, through a hydroperoxide isomerase by intramolecular oxygen transfer. We have used liquid chromatography-mass spectrometry (LC-MS) with an ion trap mass spectrometer to study the MSⁿ mass spectra of the main metabolites of oleic, linoleic, α-linolenic and γ-linolenic acids, which are formed by Mn-LO and by LDS. The enzymes were purified from the culture broth (Mn-LO) and mycelium (LDS) of the fungus Gaeumannomyces graminis. MS³ analysis of hydroperoxides and MS² analysis of dihydroxy- and monohydroxy metabolites yielded many fragments with information on the position of oxygenated carbons. Mn-LO oxygenated C-11 and C-13 of 18∶2n−6, 18∶3n−3, and 18∶3n−6 in a ratio of ∼1∶1–3 at high substrate concentrations. 8-Hydroxy-9(10)expoxystearate was identified as a novel metabolite of LDS and oleic acid by LC-MS and by gas chromatography-MS. We conclude that LC-MS with MSⁿ is a convenient tool for detection and identification of hydroperoxy fatty acids and other metabolites of these enzymes.     

Preparation of hydroxy acids by sulfation of oleic and linoleic acids

Summary Monohydroxystearic acids were prepared by sulfation and subsequent hydrolysis of oleic acid, and the effect of reaction conditions on yield was studied. Monohydroxystearic acids were obtained from commercial oleic acid in 72% yield and from pure oleic acid in 86% yield. Conditions for the best yields apparently gave increased amounts of isomeric hydroxy acids. Hydroxy acids prepared by the sulfation and subsequent hydrolysis of linoleic acid were converted to methyl esters, and purified by fractional distillation and low temperature crystallization. Experimental evidence indicates that sulfuric acid reacts with one double bond of linoleic acid to form isomeric monohydroxyoleic acids and with both double bonds to form dihydroxystearic acids. The by-products formed by the sulfation of linoleic acid include both ester-type polymers and additional polymeric material which cannot be converted to monomers by alkaline saponification. When commercial oleic acid is sulfated and subsequently hydrolyzed, the monohydroxystearic acid thus obtained presumably contains monohydroxyoleic acids and dihydroxystearic acids resulting from the linoleic acid present in the starting material. The formation of an unsaponifiable polymer during the sulfation of linoleic acid accounts in part for the lower yield of hydroxy acids obtained from commercial oleic acid, as compared with that of purified oleic acid. One of the laboratories of the Bureau of Agricultural and Industrial Ohemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Spectral properties of linoleic and linolenic acids prepared by debromination

Summary Modified procedures are described for the preparation of linoleic and linolenic acids which remove and/or prevent the formation of conjugated acids. The importance of spectrophotometric measurements as a criterion of purity is emphasized. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Effect of catecholamines and β-blockers on linoleic acid desaturation activity

The effect of catecholamines and adrenergic blocking agents on the oxidative desaturation of linoleic acid in rat liver microsomes was studied. Epinephrine (1 mg/kg/body weight) produced a significant decrease on the conversion of [1-¹⁴C]linoleic acid to γ-linolenic acid. The effect of epinephrine was blocked by single injections of the β blockers propranolol (10 mg/kg body weight) or dichloroisoproterenol 30 min before the hormone treatment. Isoproterenol (100 μg/kg body weight) produced a significant decrease on the activity of the linoleyl-CoA desaturase. The effect of the catecholamines was postulated to be mediated through β receptors by an enhancement of the intracellular levels of cyclic AMP.     

