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.     

Isomerization during hydrogenation of soap: II. Potassium elaidate and potassium linoleate

Potassium elaidate in slightly alkaline solution was hydrogenated for up to 7 hr with 1.5% of Rufert nickel catalyst at 150 C and 20 kg/sq cm pressure. Potassium linoleate was similarly hydrogenated with 1.0% catalyst for 7 hr, and the hydrogenation continued for another 7 hr after addition of 0.5% fresh catalyst. Periodic samples from each were analyzed for component acids. The positional isomers in thecis andtrans monoenes, isolated by preparative argentation thin layer (TLC) or column chromatography, were estimated after oxidation to dicarboxylic acids. Some diene fractions were isolated for further examination. In potassium elaidate hydrogenation,cis monoenes were initially produced in considerable amounts, but to a lesser extent thereafter. Positional isomers were similarly distributed in bothcis andtrans monoenes after prolonged hydrogenation. In the hydrogenation of potassium linoleate, a drop in iodine value (IV) of 60 units occurred in the first hour, and 38% oftrans monoenes (in which the 10- and 11-monoenes constitute 32% each) were formed. The IV then fell only slowly, and up to 38% ofcis monoene (mostly 9- and 12-isomers) was formed. Addition of fresh catalyst caused a major shift ofcis monoenes totrans forms. The diene fraction was mostly nonconjugated material with the first double bond at the 9, 8 and 10-positions. Minor amounts of conjugated dienes were present as well as a dimeric product.     

Catalytic hydrogenation of linoleic acid on nickel,copper, and palladium

The catalytic activity and selectivity for hydrogenation of linoleic acid were studied on Ni, Cu, and Pd catalysts. A detailed analysis of the reaction product was performed by a gas-liquid chromatograph, equipped with a capillary column, and Fourier transform-infrared spectroscopy. Geometrical and positional isomerization of linoleic acid occurred during hydrogenation, and many kinds of linoleic acid isomers (trans-9,trans-12; trans-8,cis-12 orcis-9,trans-13; cis-9,trans-12; trans-9,cis-12 andcis-9,cis-12 18∶2) were contained in the reaction products. The monoenoic acids in the partial hydrogenation products contained eight kinds of isomers and showed different isomer distributions on Ni, Cu, and Pd catalysts, respectively. The positional isomers of monoenoic acid were produced by double-bond migration during hydrogenation. On Ni and Pd catalysts, the yield ofcis-12 andtrans-12 monoenoic acids was larger than that ofcis-9 andtrans-9 monoenoic acids. On the contrary, the yield ofcis-9 andtrans-9 monoenoic acids was larger than that ofcis-12 andtrans-12 monoenoic acids on Cu catalyst. From these results, it is concluded that the double bond closer to the methyl group (Δ12) and that to the carboxyl group (Δ9) show different reactivity for hydrogenation on Ni, Cu, and Pd catalysts. Monoenoic acid formation was more selective on Cu catalyst than on Ni and Pd catalysts.     

Formation and distribution of oxidized fatty acids during deep‐ and pan‐frying of potatoes

The formation of cis‐9,10‐epoxystearate, trans‐9,10‐epoxystearate, cis‐9,10‐epoxyoleate, cis‐12,13‐epoxyoleate, trans‐9,10‐epoxyoleate, trans‐12,13‐epoxyoleate and the co‐eluting 9‐ and 10‐ketostearates during eight successive pan‐ and deep‐frying sessions of pre‐fried potatoes in five different types of vegetable oils – namely cottonseed oil, sunflower oil, vegetable shortening, palm oil and virgin olive oil – was followed and quantified both in fried oils and in fried potatoes by GC/MS after derivatization to methyl esters. These oxidized fatty acids were present at relatively low concentrations in the fresh oils and pre‐fried potatoes while they increased linearly with frying time, reaching up to 1140.8 µg/g in virgin olive oil (VOO) and 186.9 µg/g in potatoes pan‐fried in VOO after eight pan‐frying sessions, with trans‐9,10‐epoxystearate predominating in all cases. The formation of polymerized triacylglycerols (PTG) was also quantified in frying oils by size exclusion HPLC. Pan‐frying caused higher oxidized fatty acid and PTG formation compared to deep‐frying. Epoxyoleates and PTG concentrations were increased after frying in polyunsaturated oils, while epoxystearate and 9‐ and 10‐ketostearate concentrations were increased after frying in monounsaturated oils. No specific absorption of the oxidized fatty acids by the fried potatoes seems to occur. The dietary intake of oxidized fatty acids and PTG by the consumption of fried potatoes was discussed.     

