Analysis of hydroxylated fatty acids from plant oils

A novel process has been described recently for the preparation of hydroxylated fatty acids (HOFA) and HOFA methyl esters from plant oils. HOFA methyl esters prepared from conventional and alternative plant oils were characterized by various chromatographic methods (thin-layer chromatography, high-performance liquid chromatography, and gas chromatography) and gas chromatography-mass spectrometry as well as¹H and¹³C nuclear magnetic resonance spectroscopy. HOFA methyl esters obtained fromEuphorbia lathyris seed oil, low-erucic acid rapeseed oil, and sunflower oil contain as major constituents methylthreo-9,10-dihydroxy octadecanoate (derived from oleic acid) and methyl dihydroxy tetrahydrofuran octadecanoates, e.g., methyl 9,12-dihydroxy-10,13-epoxy octadecanoates and methyl 10,13-dihydroxy-9,12-epoxy octadecanoates (derived from linoleic acid). Other constituents detected in the products include methyl esters of saturated fatty acids (not epoxidized/derivatized) and traces of methyl esters of epoxy fatty acids (not hydrolyzed). The products that contain high levels of monomeric HOFA may find wide application in a variety of technical products.     

The effect of fatty acid composition on the acrylation kinetics of epoxidized triacylglycerols

Epoxidized oils, epoxidized triacylglycerols, and epoxidized fatty acid methyl esters were made by reaction with performic acid formed in situ. The extent of epoxidation was ca. 95% for all of the epoxidized samples, as determined by ¹H nuclear magnetic resonance. The epoxidized samples were reacted with an excess of acrylic acid for different reaction times. The acrylation reaction was found to have a first-order dependence on the epoxide concentration for all oils, pure triacylglycerols, and fatty acid methyl esters. However, the rate constant of acrylation was found to depend on the composition of the epoxidized material. The acrylation rate constant for 9,10-epoxystearic acid was 96 L²/(mol²·min). The rate constant of acrylation for the epoxides on 9,10,12,13-diepoxystearic acid was 60 L²/(mol²·min). The acrylation rate constant for the epoxides on 9,10,12,13,15,16-triepoxystearic acid was 50 L²/(mol²·min). Thus, the rate constant of acrylation increased as the number of epoxides per fotty acid decreased. Multiple epoxides per fatty acid decrease the reactivity of the epoxides because of steric hindrance effects, and the oxonium ion, formed as an intermediate during the epoxyacrylic acid reaction, is stabilized by local epoxide groups. These results were used to derive an acrylation kinetic model that predicts rate constants from fatty acid distributions in the oil. The predictions of the model closely match the experimentally determined rate constants.     

Fatty acids of Thespesia populnea: Mass spectrometry of picolinyl esters of cyclopropene fatty acids

Thespesia populnea belongs to the plant family of Malvaceae which contain cyclopropane and cyclopropene fatty acids. However, previous literature reports vary regarding the content of these compounds in Thespesia populnea seed oil. In this work, the content of malvalic acid (8,9‐methylene‐9‐heptadecenoic acid) in the fatty acid profile of Thespesia populnea seed oil was approximately 7% by GC. Two cyclopropane fatty acids were identified, including dihydrosterculic acid. The methyl and picolinyl esters of Thespesia populnea seed oil were also prepared. The mass spectrum of picolinyl malvalate was more closely investigated, especially an ion at m/e 279, which does not fit the typical series of ions observed in picolinyl esters. It is shown that this ion is caused by cleavage at the picolinyl moiety and contains the fatty acid chain without the picolinyl moiety. This type of cleavage has previously not been observed prominently in picolinyl esters and may therefore be diagnostic for picolinyl esters of cyclopropene fatty acids. The NMR spectra of Thespesia populnea methyl esters are also discussed. Practical applications: The work reports the fatty acid composition of Thespesia seed oil whose derivatives have not yet been extensively utilized for industrial purposes, for example, biodiesel. Knowing this composition is essential for understanding potential uses and, for example, in case of biodiesel the fuel properties. Besides this issue, some data (mass spectrometry and NMR) crucial for obtaining the composition information are analyzed in detail. The biodiesel properties of methyl esters of Thespesia populnea will be reported separately.     

