Relative autoxidative and photolytic stabilities of tocols and tocotrienols

The relative stabilities of selected individual tocols and tocotrienols and of equimolar mixtures of either α- plus γ- or α- plus δ- tocopherols were determined in methyl myristate and methyl linoleate during autoxidation and photolysis. Solutions containing 0.05% of the appropriate tocopherol(s) or tocotrienols were subjected to UV light (254 nm) or to a flow of 4.3 ml/min of oxygen, both at 70 C. Tocopherols (T) and tocotrienols (T−3) were determined by gas chromatography without preliminary separation or purification. Under photolytic conditions, stabilities in increasing order in methyl myristate were γ-T−3<α-T−3<δ-T<α-T <γ-T<5,7-T<β-T and in methyl linoleate were α-T<α-T−3≤γ-T−3≤β-T≤5,7-T <γ-T<δ-T. A solvent effect on the initial rate of photolysis was observed for 5-methyl substituted tocols but not for the tocols with an unsubstituted 5-position or for the tocotrienols. Under autoxidative conditions, stabilities in increasing order in methyl myristate were α-T=α-T−3 <β-T−3<γ-T−3<δ-T−3<γ-T<δ-T=β-T and in methyl linoleate were α-T<α-T−3 <γ-T−3<β-T<γ-T<δ-T. Tocopherols were much more stable during autoxidation in methyl myristate than they were in methyl linoleate. In mixtures, there was no significant protection of α-tocopherol by either γ- or δ-tocopherol under any of the conditions used. However, α-tocopherol was highly effective in protecting γ- and δ-tocopherols in methyl myristate during both photolysis and autoxidation and in methyl linoleate during photolysis. During autoxidation in methyl linoleate, α-tocopherol protection of γ- and δ- tocopherols after 24 hr was slight tough measurable.     

The total synthesis and metabolism of 4-decenoate,dodeca-3,6-dienoate,tetradeca-5,8-dienoate and hexadeca-7,10-dienoate in the fat-deficient rat

Methyl 4-decenoate (10∶1ω6), methyl dodeca-3,6-dienoate (12∶2ω6), methyl tetradeca-5,8-dienoate (14∶2ω6) and methyl hexadeca-7,10-dienoate (16∶2ω6) were prepared by total synthesis. Rats raised on a fat-deficient diet for 2 1/2 months received 100 mg per day of one of the experimental acids or methyl linoleate for a period of 16 days. The liver lipids were extracted, converted to methyl esters and analyzed by gas-liquid chromatography. Neither 10∶1ω6 nor 12∶2ω6 served as biosynthetic precursors for linoleate. Small amounts of 14∶2ω6 were convered to linoleate while 16∶2ω6 served as an efficient precursor for linoleate and longer chain ω6 acids. None of the short chain ω6 acids were incorporated directly into liver lipids.     

Synthesis of substituted fatty oxathiolanes and thioethers from an allylic oxo fatty acid ester

Substituted oxathiolane and thioether derivatives have been synthesized from an allylic oxo fatty acid ester. The reaction of methyl 4-oxo-trans-2-octadecenoate with 3-mercaptopropan-1,2-diol (1-thioglycerol) affords methyl 4-(3′-hydroxymethyl-1′,4′-oxathiolane)-2(3)-(O-mercaptopropan-1″,2″-diol)-octadecanoate (II), methyl 4-oxo-2(3)-(O-mercaptopropan-1′,2′-diol)-octadecanoate (III), methyl 4-(3′-hydroxy-l′,5′-oxathiane)-2 (3)-(S-mercaptopropan-1″,2″-diol)-octadecanoate (IV), methyl 4-oxo-2(3)-(S-mercaptopropan-1′, 2′diol)-octadecanoate (V) and methyl 4-(3′-hydroxymethyl-1′, 4′-oxathiolane)-2(3)-(S-mercaptopropan-1″, 2″-diol)-octadecanoate (VI). Structures of the individual reaction products have been established on the basis of spectral data and microanalyses.     