Production of Low-trans Fatty Acids Edible Oil by Electrochemical Hydrogenation in a Diaphragm Reactor Under Controlled Conditions

Electrochemical hydrogenation is a novel, alternative process for selective hydrogenation of vegetable oils, because of its high extent of hydrogenation and low trans-isomer formation. Electrochemical hydrogenation of soybean oil in a diaphragm reactor with a formate ion concentration of 0.4 mol/l at pH 5.0 under moderate temperature conditions using a current density of 10 mA/cm² was investigated to identify the critical conditions affecting the selective hydrogenation reaction and the resulting fatty acid profile. The optimum composition was an oil-to-formate solution ratio of 0.3 (w/w), 2?C3 g EDDAB in 100 g soybean oil, and 0.8% Pd?CC catalyst loading. The electrochemical hydrogenation reaction of soybean oil was described by first-order kinetics, and the kinetic rate constants and reaction selectivity were determined accordingly. Re-use of the Pd?CC catalyst up to five times was found to be acceptable. A comprehensive evaluation revealed that the most significant conditions affecting the extent of hydrogenation and the trans fatty acids content of final products were operating temperature, pH of the formate solution, and catalyst loading.     

Selective homogeneous hydrogenation of triunsaturated fats catalyzed by tricarbonyl chromium complexes

The need for a selective catalyst to hydrogenate linolenate in soybean oil has prompted our continuing study of various model triunsaturated fats. Hydrogenation of methylβ-eleostearate (methyltrans,trans,trans-9,11,13-octadecatrienoate) with Cr(CO)₃ complexes yielded diene products expected from 1,4-addition (trans-9,cis-12- andcis-10,trans-13-octadecadienoates). Withα-eleostearate (cis,trans,trans-9,11,13-octadecatrienoate), stereoselective 1,4-reduction of thetrans,trans-diene portion yielded linoleate (cis,cis-9,12-octadecadienoate). However,cis,trans-1,4-dienes were also formed from the apparent isomerization ofα- toβ-eleostearate. Hydrogenation of methyl linolenate (methylcis,cis,cis-9,12,15-octadecatrienoate) produced a mixture of isomeric dienes and monoenes attributed to conjugation occurring as an intermediate step. The hydrogenation ofα-eleostearin in tung oil was more stereoselective in forming thecis,cis-diene than the corresponding methyl ester. Hydrogenation of linseed oil yielded a mixture of dienes and monoenes containing 7%trans unsaturation. We have suggested how the mechanism of stereoselective hydrogenation with Cr(CO)₃ catalysts can be applied to the problem of selective hydrogenation of linolenate in soybean oil. No. Market. Nutr. Res. Div., ARS, USDA.     

Fatty acid and conjugated linoleic acid isomer profiles in human milk fat

The fatty acid composition of 39 mature human milk samples from four Spanish women collected between 2 and 18 weeks during lactation was studied by gas chromatography. The conjugated linoleic acid (CLA) isomer profile was also determined by silver‐ion HPLC (Ag⁺‐HPLC) with three columns in series. The major fatty acid fraction in milk lipids throughout lactation was represented by the monounsaturated fatty acids, with oleic acid being the predominant compound (36–49% of total fatty acids). The saturated fatty acid fraction represented more than 35% of the total fatty acids, and polyunsaturated fatty acids ranged on average between 10 and 13%. Mean values of total CLA varied from 0.12 to 0.15% of total fatty acids. The complex mixture of CLA isomers was separated by Ag⁺‐HPLC. Rumenic acid (RA, cis‐9 trans‐11 C18:2) was the major isomer, representing more than 60% of total CLA. Trans‐9 trans‐11 and 7‐9 (cis‐trans + trans‐cis) C18:2 were the main CLA isomers after RA. Very small amounts of 8‐10 and 10‐12 C18:2 (cis‐trans + trans‐cis) isomers were detected, as were different proportions of cis‐11 trans‐13 and trans‐11 cis‐13 C18:2. Although most of the isomers were present in all samples, their concentrations varied considerably.     