Epoxidation ofLesquerella andLimnanthes (Meadowfoam) oils

Lesquerella gordonii (Gray) Wats andLimnanthes alba Benth. (Meadowfoam) are species being studied as new and alternative crops. Triglyceride oil from lesquerella contains 55–60% of the uncommon 14-hydroxy-cis-11-eicosenoic acid. Meadowfoam oil has 95% uncommon acids, includingca. 60%cis-5-eicosenoic acid. Both oils are predominantly unsaturated (3% saturated acids), and have similar iodine values (90–91), from which oxirane values of 5.7% are possible for the fully epoxidized oils. Each oil was epoxidized withm-chloro-peroxybenzoic acid, and oxirane values were 5.0% (lesquerella) and 5.2% (meadowfoam). The epoxy acid composition of each product was examined by gas chromatography of the methyl esters, which showed that epoxidizedL. gordonii oil contained 55% 11,12-epoxy-14-hydroxyeicosanoic acid, and epoxidized meadowfoam oil contained 63% 5,6-epoxyeicosanoic acid, as expected for normal complete epoxidation. Mass spectrometry of trimethylsilyloxy derivatives of polyols, prepared from the epoxidized esters, confirmed the identity of the epoxidation products and the straightforward nature of the epoxidation process. Synthesis and characterization of these interesting epoxy oils and derivatives are discussed.     

Methyl Esters (Biodiesel) from and Fatty Acid Profile of Gliricidia sepium Seed Oil

Increasing the supply of biodiesel by defining and developing additional feedstocks is important to overcome the still limited amounts available of this alternative fuel. In this connection, the methyl esters of the seed oil of Gliricidia sepium were synthesized and the significant fuel‐related properties were determined. The fatty acid profile was also determined with saturated fatty acids comprising slightly more than 35 %, 16.5 % palmitic, 14.5 % stearic, as well as lesser amounts of even longer‐chain fatty acids. Linoleic acid is the most prominent acid at about 49 %. Corresponding to the high content of saturated fatty acid methyl esters, cold flow is the most problematic property as shown by a high cloud point of slightly >20 °C. Otherwise, the properties of G. sepium methyl esters are acceptable for biodiesel use when comparing them to specifications in biodiesel standards but the problematic cold flow properties would need to be observed. The ¹H‐ and ¹³C‐NMR spectra of G. sepium methyl esters are reported.     

Chemical Composition and Characteristics of <Emphasis Type="Italic">Commiphora wightii</Emphasis> (Arnott) Bhandari Seed Oil

The seeds of Commiphora wightii (Arnott) Bhandari contain 9.8 ± 0.7% oil. The fatty acid composition and chemical properties of the extracted oil were determined. Gas liquid chromatography of the methyl esters of the fatty acids shows the presence of 46.62% saturated fatty acids and 51.40% unsaturated fatty acids. The fatty acid composition is as follows: capric acid 3.50%, myristic acid 14.51%, palmitic acid 6.68%, stearic acid 4.70%, arachidic acid 3.18%, behenic acid 14.05%, myristoleic acid 1.34%, palmitoleic acid 12.07%, oleic acid 14.15%, eicosenoic acid 0.11%, linoleic acid 22.34% and alpha linoleic acid 1.37%.     

