Quantitative analysis for oleic and petroselinic acids in glyceride oils

A rapid quantitative method for the determination of oleic (9-cis-octadecenoic) and petroselinic (6-cis-octadecenoic) acids was required for nutritional research. The methyl esters of these two acids have coincident emergence in GLC separations using polyester columns. A method involving oxidation and GLC analysis of the resultant monocarboxylic acids has been developed. Issued as N.R.C., No. 8813     

A simple and rapid method for concurrent determination of petroselinic and oleic acids in oils

A procedure to determine the petroselinic acid/oleic acid ratio in oils is described. The method is based on transesterification of the constituent fatty acids to methyl esters. An aliquot of the solution of the esters is then analyzed by capillary gas chromatography; another aliquot is used for epoxidation of the double bonds with 3-chloroperoxybenzoic acid and subsequent opening of the oxirane ring with hydrochloric acid to obtain the chlorohydrin derivatives. The hydroxy groups are then silanized, and the reaction mixture is analyzed by high-resolution gas chromatography-mass spectrometry. The procedure is precise, rapid, and reproducible, and several samples can be analyzed in one working day.     

The fatty acid profiles – including petroselinic and cis-vaccenic acid – of different Umbelliferae seed oils

Different varieties of fennel, caraway, and coriander (3 fennel, 7 caraway, and 4 coriander varieties), which belong to the Umbelliferae family, were analyzed on oil and water content, subsequently the fatty acid profiles of the oils were determined by automated gas chromatography. Using fatty acid butyl esters a complete fatty acid profile including petroselinic and cis-vaccenic acid was obtained. Furthermore, the obtained fatty acid contents were compared to those cited in literature, which were determined using different analysis procedures.     

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.     

Separation of petroselinic (cis-6 18:1) and oleic (cis-9 18:1) acids by gas-liquid chromatography of their isopropyl esters

Petroselinic (cis-6 18:1) and oleic (cis-9 18:1) acids that occur together in Umbelliferae seeds can be resolved by gasliquid chromatography (GLC) of their methyl or isopropyl esters on a 50 m × 0.25 mm fused-silica capillary column coated with a 100% cyanopropyl polysiloxane stationary phase (CP Sil 88). The use of isopropyl esters instead of methyl esters increases the difference between equivalent chainlengths from 0.06 carbon unit up to 0.08. This is sufficient to obtain an almost base-line resolution between the two components.cis-Vaccenic acid is completely separated from oleic acid in both derivative forms. GLC of fatty acid isopropyl esters on an appropriate capillary column thus appears to be the simplest means to simultaneously and accurately quantitate petroselinic, oleic andcis-vaccenic acids.     

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     

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.     

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.     

Synthesis of estolides from oleic and saturated fatty acids

Oleic acid and various saturated fatty acids, butyric through stearic, were treated with 0.4 equivalents of perchloric acid at either 45 or 55°C to produce complex estolides. Yields varied between 45 and 65% after Kugelrohr distillation. The estolide number (EN), i.e., the average number of fatty acid units added to a base fatty acid, varied as a function of temperature and saturated fatty acid. The shorter-chain saturated fatty acids, i.e., butyric and hexanoic, provided material with higher degrees of oligomerization (EN=3.31) than stearic acid (EN=1.36). The individual, saturated fatty acid estolides each have very different characteristics, such as color and type of by-products. The higher-temperature reactions occurred at faster rates at the expense of yield, and lactones were the predominant side products. At 55°C, lactone yields increased, but the δ-γ-lactone ratio decreased; this led to lower estolide yields. The opposite trend was observed for the 45°C reaction. The saturate-capped, oleic estolides were then esterified with 2-ethylhexyl alcohol, and the chemical composition of these new estolides remained consistent throughout the course of the reaction.     