Free radical addition of hydrogen sulfide to conjugated and nonconjugated methyl esters and to vegetable oils

The rate of addition of hydrogen sulfide to high purity methyl oleate, methyl linoleate, methyl linolenate, methyl 9,11-trans,trans-octade-cadienoate and methyl β-eleostearate was investigated at 25 C with UV irradiation. A similar study was carried out with soybean, linseed and tung oils in the absence and presence of 2,2′-azo-bis(isobutyronitrile) with UV photolysis. Initially the reaction of hydrogen sulfide with methyl esters appears to follow pseudo-zero-order kinetics although as the reaction proceeds the kinetics of the polyunsaturated ester reactions become more complex. For nonconjugated systems the overall rate is determined by the initiation step, whereas the overall rate of addition to conjugated systems is a function of the stability of the resonance-stabilized addition radical in the chain transfer step. For methyl esters the following order of reactivity appears to hold: Methyl oleate ≅ methyl linoleate ≅ methyl linolenate >> methyl 9,11-trans,trans-octadecadienoate > methyl β-eleostearate. Using 2,2′-azo-bis(isobutyronitrile) with UV photolysis markedly increases the rate of addition of hydrogen sulfide to nonconjugated vegetable oils. Presented at the AOCS Meeting, New York, October 1968. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Synthesis of sulfur-Containing derivatives from olefinic fatty esters

The reaction of 3-mercaptopropan-l,2-diol with methyl 10-undecenoate (Ib) yielded three products, methyl 11-(3′-mercaptopropan-l′,2′-diacetoxy) undecanoate (II, 48.9%), methyl 11-(1-oxapropan-2′-acetoxy-3′-mercaptoacetyl) undecanoate (III, 27.4%) and methyl 10-(3′-mercaptopropan-1′-acetoxy-2′-ol) undecanoate (IV, 23.0%) along with hydrolyzed starting material (Ia, 5.4%). The same reaction with methyl 9-octadecenoate (Vb) gave an isomeric product, 9(10)-(3′-mercaptopropan-l′-acetoxy-2′-ol) octadecanoic acid (VI, 78.5%) and oleic acid (Va, 21.4%). Reaction withtrans-2-octadecenoic acid (VII) afforded 2(3)-(3′-mercaptopropan-l′-acetoxy-2′-ol) octadecanoic acid (VIII, 85.7%).     

Carotenoids from red palm methyl esters by nanofiltration

Palm oil contains high concentrations of carotenoids and tocopherols that can be recovered by first converting them to methyl esters and then applying membrane technology to separate the carotenoids from the methyl esters. Several solvent-stable nanofiltration membranes were investigated for this application. Flux with a model red palm methyl ester solution ranged from 0.5 to 10 Lm⁻²h⁻¹, and rejection of β-carotene was 60–80% at a transmembrane pressure of 2.76 MPa and 40°C. A multistage membrane process was designed for continuous production of palm carotene concentrate and decolorized methyl esters. With a feed rate of 10 tons per hour of red palm methyl esters containing 0.5 gL⁻¹ β-carotene, the process could produce 3611 L·h⁻¹ of carotene concentrate containing 1.19 gL⁻¹ carotene and 7500 Lh⁻¹ of decolorized methyl esters containing less than 0.1 gL⁻¹ β-carotene. The economics of this process is promising.     

Separation of bile acid methyl esters by high-performance liquid chromatography

Conjugated bile acids, namely glyco- and tauro-3α,6α-dihydroxy-5β-cholanoic acid (hyodeoxycholic acid), 3α,7α-dihydroxy-5β-cholanoic acid (chenodeoxycholic acid), 3α,6α,7α-trihydroxy-5β-cholanoic acid (hyocholic acid) and 3α-hydroxy-6-oxo-5β-cholanoic acid (6-keto-litocholic acid) were isolated from pig bile, and subsequently transformed into the corresponding methyl esters. Separation of the methyl esters of the isolated bile acids by high-performance liquid chromatography (HPLC) was accomplished on a ZORBAX-CN column (Dupont, Boston, MA) withn-hexane/2-propanol/methylene chloride (89∶6∶5, by vol) as the mobile phase containing traces (≈1%) of amyl alcohol and water as moderators. HPLC analysis of the methyl esters also showed the presence of methyl 3α-hydroxy-6-oxo-5α-cholanoate, which was probably produced in the course of alkaline hydrolysis of the conjugated bile acids.     