Liquid–Liquid Equilibrium for Systems Containing Epoxidized Oils,Formic Acid,and Water: Experimental and Modeling

Epoxidized oils are eco-friendly plasticizers, which are industrially produced through the epoxidation reaction in a formic acid-hydrogen peroxide autocatalyzed system. The fundamental knowledge to describe the phase equilibrium of systems after epoxidation reaction is lacking, which is crucial for the design of the purification facilities. This work reported experimental data for the liquid–liquid equilibrium of three systems, i.e., epoxidized fatty acid methyl esters + formic acid + water, epoxidized fatty acid 2-ethylhexyl esters + formic acid + water, and epoxidized soybean oil + formic acid + water, in the temperature range (303.15–348.15) K under atmospheric pressure. The results indicated that the liquid–liquid equilibrium constant of formic acid in the systems followed the order of epoxidized fatty acid 2-ethylhexyl esters > epoxidized fatty acid methyl esters > epoxidized soybean oil. Moreover, the obtained experimental data were correlated using nonrandom two liquid (NRTL) and universal quasi chemical (UNIQUAC) models. The maximum root mean square deviation (RMSD) values as low as 0.0052 and 0.0263 were estimated using the NRTL and UNIQUAC model, respectively. The NRTL model is more suitable than the UNIQUAC model to describe the liquid–liquid equilibrium behavior of these ternary systems.     

Einfluß von Licht und Tocopherolgehalt auf die Oxidationsstabilität von Fettsäuremethylestern

Influence of light and contents of tocopherols on the oxidative stability of fatty acid methyl esters The oxidative stability of different plant oil based fatty acid methyl esters can be estimated by determining the induction period with the active oxygen method. Measuring the volatile and oil soluble acids for a long period preceding the induction period shows that the values are approaching a certain limit. Even if the esters do not differ dramatically in the composition of fatty acids it is a fact that the different production processes influence the amount of tocopherols significantly. The exclusion of light is more crucial than the exclusion of air when storing plant oil based fatty acid esters.     

Evaluation of nonpolar methyl esters by column and gas chromatography for the assessment of used frying olive oils

The measurement of unaltered methyl esters separated from polar methyl esters by column chromatog-raphy was used to evaluate the alteration of an olive oil that had been used 15 times to fry potatoes. Unaltered methyl ester (the nonpolar fraction) decreased significantly (94.9 ± 0.8%vs 98.2 + 0.5%; p < 0.05), while the polar fraction increased significantly (4.0 ± 0.7%vs 2.1 ± 0.7%; p < 0.05) after 15 fryings. The unrecoverable fraction also increased. In order to avoid column contamination the gas Chromatographic analysis was only done on the nonpolar fractions. Linoleic and oleic acids showed a tendency to decrease while saturated fatty acid tended to increase. The unsaturated/saturated fatty acids ratio decreased from an initial value of 7.05 to 6.40 in the last frying. Quantitative gas Chromatographic analysis using both the percentage fatty acid composition and the relative amount of unaltered methyl esters showed a significant oleic acid decrease after 15 fryings (75.8 ± 0.6vs 78.9 ± 0.2 mg/100 mg oil; p < 0.05). To whom correspondence should be addressed     

Chemical epoxidation of a natural unsaturated epoxy seed oil fromVernonia galamensis and a look at epoxy oil markets

Since 1963, production of all epoxy esters has ranged from 60 to 150 million lb annually, a steady 7% of the 1 to 2 billion lb of annual plasticizer production. Growth rates in production averaged 4.3% for all plasticizers, 3.8% for all epoxy esters and 5.0% for epoxidized soybean oil (ESBO). ESBO accounted for 70–76% of total epoxy ester production (1963–1982). The natural liquid epoxy oil fromVernonia galamensis seed, with oxirane value (4.1%) and viscosity (100 cps) similar to some commercial epoxy fatty esters but with molecular weight similar to epoxidized vegetable oils, combines some of the properties of both commercial types. Chemical epoxidation ofVernonia oil raises the oxirane content to 8.2, intermediate between ESBO and epoxidized linseed oil (ELSO), while consuming less of the costly epoxidizing reagents. Epoxidation proceeds in stepwise fashion through partially epoxidized products, which are converted to final product. Since the major fatty components ofVernonia oil arecis-12,13-epoxy-9-octadecenoic (75%) and linoleic (13%) acids, further epoxidation produces fatty acids that are specifically epoxidized at the 9,10- and 12,13-positions, and the major product has 6 epoxy units per triglyceride molecule. The resulting mixture of products has compositional and physical properties distinctly different from commercial samples of ESBO and ELSO.     