Effects of dietary proteins on linoleic acid desaturation and membrane fluidity in rat liver microsomes

The effect of dietary protein, casein (CAS) and soybean protein (SOY), on linoleic acid desaturation in liver microsomes was studied in rats. The activity of Δ6 desaturase in total and rough endoplasmic reticula (ER and RER) was significantly higher in the CAS group than in the SOY group. In ER and smooth endoplasmic reticulum, the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene, when incorporated into the membrane, was decreased in the SOY group and accompanied by a reduction in the cholesterol/phospholipid (CHOL/PL) ratio, consistent with an increase in membrane fluidity. In a separate study, the effect of varying dietary proteins, CAS, milk whey protein, egg albumin, SOY, potato protein and wheat gluten, on the relationship between the Δ6 desaturase activity and microsomal membrane fluidity was also examined. The results indicated that the dietary protein-dependent change in the liver microsomal CHOL/PL ratio affected membrane fluidity, and subsequently the activity of Δ6 desaturase in liver microsomes. However, since dietary protein influenced the Δ6 desaturase activity in RER without influencing membrane fluidity, it is possible that some regulation might have taken place at the level of enzyme synthesis.     

Separation of the methyl esters of oleic,linoleic, and linolenic acids by column chromatography using cation exchange resin containing silver ion

By taking advantage of the tendency of silver ion to form complexes with unsaturated compounds, the methyl esters of oleic, linoleic, and linolenic acids have been cleanly separated in good yield by column chromatography. The silver ion was supported by means of a cation exchange resin; no silver was ever eluted from the column. Aqueous methanol, pure methanol, and ethanol saturated with butene-1 were employed as solvents.     

Variability of linolenic and linoleic acids in soybean oil

Summary Soybean oil from all locations and varieties of Uniform Test Groups II, III, and IV have been analyzed for linolenic and linoleic acid by an improved spectrophotometric method. Location composites in Group II varied from 5.9% to 8.3% in linolenic acid and from 45.3% to 50.4% in linoleic. Variety composites varied from 5.4% to 8.0% in linolenic and from 43.9% to 51.6% in linoleic. The location variability was shown to be closely associated with maximum temperature during seed development. Temperature appears to be the most important environmental factor affecting these acids, especially linolenic. The percentages of the two acids are positively correlated with each other. Publication No. 291 of the U. S. Regional Soybean Laboratory, Urbana, Ill.     

Effect of dietary linolenic and linoleic acids upon growth and lipid metabolism of rainbow trout (Salmo gairdneri)

Nine diets, each containing different levels of linoleic acid (18∶2ω6) and linolenic (18∶3ω3) were fed to duplicate groups of rainbow trout for 14 weeks. The growth rate, feed efficiency, accumulated mortality, and fatty acid composition of neutral fat and phospholipids of these groups of fish were determined. The growth was slow in the groups of fish receiving diets containing (A) low concentration of 18∶3ω3 and (B) high concentration (5%) of 18∶2ω6. The accumulated mortality was high in these groups of fish. The diet containing 1% 18∶3ω3 alone supported rapid fish growth with low mortality. The feed efficiency of this diet was also high. The metabolism of 18∶2ω6 and 18∶3ω3 in fish and their conversion to more unsaturated fatty acids typical of fish lipids was investigated.     

捕收剂的亚油酸/油酸比值对磷矿浮选的影响

探讨了几种脂肪酸皂类捕收剂的亚油酸/油酸(L)值对浮选温度和选别指标的影响。黄麦岭磷矿的浮选试 验表明,L值越大。综合指数K越高,选矿效果越好。温度较低时,应选用亚油酸含量较高的脂肪酸皂捕收剂。     

Separation of oleic acid and linoleic acid by solvent extraction

Oleic acid and linoleic acid were separated by extraction with the solvent systemn-heptane-dimethyl sulfoxide. The separation factor decreased with increasing concentrations of fatty acids in the dimethyl sulfoxide (DMSO) layer. At fatty concn of 0.60 and 16.02%, the separation factors of linoleic acid were found to be 2.18 and 1.28, respectively. The solvent could be removed by adding water to the extract. DMSO is very soluble in water while the fatty acids are only sparingly soluble. Thus DMSO and fatty acids are separated. A phase diagram for the system Unitol ACD-DMSO-water at 25C and 1 atm is given.