Reaction of α-tocopherol in heated bulk phase in the presence of methyl linoleate (13S)-hydroperoxide or methyl linoleate

α-Tocopherol and methyl (9Z, 11E)-(S)-13-hydroperoxy-9, 11-octadecadienoate (13-MeLOOH) were allowed to stand at 100°C in bulk phase. The products were isolated and identified as methyl 13-hydroxyoctadecadienoate (1), stereoisomers of methyl 9,11,13-octadecatrienoate (2), methyl 13-oxo-9, 11-octadecadienoate (3), epoxy dimers of methyl linoleate with an ether bond (4), a mixture of methyl (E)-12, 13-epoxy-9-(α-tocopheroxy)-10-octadecenoates and methyl (E)-12, 13-epoxy-9-(α-tocopheroxy)-11-(α-tocopheroxy)-9-octadecenoates (5), a mixture of methyl 9-(α-tocopheroxy)-10,12-octadecadienoates and methyl 13-(α-tocopheroxy)-9, 11-octadecadienoates (6), α-tocopherol spirodiene dimer (7), and α-tocopherol trimer (8). α-Tocopherol and 13-MeLOOH were dissolved in methyl myristate, and the thermal decomposition rate and the distributions of reaction products formed from α-tocopherol and 13-MeLOOH were analyzed. α-Tocopherol disappeared during the first 20 min, and the main products of α-tocopherol were 5 and 6 with the accumulation of 1–4 which were the products of 13-MeLOOH. The results indicate that the alkyl and alkoxyl radicals from the thermal decomposition of 13-MeLOOH could be trapped by α-tocopherol to produce 5 and 6. The reaction products of α-tocopherol during the thermal oxidation of methyl linoleate were compounds 6 and 7. Since the radical flux during the autoxidation might be low, the excess α-tocopheroxyl radical reacted with each other to form 7.     

Oxidation of methyl formylstearate with molecular oxygen

Methyl formylstearate, containing soluble rhodium complex from rhodium-catalyzed hydroformylation of methyl oleate, is oxidized in an emulsion to methyl carboxystearate. The reaction is carried out in a closed system at 20–25 C in the presence of either air or oxygen (1–3 atm). Conversion to methyl carboxystearate is 87–89% in 2–3 hr; when catalytic amounts of calcium acetate are present, 93–95% is converted. The principal byproduct of oxidation is methyl formyloxystearate, formation of which is suppressed by calcium acetate. Distillation of crude methyl carboxystearate yields a residue containing soluble rhodium (and calcium acetate if used), which after calcining in the presence of a refractory support produces an effective hydroformylation catalyst. Recovery and regeneration of this catalyst provide an economically feasible batch process for methyl carboxystearate. Presented at AOCS spring meeting, Dallas, April, 1975.     

The Influence of Tocopherols on the Oxidation Stability of Methyl Esters

Tocopherols were found to be the principal natural antioxidants in biodiesel grade fatty acid methyl esters. The stabilising effect of α-, γ- and δ- tocopherols from 250 to 2,000 mg/kg was evaluated by thermal and accelerated storage induction times based on rapid viscosity increase, in sunflower (SME), recycled vegetable oil (RVOME), rapeseed (RME) and tallow (TME) methyl esters. Both induction times showed that stabilising effect is of the order of δ- > γ- > α-tocopherol, and that the stabilising effect increased with concentration. The correlation between the two induction times however was poor, which is probably due to the fact that the time they correspond to two different stages of oxidation. Tocopherols were found to stabilise methyl esters by reducing the rate of peroxide formation while present. The deactivation rates of tocopherols increased with unsaturation of the particular methyl ester and in the present work they were of the order of SME > RME > RVOME > TME. While α-tocopherol was found to be a relatively weak antioxidants, both γ- and δ- tocopherols increased induction times significantly and should be added to methyl esters without natural antioxidants.     