Identification of α-parinaric acid in the seed oil ofSebastiana brasiliensis sprengel (Euphorbiaceae)

Besides some usual fatty acids, the seed oil ofSabastiana brasiliensis (Euphorbiaceae) contains up to 39% (estimated by ultraviolet spectroscopy) of α-parinaric acid (cis, trans, trans, cis-9, 11, 13, 15-octadecatetraenoic acid). The fatty acids were analyzed by gas chromatography and gas chromatography/mass spectrometry as their methyl esters. The structure of α-parinaric acid was proven by a combination of chemical and spectroscopic methods, conducted with the crude oil, the methyl ester mixture, and the isolated fatty acid methyl ester. Complete assignment of the¹H and¹³C nuclear magnetic resonance (NMR) shifts of α-parinaric acid was carried out by two-dimensional NMR experiments Presented in part at the 21st world Congress and Exhibition of the International Society for Fat Research (ISF), October 1–6, 1995, The Hague, The Netherlands.     

Analysis of epoxidized soybean oil by gas chromatography

A fast and cost-effective procedure to quantitate epoxidized soybean oil by means of an external standard method is reported. This procedure is applicable to commercial epoxidized oils, polymer additive packages and polymers—polyvinyl chloride (PVC)—containing epoxidized oils. The epoxidized soybean oil is converted into fatty acid methyl esters with tetramethylammonium hydroxide, and analyzed by capillary gas chromatography with flame-ionization detection. In PVC samples, the epoxidized soybean oil was extracted with toluene and followed by derivatization prior to analysis. The methyl esters of monoepoxyoctadecanoic, diepoxyoctadecanoic and triepoxyoctadecanoic acid were separated with a short capillary column.     

Curupira tefeensis (Olacaceae) — A Rich Source of Very Long Chain Fatty Acids

The fatty acid composition of the seed oil of Curupira tefeensis was analysed by capillary GC of their methyl esters. The gaschromatographic assignments were ensured by corresponding mass spectra. The oil is composed to more than 62% of very long chain fatty acids (>C18). Erucic acid is found to be the main component (35%). The position of the double bonds of the monounsaturated fatty acids (MUFAME) was verified after derivatization with dimethyl disulfide and subsequent GC/MS analysis. All identified MUFAME belong to the (n-9-)type. The UV-spectroscopical data show that approx. 1.2% conjugated acetylenic fatty acids occur in the oil. Furthermore IR- and NMR-spectroscopical investigations and the basic analyses of the seed were carried out.     

Identification of nine acetylenic fatty acids, 9-hydroxystearic acid and 9,10-epoxystearic acid in the seed oil ofJodina rhombifolia hook et arn. (Santalaceae)