Hydrogenation of dienes with cationic rhodium complexes

Methylcis-9,cis-12-octadecadienoate (methyl linoleate;c9,c12), itst10,t12 andt10,c12 isomers and methylcis-9-octadecenoate (methyl oleate;c9) were hydrogenated with rhodium complexes, the active species of which consisted of [RhL₂]⁺ and [RhL₂H₂]⁺ with ligands L=P(C₂H₅)₂C₆H₅ (catalyst A) P(i-C₄H₉)₃ (catalyst B) and P(CH₃)₃ (catalyst C). Using these catalysts the influence of steric effects on the reaction mechanism of hydrogenation of dienes was studied. The reactions were carried out in 2-propanol at atmospheric hydrogen pressure and ambient temperature. During hydrogenation ofc9 on catalysts A and B, geometrical isomerization mainly occurred, whereas on catalyst C some positional isomerization also took place.C9,c12 was almost exclusively hydrogenated via conjugated intermediates on catalyst A. On catalyst C, one of the double bonds was hydrogenated directly, in most cases. In the absence of hydrogen, catalysts A and B conjugatedc9,c12 very fast. The conjugation activity of catalyst C was much lower. Catalyst C showed a high 1,5-shift activity for the conjugatedcis, trans andtrans, cis intermediates during hydrogenation, in contrast to catalysts A and B, which showed a poor activity in this respect.T10,t12 was hydrogenated almost exclusively via 1,4-addition of hydrogen to thecisoid conformation, whereas only a slight preference was found in this mechanism over 1,2-addition for the hydrogenation oft10,c12. On the sterically unhindered catalysts A and C thetrans double bond int10,c12 was preferentially hydrogenated whereas on catalyst B, with its bulky ligands, thecis double bond was reduced faster than thetrans double bond.     

Hydrogenation of alkali-conjugated linoleate: Isomeric monoene profiles obtained with nickel,palladium and platinum catalysts

Alkali-conjugated linoleate (cis-9,trans-11- andtrans-10,cis-12-octadecadienoate) was hydrogenated with nickel, palladium and platinum catalysts. Thetrans andcis monoenes formed during reduction were isolated, and their double bond distribution was determined by reductive ozonolysis and gas liquid chromatography. About 44–69% of the monoenes were composed of δ¹⁰ and δ¹¹ trans monoene isomers, whereas the δ⁹ and δ¹² cis monoenes amounted to 20–26%. With nickel catalyst, composition of monoene isomers remained the same, even when the hydrogenation temperature was increased. The monoene isomer profiles between nickel and palladium catalysts were indistinguishable. Isomerization of monoenes with platinum catalyst was suppressed at 80 psi. The position of the double bonds in unreacted conjugated diene was always retained, except with nickel at both temperatures and with platinum at 150 C when a slight migration occurred. Geometrical isomerization totrans,trans-conjugated diene was observed in the unreacted diene with nickel (ca. 15% of diene) at both 100 C and 195 C, and with platinum (ca. 7% of diene) at 150 C. ARS, USDA.     

Hydrogenation of a menhaden oil: I. Fatty acid and C20 monoethylenic isomer compositions as a function of the degree of hydrogenation