Role of oleic acid in the metabolism of essential fatty acids

Groups of young male guinea pigs were fed diets containing corn oil, coconut oil, coconut oil plus elaidic acid, and coconut oil plus oleic acid. The oleic acid-fed group showed signs of essential fatty acid deficiency after four weeks and severe signs after eight weeks. The elaidic acid-fed group did not show these symptoms. It is proposed that oleic acid competes competitively with linoleic acid as a substrate for the enzymes involved in linoleate transformations when only a very limited supply of linoleic acid is available to the animals and oleic acid is made available in relatively large amounts. A detailed analysis of the serum, liver, and adipose tissue lipid and a study of the incorporation of acetate-1-C¹⁴ into different lipids is presented. This paper is based on work supported in part by United States Public Health Grant No. HTS 5306 and by a grant from the Nutrition Foundation Inc., New York.     

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.     

Arylstearic acids from oleic acid. Variables affecting the yield and properties

Summary Twenty-six aromatic compounds were compared in the synthesis of arylstearic acids from oleic acid by the Friedel and Crafts reaction. Xylylstearic acid was the arylstearic acid obtained in the highest yield (92.4%) from technical m-xylene and commerical oleic acid. The various side reactions are disussed including the possible conversion of oleic acid into products which on vacuum distillation of the crude arylstearic acid appear as a forerun and as a still residue. Oleic acid of about 98% purity did not improve the yield but resulted in nearly colorless, rather than yellow viscous oils. Crystalline arylstearic acids have for first time been isolated from the reaction products but only in small yields. Presented at the 39th Annual Meeting of the American Oil Chemists' Society, New Orleans, La., May 4–6, 1948. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration. U. S. Dept. of Agriculture.     

Application of potato lipid acyl hydrolase for the synthesis of monoacylglycerols

Protein extracts from potato tubers contain a lipid acyl hydrolase (LAH) with an unusual selectivity. The component responsible for the enzyme activity is a group of closely related glycoproteins, known as patatin. Potato LAH catalyzes the rapid hydrolysis of monoacylglycerols (MAG), but in contrast expresses only low activity with di- and triacylglycerols. The selectivity of the LAH can be exploited for the synthesis of MAG from fatty acids and glycerol in microaqueous reaction systems. Oleic, linoleic, linolenic, capric, lauric, and myristic acids can be used as reactants, and in each case the reaction products contain >95 mol% MAG and <5 mol% diacylglycerol. By removing water from the reaction mixture by distillation under vacuum, excellent conversions of fatty acids into MAG are possible. Low conversions are observed with palmitic and stearic acids, because of the necessity to use a high temperature (70°C) to maintain a liquid reaction mixture. Potato LAH is rapidly inactivated at 70°C in the microaqueous reaction systems. Potato LAH also catalyzes the selective synthesis of monoesters from oleic acid and simple diols. With oleic acid and diglycerol, monoesters are again the main reaction products, but 17 mol% diesters are also formed.     

The use of nicotinates and sulfoquinovosyl monoacylglycerols in the analysis of monounsaturated n-3 fatty acids by mass spectrometry

Fatty acyl groups (16∶1 and 16∶0) liberated from purified sulfoquinovosyl diacylglycerols produced by the unicellular marine microalga,Heterosigma carterae (formerlyH. akashiwo), were converted to either the corresponding alcohols or methyl esters. Nicotinate derivatives of the alcohols were examined by combined gas chromatography/mass spectrometry, and the methyl esters were examined by nuclear magnetic resonance (NMR) spectroscopy after separation by high-performance liquid chromatography. Three different hexadecenoyl fatty acyl groups were identified, one of which wascis 13-hexadecenoyl (16∶1n−3). Both the configuration and the n−3 position of the double bond in thecis 13-hexadecenoyl moiety were unequivocally established by NMR analysis of the corresponding methyl ester. The nicotinate derived from the alcohol of the 16∶1n−3 fatty acyl moiety gave a characteristic fragmentation series in the electron impact msss spectrum which, by careful interpretation, was consistent with, but not unambiguous for, the assigned location of the double bond. Tandem mass spectrometry experiments on a sulfoquinovosyl monoacylglycerol containing thecis 13-hexadecenoyl group in thesn-2 position, using negative-ion liquid secondary ion mass spectrometry, also gave a fragmentation pattern which was consistent with the positional assignment of the double bond.     