In addition to some usual fatty acids, the seed oil ofJodina rhombifolia (Santalaceae) contains nine acetylenic fatty acids [9-octadecynoic acid (stearolic acid) (1.1%),trans-10-heptadecen-8-ynoic acid (pyrulic acid) (20.1%), 7-hydroxy-trans-10-heptadecen-8-ynoic acid (2.3%),trans-10,16-heptadecadien-8-ynoic acid (0.7%), 7-hydroxy-trans-10,16-heptadecadien-8-ynoic acid (0.1%),trans-11-octadecen-9-ynoic acid (ximenynic acid) (20.3%), 8-hydroxy-trans-11-octadecen-9-ynoic acid (12.2%),trans-11,17-octadecadien-9-ynoic acid (1.5%), 8-hydroxy-trans-11,17-octadecadien-9-ynoic acid (1.3%), 9-hydroxystearic acid (<0.1%) and 9,10-epoxystearic acid (0.7%)]. The fatty acids have been analyzed by gas chromatography/mass spectrometry of their methyl ester and 4,4-dimethyloxazoline derivatives. The hydroxy fatty acid methyl esters have been examined also as trimethyl-silyl ethers. Furthermore, the fatty acid methyl esters (FAME) have been fractionated according to their polarity (FAME-A: nonhydroxy; FAME-B: hydroxy fatty acids) and to their degree of unsaturation (FAME-A1/A2; FAME-B1/B2) by preparative thin-layer chromatography and argentation chromatography, respectively. All of these fractions have been analyzed by ultraviolet and infrared spectroscopy, and the fractions FAME-A and FAME-B have been analyzed further by nuclear magnetic resonance (¹H,¹³C, 2D H/C, attached proton test) spectroscopy and gas chromatography/mass spectrometry. This work is dedicated to the 65th birthday of Prof. Dr. K. Pfeilsticker, Institut of Food Science, University Bonn (Germany).     

Antioxidant effect of mono‐ and dihydroxyphenols in sunflower oil with different levels of naturally present tocopherols

Antioxidant properties of mono‐ and dihydroxyphenolic acids and their alkyl esters were examined, with emphasis on the relationship between their molecular structure and antioxidant activity. Test media with different tocopherol level were used for determining the oxidative stability: original refined sunflower oil (total tocopherols 149.0 mg/kg), partially tocopherol‐stripped sunflower oil (total tocopherols 8.7 mg/kg) and distilled fatty acid methyl esters (FAME) as a tocopherol‐free medium. The chemical reaction of tocopherols with diazomethane tested for the purpose to eliminate their antioxidant activity failed due to the negligible degree of methylation of hydroxyl group in the tocopherol molecule. Caffeic acid and protocatechuic acid (3,4‐dihydroxyphenolic acids) and their alkyl esters were found to be more active antioxidants than monohydroxyphenolic acid (p‐hydroxybenzoic acid), 2,5‐dihydroxyphenolic acid (gentisic acid), 3‐methoxy‐4‐hydroxyphenolic acids (vanillic and ferulic acids) and their corresponding alkyl esters. Naturally present tocopherols in refined sunflower oil proved to have a synergistic effect on gentisic acid but not on its alkyl esters. In contrast, tocopherols showed an antagonistic effect on alkyl esters of caffeic acid, because their protection factors decreased with increasing level of tocopherols in the test medium. Moreover, the antioxidant activity of these alkyl esters decreased with increasing length of their alkyl chain in conformity with the polar paradox hypothesis. Practical applications: Tocopherols as naturally present antioxidants influence considerably the antioxidant activity of other antioxidants added to plant oils used as a test medium. Distilled fatty acid methyl esters prepared from refined sunflower oil may serve as an optimal tocopherol‐free test medium. Some alkyl esters of phenolic acids were evaluated to be applicable as natural more lipophilic antioxidants in comparison with phenolic acids.     

Gas-liquid chromatographic analysis of cyclopropenoid fatty acids

A method is described for the analysis of cyclopropenoid fatty acids in oils. The method consists of reacting the methyl esters of the cyclopropenoid fatty acids with silver nitrate in methanol to form ether and ketone derivatives. The derivatives formed from the cyclopropenoid fatty acids are separated from the methyl esters of the normal fatty acids by gas-liquid chromatography on a 15% diethylene glycol succinate column. The method is applicable to oils containing from 0.01% to 100% of cyclopropenoid fatty acids. The derivatives of oils containing lew levels of cyclopropenoids are separated from the normal methyl esters by alumina chromatography prior to gas-liquid chromatography. Studies on the quantitative aspects of the derivative formation, alumina chromatography, and gas-liquid chromatography are reported. Analyses for total cyclopropenoid fatty acid content of cottonseed oil andSterculia foetida oil by the gas-liquid chromatographic and hydrobromic acid titration procedures showed good agreement. Replicate analyses of a sample ofSterculia foetida oil for malvalic and sterculic acid gave coefficients of variation of 6.04% and 1.17%, respectively.     