US menhaden oil is rich in long-chain polyethylenic fatty acids, chiefly C₂₀ (eicosapentaenoic) and C₂₂ (docosahexaenoic) fatty acids, unlike Canadian herring oil, which is rich in long-chain (C₂₀ and C₂₂) monoethylenic fatty acids. An examination of the product fatty acids from hydrogenation of menhaden oil therefore comple-ments studies previously published for herring oil. During a commer-cial hydrogenation of menhaden oil, iodine value (IV) 159.0, on nickel catalyst, samples were collected at IV 150.0, 140.0, 131.5, 120.5, 96.5, 90.0 and 84.5. The fatty acid compositions were deter-mined using a combination of mercuric adduct fractionation and gas liquid chromatographic (GLC) analyses, and the totaltrans content by infrared spectroscopy. The partial hydrogenation resulted in the disappearance of the pentaenoic and hexaenoic fatty acids, a de-crease in tetraenes, and a definite increase in trienes, 8.3% at IV 84.5 compared to 4.2% at IV 159.0. The dienoic fatty acids in-creased to 13.2% at IV 84.5 compared to 4.1% at IV 159.0, and the monoenoic fatty acids increased to 34.2% from 24.0%. No impor-tant changes in the saturated acids were observed, 43.8% at IV 84.5 compared to 41.6% at IV 159.0. The totaltrans content varied from 3.4% at IV 150.0 to 45.1% at an IV of 84.5. The isomer composi-tions of thecis andtrans C₂₀ monoethylenic fatty acids were deter-mined using a combination of preparative GLC, AgNO₃ thin layer chromatography and ozonolysis. Thecis 20:1 acids at IV 84.5 still retained 27.5% of the major isomer (All) originally present at 72%. The parent A5, A8, All, A14 and A17 bonds of the 20:5 originally present could be detected in thecis 20:1 isomers at IV 96.5 but not at IV 84.5. At IV 84.5, 58% of the 20:1was trans, the major isomer being All (9.4% of total 20.1), accompanied by important quanti-ties of Δ10 and Δ12, respectively, 6.9% and 6.6% of the total 20:1. Presented in part at the 73rd annual AOCS meeting, Toronto, 1982.     

High Oleic and Low <Emphasis Type="Italic">Trans</Emphasis> Fatty Acid Formation by an Electrochemical Process

Electrochemical hydrogenation employing a mediator of formate/formic acid resulted in partial hydrogenation of vegetable and soybean oil at 20–40 °C and ambient pressure when palladium supported on alumina was employed as a catalyst. An oleic acid content of 48% with a corresponding iodine value of 81 for the vegetable oil hydrogenated at 20 °C was obtained. The total trans fatty acid content and especially the 18:1 trans fatty acid were found to increase with the reaction temperature and time. Nonetheless, relatively low total trans and 18:1 trans fatty acid (7 and 3.8%, respectively) contents were found when the vegetable oil was partially hydrogenated to achieve an iodine value of 112.     

Synthesis of methyl 9,12-epoxyoctadecanoate from castor oil

We report here the synthesis of methyl 9,12-epoxyoctadecanoate (2-[7-methoxycarbonyl-heptyl]-5-hexanyl-tetrahydrofuran). Methyl ricinoleate (methyl 12-hydroxy-9-cis-octadecenoate), isolated from castor oil methyl esters was isomerized with diphenyl disulfide as radical initiator under ultraviolet radiation to give thetrans isomer, methyl ricinelaidate. The latter was cyclized by slow addition of 10% bromine solution in dichloromethane to give methyl 10-bromo-9,12-epoxyoctadecanoate, which on hydrogenation with Pd/C catalyst gave the title compound, methyl 9,12-epoxyoctadecanoate.     

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.     

Hydrogenation of fatty oils with palladium catalysts. V. Products of the tall oil industry

Conditions were found for reducing tall oil distillate to an iodine number of 22 with a sufficiently small amount of palladium catalyst to make the process commereially feasible. The operating conditions were 200°C and 2,600 psi. Tall oil fatty acids were reduced with palladium and the concentration of linoleic acid,cis-oleic acid, saturated acid, andtrans isomers were determined as a function of iodine number. The five-platinum group metals (Pt, Pd, Ir, Rh, Ru) were compared as to activity, selectivity of partial hydrogenation, and tendeney to formtrans-isomers.     

Direct Isomerization of Linoleic Acid to Conjugated Linoleic Acids (CLA) using Gold Catalysts

Supported gold catalysts, e.g., Au on Al₂O₃, Fe₂O₃, CeO₂, MnO₂, TiO₂, ZrO₂, activated carbon, titanium silicalite TS‐1, were prepared and used for the isomerization of linoleic acid (cis‐9,cis‐12‐octadecadienoic acid) to conjugated linoleic acids (CLA) in the presence of hydrogen at 165 °C in a batch reactor. The best results were obtained using a catalyst with 2 wt % Au on TS‐1, which exhibits a high selectivity (78 %) towards CLA. The two biologically active target CLA isomers, i.e., cis‐9,trans‐11‐CLA and trans‐10,cis‐12‐CLA, were the main products. During the isomerization of linoleic acid to CLA, consecutive reactions also took place. These were the hydrogenation of linoleic acid and CLA to monounsaturated octadecenoic acids and the further hydrogenation of monounsaturated acids to stearic acid. Thus, gold catalysts are capable of isomerizing linoleic acid to CLA and hydrogenating their double bonds to an extent that depends on the Au catalyst used.     