Analysis of the dark-colored impurities in sulfonated fatty acid methyl ester

A fractionally distilled C₁₄−C₁₆ fatty acid methyl ester, derived from palm oil, was sulfonated with gaseous SO₃ in a falling film reactor to form an α-sulfo fatty acid methyl ester (α-SF; unbleached and unneutralized form). The included dark-colored impurities were then separated from α-SF as a diethyl ether-insoluble matter. After purification by thin-layer chromatography, the colored species were analyzed by ion-exchange chromatography, gel-permeation chromatography, and nuclear magnetic resonance spectrometry. These data suggested that the colored species were polysulfonated compounds with conjugated double bonds. Minor components in the raw fatty acid methyl ester, found by gas chromatography/mass spectrometry, were spiked into the purified methyl palmitate and then sulfonated. The unsaturated methyl ester and hydroxy ester showed the worst color results. The methyl oleate and methyl 12-hydroxystearate were then sulfonated and analyzed. Deep black products were obtained, which showed the same properties as the colored species in α-SF. It was concluded that low levels of unsaturated fatty acid methyl esters and hydroxy esters in the fatty acid methyl ester are the main causes of the coloring.     

Dilatometric investigations of fatty acid methyl esters

Summary The coefficients of expansion and melting dilations were measured for methyl palmitate, methyl stearate, methyl arachidate, methyl behenate, and methyl oleate. The dilatometric curve for the heating cycle of methyl palmitate and methyl stearate in the solid state was composed of a linear section to 49 degrees below the melting point, followed by a curvilinear section to the melting point. The heating and cooling cycle curves for methyl palmitate show the same volume change from −38°C. to 29°C., but the shape of the curves is different. The same relation holds for methyl stearate from −38°C. to 37.5°C. “After-contractions” were found in volume measurements within a few degrees of the melting point of both esters. Equilibrated points were found within 0.5 degrees of the final melting temperature of methyl stearate. A striking similarity exists between curves for variation of the dielectric constant with temperature for long chain linear molecules and the dilatometric data. Presented at the fall meeting, American Oil Chemists' Society, Mnneapolis, Minn., October 11, 1954. Issued as Paper No. 196 on the “Uses of Plant Products” and as N.R.C. No. 3671.     

Prooxidant effects of inorganic chromium compounds in the autoxidation of methyl linoleate

The prooxidant property of inorganic chromium compounds was determined in methyl linoleate free from natural antioxidants and metals. Prooxidant properties of inorganic chromium compounds appeared in order of sodium chromate > chromium (VI)-oxide > chromium chloride > potassium chromate > chromium (III)-oxide > potassium dichomate. In comparison with the control, additions of chromium compounds induced different amounts of autoxidation products derived from methyl linoleate, such as small amounts of hydroperoxides and conjugated dienes and large amounts of hydroxy groups,α,β,γ,δ-unsaturated carbonyls, isolatedtrans double bonds, polymers, and free radicals. From these analytical data, the catalysis of chromium compounds in the autoxidation of methyl linoleate seemed to be based on their abilities of abstracting a hydrogen from methyl linoleate and decomposing hydroperoxides derived from the autoxidation of methyl linoleate.     