Kinetics of tungsten‐catalyzed sunflower oil epoxidation studied by 1H NMR

Sunflower oil (SO) is a renewable resource that can be epoxidized, and the epoxidized SO has potential uses as an environmentally friendly and reactive material in polymeric formulations, especially for polyvinyl chloride. SO was epoxidized with peracetic acid, which was either preformed or prepared in situ. In order to optimize the formation of oxirane rings, the epoxidation and the extent of the side reactions were studied at different temperatures. The peracetic acid was obtained by acidic catalysis in the presence of a cation‐exchange resin. The optimum conversions were obtained within a 4‐h reaction period at 55 °C by the in situ epoxidation technique. The epoxidation was also carried out with hydrogen peroxide in the presence of peroxotungstic acid complexed with lipophilic phosphorus‐based ligands. ¹H NMR was used to define the new indices Δ and Ω, which are the mean numbers of C=C double bonds and oxirane rings per fatty acid chain, respectively. This allowed monitoring of the reaction and quantification of the results. Peroxotungstic catalysts appeared less performing than peracids in the epoxidation of SO, but were found very efficient for the epoxidation of the SO methyl esters.     

Fatty acids,fatty alcohols,wax esters,and methyl esters fromCrambe abyssinica andLunaria annua seed oils

Crambe abyssinica andLunaria annua, members of the Cruciferae family, have seed oil glycerides containing ca. 55–65% of C₂₂ and C₂₄ unsaturated fatty acids. Fatty acids were prepared by saponification; fatty alcohols, by sodium reduction of glycerides; liquid wax esters, byp-toluenesulfonic acid-catalyzed reaction of fatty acids with fatty alcohols; and methyl esters, by reaction of fatty acids with diazomethane. Solid hydrogenated glyceride oils and wax esters were compared with several commercial waxes. Chemical and physical constants were determined for the seed oils and their derivatives. Position of unsaturation in theCrambe fatty acids was determined by gas chromatographic analysis of the permanganate-periodate degradation products. The major dicarboxylic acid was brassylic (C₁₃), proving the docosenoic acid to be erucic. Presented in part at the AOCS meeting in New Orleans, La., 1962. A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, U.S.D.A.     

The seed oil ofBernardia pulchella (Euphorbiaceae) —A rich source of vernolic acid

The fatty acids from the seed oil ofBernardia pulchella (Euphorbiaceae) have been analyzed by gas chromatography (GC) and GC-mass spectrometry (MS) analysis of their methyl esters. Vernolic acid is the main compound (91%), along with other usual fatty acids. In addition to the quantitation by GC analysis,¹H-nuclear magnetic resonance (NMR) signals from the seed oil have been used to estimate the total epoxy fatty acid content. The structure of vernolic acid has been proven by spectroscopic methods (infrared,¹H, and¹³C-NMR) and by GC-MS analysis of the corresponding silylated hydroxy-methoxy derivative. The 4,4-dimethyloxazoline derivatives of the fatty acid mixture have also been examined by GC-MS, and it was shown that this derivazation reaction is not suitable for the structure analysis of vernolic acid.     

Chemical composition and characteristics ofMoringa peregrina seeds and seeds oil

TheMoringa peregrina kernel contains 1.8% moisture, 54.3% oil, 22.1% protein, 3.6% fiber, 15.3% carbohydrate and 2.5% ash. The composition and characteristics of the extracted oil were determined. Gas liquid chromatography of methyl esters of the fatty acids shows the presence of 14.7% saturated fatty acids and 84.7% unsaturated fatty acids. The fatty acid composition is as follows: palmitic 9.3%, palmitoleic 2.4%, stearic 3.5%, oleic 78.0%, linoleic 0.6%, linolenic 1.6%, arachidic 1.8% and behenic 2.6%.