Homolytic decomposition of linoleic acid hydroperoxide: Identification of fatty acid products

An isomeric mixture of linoleic acid hydroperoxides, 13-hydroperoxy-cis-9,trans-11-octadecadienoic acid (79%) and 9-hydroperoxy-cis-12,trans-10-octadecadienoic acid (21%), was decomposed homolytically by Fe(II) in an ethanol-water solution. In one series of experiments, the hydroperoxides were decomposed by catalytic concentrations of Fe(II). The 10⁻⁵ M Fe(III) used to initiate the decomposition was kept reduced as Fe(II) by a high concentration of cysteine added to the reaction in molar excess of the hydroperoxides. Nine different monomeric (no detectable dimeric) fatty acids were identified from the reaction. Analyses of these fatty acids revealed that they were mixtures of positional isomers identified as follows: (I) 13-oxo-trans,trans-(andcis,trans-) 9,11-octadecadienoic and 9-oxo-trans,trans- (andcis,trans-) 10,12-octadecadienoic acids; (II) 13-oxo-trans-9,10-epoxy-trans-11-octadecenoic and 9-oxo-trans-12, 13-epoxy-trans-10-octadecenoic acids; (III) 13-oxo-cis-9,10-epoxy-trans-11-octadecenoic and 9-oxo-cis-12, 13-epoxy-trans-10-octadecenoic acids; (IV) 13-hydroxy-9,11-octadecadienoic and 9-hydroxy-10,12-octadecadienoic acids; (V) 11-hydroxy-trans-12, 13-epoxy-cis-9-octadecenoic and 11-hydroxy-trans-9, 10-epoxy-cis-12-octadecenoic acids; (VI) 11-hydroxy-trans-12, 13-epoxy-trans-9-octadecenoic and 11-hydroxy-trans-9,10-epoxy-trans-12-octadecenoic acids; (VII) 13-oxo-9-hydroxy-trans-10-octadecenoic acids; (VIII) isomeric mixtures of 9, 12, 13-dihydroxyethoxy-trans-10-octadecenoic and 9, 10, 13-dihydroxyethoxy-trans-11-octadecenoic acids; and (IX) 9, 12, 13-trihydroxy-trans-10-octadecenoic and 9, 10, 13-trihydroxy-trans-11-octadecenoic acids. In another experiment, equimolar amounts of Fe(II) and hydroperoxide were reacted in the absence of cysteine. A large proportion of dimeric fatty acids and a smaller amount of monomeric fatty acids resulted. The monomeric fatty acids were examined by gas liquid chromatography-mass spectroscopy. Spectra indicated that the monomers were largely similar to those produced by the Fe(III)-cysteine reaction. Presented in part at the American Chemical Society Meeting, Los Angeles, March 1974. ARS, USDA.     

Quantitative determination of conjugated linoleic acid isomers in beef fat

The amounts of 14 conjugated linoleic acid (CLA) isomers (t12t14, t11t13, t10t12, t9t11, t8t10, t7t9, t6t8; 12,14 c/t, t11c13, c11t13, t10c12, 9,11 c/t, t8c10, t7c9‐18:2) in 20 beef samples were determined by triple‐column silver‐ion high‐performance liquid chromatography (Ag⁺‐HPLC). Quantitation was performed using an external CLA reference standard consisting of cis9,trans11‐18:2,trans9,trans11‐18:2 and cis9,cis11‐18: 2. Linearity was checked as being r > 0.9999 between 0.02 × 10^‐3 to 2 mg/ml. The determination limit (5‐fold signal/noise ratio) of the CLA reference was estimated to be 0.25, 0.50, 1.0 ng/injection for the cis/trans, trans,trans and cis,cis isomers, respectively. As expected, cis9,trans11‐18:2 was the predominant isomer (1.95 ± 0.54 mg/g fat) in beef, followed by trans7,cis9‐18:2 (0.19 ± 0.04 mg/g fat); cis,cis isomers were below the determination limit in most beef samples. Total CLA amounts determined by Ag⁺‐HPLC were compared to total CLAs determined by gas chromatography (GC, 100 m CPSil^TM 88 column). The amounts obtained by GC were generally higher than those determined by Ag⁺ ‐HPLC due to co‐eluting compounds.     