The behavior of sterols on silica surfaces and at other interfaces

The specific manner in which a molecule is oriented at an interface determines the reactions in which the molecule can participate. Sterols, being highly anisotropic molecules, present “ends” and “sides” to surfaces which differ greatly in their reactivity and interaction with the surface. Seen from the 3β-hydroxy end, as at an air-water interface, sterols are largely indistinguishable from one another in their behavior. On the other hand, at an organized interface, such as that of an absorbent, a great many differences in structure can be demonstrated. These include the distinction between nuclear and side-chain double bonds, the number and location of nuclear double bonds, the substituents in the side chain and the number of methyl groups in the molecule. We have been interested in the degree of specificity which such interaction can display because of the obvious parallel to sterol-protein interactions of a structural or enzymatic nature. Through the synthesis of a variety of sterol structures possessing the desired arrangement of double bonds and numbers of methyl groups, we have established a reproducible correlation between adsorptive interaction and double bonds in the Δ⁵, Δ⁷, Δ⁸, Δ^5,7 and Δ^{7, 9} positions, as well as for the saturated stanol. These correlations have been extended for the 4α, 4β, 4,4 dimethyl and 4,4,14α trimethyl series as well. The elucidation of the structure of macdougallin as a 14α methyl sterol in which the 4,4, gem dimethyl grouping was absent prompted a further study of the 14α methyl sterols, of which the Δ⁷, Δ⁸, Δ^7,9 and unsaturated varieties have been prepared and tested. The presence of a 14α methyl group in the absence of other methyl groups confers a unique behavior on the molecule in that this series does not fit into the adsorptive scheme for the other sterols. Instead, the interaction of the double bond with the surface is almost completely independent of its position, suggesting that the molecule is “perched” on the 14α methyl group when absorbed in the surface. This appears to be a highly significant feature in the orientation of the molecule, since the removal of this methyl group is usually regarded as an essential first step in the conversion of lanosterol to cholesterol.     

Estimation of heat of combustion of triglycerides and fatty acid methyl esters

Equations were developed for the estimation of gross heat of combustion (HG) of triglycerides (TGs) and fatty acid methyl esters (FAMEs) from their saponification number (SN) and iodine value (IV). HG of TG=1,896,000/SN − 0.6 IV — 1600 and HG of FAME=618,000/SN − 0.08 IV — 430. When these equations were tested on cottonseed oil, soybean oil, partially hydrogenated soybean oil, peanut oil, sunflower oil, sunflower oil methyl esters, soybean oil methyl esters and cottonseed oil methyl esters, predicted HG values agreed well with those reported in the literature.     

Composition of methyl esters from heat-bodied linseed oils

Two heat-bodied linseed oils, with Gardner viscosities of 37 and 55 min, were saponified, converted to their methyl esters, and separated into 2 fractions with urea and methanol. Gas-liquid chromatography showed the adduct fraction, which comprised 38–41% of the total methyl esters, to contain: palmitic, stearic, oleic, “linoleic,” and trace amounts of “linolenic” acid. The nonadducting fraction (59–62%) of the total methyl esters was separated by molecular distillation at 140C/7 μ into a distillate and residue. The distillate amounted to 18–25% of the total methyl esters and had an iodine value (I.V.) of 142–145; its absorption at 232 mμ indicates 2.5–3.0% conjugated diene. Hydrogenation of this distillate gave a liquid product with an iodine number of 4 and a pour point of −50C. Gas chromatograms of the distillate and its hydrogenated derivative indicated at least 5–7 components. Comparison of these peaks with known fatty acid methyl esters indicates that the components of these fractions were either cyclic or branched esters. The nonadducting residue fraction was composed mainly of polymeric acids. Presented before the Division of Organic Coatings and Plastics Chemistry, Am. Chem. Soc. Washington, D.C., 1962. A laboratory of the No. Utiliz. Res. & Dev. Div., ARS, U.S.D.A.     

Reaction of α-tocopherol with alkyl and alkylperoxyl radicals of methyl linoleate

α-Tocopherol was reacted with alkyl and alkylperoxyl radicals at 37°C in bulk phase. The lipid-free radicals were generated by the reaction of methyl linoleate with the free radical initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (AMVN) under air-insufficient conditions. The products were isolated by high-performance liquid chromatography. Their structures were identified as 2-(α-tocopheroxy)-2,4-dimethylvaleronitrile (1), a mixture of methyl 9-(8a-peroxy-α-tocopherone)-10(E),12(Z)-octadecadienoate and methyl 13-(8a-peroxy-α-tocopherone)-9(Z),11(E)-octadecadienoate (2), methyl 9-(α-tocopheroxy)-10(E),12(Z)-octadecadienoate (3a), methyl 13-(α-tocopheroxy)-9(Z),11(E)-octadecadienoate (3b), α-tocopherol spirodiene dimer (4) and α-tocopherol trimer (5). When methyl linoleate containing α-tocopherol was oxidized with AMVN under airsufficient conditions, the main products were 8a-alkyl-peroxy-α-tocopherones (2). In addition to these compounds, 6-O-alkyl-α-tocopherols (1, 3a and 3b) were formed when the reaction was carried out under air-insufficient conditions. The results indicate that α-tocopherol can react with both alkyl and alkylperoxyl radicals during the autoxidation of polyunsaturated lipids.     