Stepwise purification of fatty acids: compared fractional crystallization with urea or from acetone solutions of palmitoleic,heptadecenoic, and oleic acids

Stepwise partition of a mixture of hexa- (C16:1ω7), hepta-(C17:1ω8), and octadecenoic (C18:1ω9) acids was thoroughly investigated. The efficiency of different rates of three fractionation procedures (i.e., fatty acid crystallization from acetone or fatty acid pared. Fatty acid urea adducts formation is best suited for stepwise removal of the bulk of C18:l (accumulated in the crystals) and C16:l as well as small quantities of C18:l (both being removed in the filtrates). Whatever the technique, high crystallization rates were more efficient.     

Selectivity in incorporation,utilization and retention of oleic and linoleic acids by human skin fibroblasts

Fetal human fibroblasts were grown in culture medium containing 10% fetal bovine serum supplemented with [1-¹⁴C] linoleate or [1-¹⁴C] oleate. At all concentrations of exogenous fatty acids, the incorporation of oleate was greater than that of linoleate. With increased medium fatty acid concentrations, linoleate in triacylglycerol (TAG) could be increased from 13 to 75% of the total incorporated; at each concentration, relatively more linoleate than oleate was in TAG. When the cells were exposed to exogenous oleate/linoleate mixtures, the composition of the mixture determined the extent of incorporation of both fatty acids. When the mixture was primarily linoleate, scarce oleate was used preferentially for phospholipids (PL); no such specificity for scarce linoleate was observed. Addition of exogenous fatty acids resulted in a shift of previously incorporated¹⁴C fatty acids from phospholipid into TAG; retention of oleate in PL was greater than that of linoleate. Incorporation of oleate into phospholipids was also higher than that of linoleate from exogenous fatty acid mixtures which were 80% saturated. It is suggested that normal human fibroblasts have adapted to the low levels of exogenous polyunsaturated fatty acids in culture media by increased use of oleate in phospholipid. Even when the cells aresupplemented with linoleate, the preferential use of oleate in phospholipid groups is retained. Presented in part at the ASBC Meeting, Dallas, april 1979.     

Phenylethyl esters of fatty acids for the analytical resolution of petroselinate and oleate

2-Phenylethyl esters of fatty acids were prepared readily by esterification of free fatty acids or transesterification of other lipids. Compared with methyl esters, phenylethyl esters greatly improve the resolution of oleate and petroselinate by both gas and high-performance liquid chromatography, and the ultraviolet absorption of the phenylethyl esters facilitates detection of the derivatives by high-performance liquid chromatography (HPLC) ultraviolet detectors. The fatty acid compositions of corn and soybean oil obtained by analysis of phenylethyl esters agreed with those obtained with methyl esters. The phenylethyl esters were resolved and eluted on C-18 HPLC columns with much smaller solvent volumes than those reported for other aromatic esters.     

Qualitative and quantitative comparison of minor constituents in different commercial oleic acids

The minor constituents from a high quality commercial oleic acid (SCOA) were isolated and fractionated by liquid column chromatography. They were chemically characterized and their effects on the color stability of oleic acid during heating were determined. The results were compared qualitatively and quantitatively with those from a mixture of commercial oleic acids (MCOA) manufactured by 10 companies. It was found that, qualitatively, SCOA and MCOA contained the same type of minor constituents. However, quantitatively, the MCOA contained 1.18% of minor constituents whereas the SCOA contained only 0.81% of minor constituents. The amount of effective minor constituents which had an adverse effect on the color stability of oleic acid during heating was 0.09% for SCOA vs 0.45% for MCOA. Paper of the Journal Series, New Jersey Agricultural Experiment Station, Cook College, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903