Revisiting the formation of trans isomers during partial hydrogenation of triacylglycerol oils

The decisions to limit (Europe) or declare (USA) the trans isomer content of certain fatty foodstuffs have caused a demand for hardstocks with a reduced trans isomer content. One way to produce such hardstocks is by interesterifying high‐melting components such as palm stearin or fully hydrogenated vegetable oils with lauric or liquid oils. Another way is to modify the hydrogenation process. Possible modifications are reviewed. A moderate reduction in trans isomer content results from operating the hydrogenation process at much reduced temperature, but this also leads to an increase in saturates. Larger reductions in trans isomers may well be made possible by the recent development of new catalysts. One development involves the use of zeolites that allow the rather straight trans isomer to enter the pores while keeping the more curved cis isomers outside. The other development involves a precious metal catalyst that may have been modified in such a way that it has a reduced affinity for monounsaturated fatty acid moieties.     

Selective hydrogenation of sunflower seed oil in a three-phase catalytic membrane reactor

Continuous hydrogenation of sunflower seed oil has been carried out in a novel three-phase catalytic membrane hydrogenation reactor. The membrane reactor consisted of a membrane impregnated with Pd as the active catalyst, which provided a catalytic interface between the gas phase (H₂) and the oil. Hydrogenations were carried out at different pressures, temperatures, and selectivities, and the formation of trans isomers was monitored during the hydrogenation runs. For the three-phase catalytic membrane reactor, interfacial transport resistances and intraparticle diffusion limitations did not influence the hydrogenation reaction. Hydrogenation runs under kinetically controlled conditions showed that oleic and elaidic acid were not hydrogenated in the presence of linoleic acid. Initial formation of stearic acid was caused by direct conversion of linoleic acid into stearic acid by a shunt reaction. Furthermore, high selectivities led to high trans levels, which is in accordance with the many published data on hydrogenation of vegetable oils in slurry reactors. Finally, the catalytic membrane showed severe catalyst deactivation. Only partial recovery of the catalyst activity was possible.     

<Emphasis Type="Italic">Trans</Emphasis>-7,<Emphasis Type="Italic">cis</Emphasis>-9 CLA is synthesized endogenously by Δ<Superscript>9</Superscript>-desaturase in dairy cowsin dairy cows

Cis-9,trans-11 and trans-7,cis-9 CLA are the most prevalent CLA isomers in milkfat. The majority of cis-9,trans-11 CLA is synthesized endogenously by Δ⁹-desaturase. We tested the hypothesis that trans-7,cis-9 CLA originates from endogenous synthesis by inhibiting Δ⁹-desaturase with a source of cyclopropene FA (sterculic oil: SO) or with a trans-10,cis-12 CLA supplement. Experiment 1 (four cows; Latin square) involved four treatments: control, SO, partially hydrogenated vegetable oil (PHVO), and PHVO+SO. Milk, plasma, and rumen fluid were collected. Experiment 2 treatments (four cows) were 0 or 14.0 g/d of 10,12 CLA supplement; milk and plasma were collected. Samples were analyzed by GC and Ag⁺-HPLC to determine FA. In Experiment 1, SO decreased milkfat content of trans-7,cis-9 CLA by 68 to 71% and cis-9,trans-11 CLA by 61 to 65%. In Experiment 2, the 10,12 CLA supplement decreased milkfat content of trans-7,cis-9 CLA and cis-9,trans-11 by 44 and 25%, respectively. Correcting for the extent of treatment-induced inhibition of Δ⁹-desaturase based on changes in myristic and myristoleic acids, endogenous synthesis of trans-7,cis-9 CLA represented 85 and 102% in Experiments 1 and 2, respectively. Similar corrected values were 77 and 58% for endogenous synthesis of cis-9,trans-11 CLA. Thus, milkfat cis-9,trans-11 CLA was primarily from endogenous synthesis with a minor portion from rumen escape. In contrast, trans-7,cis-9 CLA was not present in rumen fluid in significant amounts. Results indicate this isomer in milkfat is derived almost exclusively from endogenous synthesis via Δ⁹-desaturase.