Preparation of heptadecenoic acid fromCandida tropicallis yeast

In this paper a method is described for preparing 10 g or more of heptadecenoic acid (C17:1ω8) of 99 p.100 purity fromCandida tripicallis yeast. Three cycles of treatment, based on crystallization techniques, were used successively: (1) Crystallization of fatty acids (in free form) from acetone at −25 C induced the elimination of most of the saturated fatty acids, and at −60 C, of all of the poly-unsaturated acids. (2) Inclusion formation of fatty acids (as methyl esters) with urea at hC induced the removal of all of the remaining saturated methyl esters and most of methyl oleate. (3) Crystallization of fatty acid methyl esters from acetone at −60 C removed almost all the remaining monounsaturated methyl esters (methyl palmitoleate and methyl oleate). Total efficiency of the preparation was about 17 p. 100.     

Iron-catalyzed reaction products of α-tocopherol with methyl 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoate

α-Tocopherol was reacted with methyl 13(S)-hydroperoxy-9(Z),11(E)-octadecadienoate in the presence of an iron-chelate, Fe(III)-acetylacetonate, at 37°C in benzene. The reaction was carried out either aerobically or anaerobically. The main products of α-tocopherol under air were isolated and identified as two stereoisomers of 4a,5-epoxy-8a-hydroperoxy-α-tocopherone, four stereoisomers of methyl 9-(8a-dioxy-α-tocopherone)-12,13-epoxy-10(E)-octadecenoate, four stereoisomers of methyl 11-(8a-dioxy-α-tocopherone)-12,13-epoxy-9(Z)-octadecenoate, two stereoisomers of methyl 13(S)-(8a-dioxy-α-tocopherone)-9(Z),11(E)-octadecadinoate, and α-tocopherol dimer. Besides the 8a-(lipid-peroxy)-α-tocopherones, two stereoisomers of methyl 11-(α-tocopheroxy)-12(S),13(S)-epoxy-9(E)-octadecenoate, two stereoisomers of methyl 9-(α-tocopheroxy)-12(S),13(S)-epoxy-10(E)-octadecenoate, and two isomers of methyl (α-tocopheroxy)-octadecadienoate were obtained under nitrogen atmosphere. The results indicate that the peroxyl radicals from lipid hydroperoxides prefer to react with the 8a-carbon radical of α-tocopherol and the carbon-centered radicals react with the phenoxyl radical of α-tocopherol.     

Radical Scavenging Activity and Performance of Novel Phenolic Antioxidants in Oils During Storage and Frying

Novel phenolic antioxidants: 2a (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-yl)methyl 3-methoxy-4-hydroxycinnamate, 2b (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-yl)methyl 3,5-dimethoxy-4-hydroxycinnamate, 2c (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-yl)methyl 3,4-dihydroxycinnamate, and 3 (6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)methyl (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-carboxylate) have been prepared in good yields and fully characterized by ¹H and ¹³C NMR, and HRMS. Their radical scavenging activities have been evaluated by DPPH and ORAC assays. Each of the synthesized antioxidants exhibited significantly higher radical scavenging activities than trolox and α-tocopherol. These novel antioxidants efficiently protected canola oil triacylglycerides (CTG) during accelerated storage and frying. Compounds 2c and 3 were significantly more efficient than α-tocopherol protecting CTG under accelerated storage. All new antioxidants were more efficient than α-tocopherol under frying conditions and present significantly higher thermal stability.