Synthesis of δ-eicosanolactone and δ-docosanolactone directly from meadowfoam oil

δ-Eicosanolactone and δ-docosanolactone were synthesized directly from the triacylglycerides of meadowfoam (Limnanthes) oil. Perchloric and sulfuric acids were used in stoichiometric quantities (0.5–4.0 mol equiv) to cyclize triglyceride to δ-lactone. When the reactions were run in the absence of solvent at 40°C, δ-lactone yields ranged from 17–75% where δ/γ ratios ranged from 6∶1 to 10.4.∶1. Sulfuric and perchloric acids gave similar yields for their individually optimized reactions. Perchloric acid-catalyzed reactions required less acid to produce similar amounts of δ-lactone (HClO₄ at 2.0 mol equiv gave 73% yield vs. H₂SO₄, which gave 75% yield at 2.5 mol equiv). The use of polar nonparticipating solvents during the reaction had little impact on δ-lactone formation or δ/γ ratio. Higher perchoric acid concentrations provided higher δ-lactone yields with δ/γ ratios remaining nearly constant. The effect of sulfuric acid on δ-lactone yield and δ/γ ratio was more direct; higher acid concentration improved, both. Both crystallization and short path distillation improved δ-lactone quality but short path distillation gave, higher recovered yields. The δ-lactones were converted to their corresponding 5-hydroxy acids in the same reaction vessel, separated, and cyclized back to δ-lactones upon heating under vacuum. This provided a convenient method for δ-lactone purification.     

5-Hydroxy fatty acid amides from δ-lactones and alkyl glucamines

δ-Lactones derived from unsaturated fatty acids are useful precursors to fatty amides due to their enhanced reactivity. Consequently, temperature-sensitive glucamines were easily converted to their 5-hydroxy fatty acid amides in high yield (52–97%) by reaction with C₁₈ and C₂₀ δ-lactones. High yields of amides (52–97%) were obtained with little or no solvent at 90°C in less than 24 h. C₁₈ δ-lactones were more miscible in the glucamine than the C₂₀ δ-lactones and thus increased reaction rates and yields of amides. In addition, amidation reactions run in the absence of catalyst gave good yields, whereas reactions in the presence of base catalysts completely inhibited the reaction. The 1-(N-alkyl-5-hydroxy fatty acid amido)-d-glucitols are expected to have useful properties as biodegradable components in detergents.     

Interaction Between Al-δ Layered Sodium Disilicate and Surfactant

This paper investigated the interaction of Al-δ-Na₂Si₂O₅ with surfactants (LAS, AOS, K12 and AEO-9) under condition approximating the detergent spray drying process. Al-δ-Na₂Si₂O₅ and the interaction samples were characterized by XRD, TG, FT-IR and Ca²⁺ ion binding capacity. The experimental results showed that Al-δ-Na₂Si₂O₅ might remain as δ phase after interacting with LAS. Al-δ-Na₂Si₂O₅ had changed to a mixed phase of δ phase and kanemite after interacting with K12 (or AEO-9, AOS). LAS provides protection for the Al-δ-Na₂Si₂O₅ structure and K12 also provides protection to Al-δ-Na₂Si₂O₅ though it changed to a mixed phase when /m _sur/m _solid was equal to 2:1:3. The m _sur/m _δ was equal to 0.5, interaction time was 60 min, temperature was 60 ± 2°C and the relative crystallinity of the above samples were 28 and 26% higher than that of blank (the sample without surfactant under the same experimental conditions), respectively. AEO-9 provided no obvious protection for the Al-δ-Na₂Si₂O₅ structure. AOS had destructive effect to the crystal structure of Al-δ-Na₂Si₂O₅ with δ phase relative crystallinity 10% lower than that of the blank under the same experiment condition.     

Optimal tocopherol concentrations to inhibit soybean oil oxidation

The optimal concentration for tocopherols to inhibit soybean oil oxidation was determined for individual tocopherols (α-, γ-, and δ-tocopherol) and for the natural soybean oil tocopherol mixture (tocopherol ratio of 1∶13∶5 for α-, γ-, and δ-tocopherol, respectively). The concentration of the individual tocopherols influenced oil oxidation rates, and the optimal concentrations were unique for each tocopherol. For example, the optimal concentrations for α-tocopherol and γ-tocopherol were ∼100 and ∼300 ppm, respectively, whereas δ-tocopherol did not exhibit a distinct concentration optimum at the levels studied (P<0.05). The optimal concentration for the natural tocopherol mixture ranged between 340 and 660 ppm tocopherols (P<0.05). The antioxidant activity of the tocopherols diminished when the tocopherol levels exceeded their optimal concentrations. Above their optimal concentrations, the individual tocopherols and the tocopherol mixture exhibited prooxidation behavior that was more pronounced with increasing temperature from 40 to 60°C (P<0.05). A comparison of the antioxidant activity of the individual tocopherols at their optimal concentrations revealed that α-tocopherol (∼100 ppm) was 3–5 times more potent than γ-tocopherol (∼300 ppm) and 16–32 times more potent than δ-tocopherol (∼1900 ppm).     

Authenticating Production Origin of Gilthead Sea Bream (<Emphasis Type="Italic">Sparus aurata)</Emphasis> by Chemical and Isotopic Fingerprinting

Recent EU legislation (EC/2065/2001) requires that fish products, of wild and farmed origin, must provide consumer information that describes geographical origin and production method. The aim of the present study was to establish methods that could reliably differentiate between wild and farmed European gilthead sea bream (Sparus aurata). The methods that were chosen were based on chemical and stable isotopic analysis of the readily accessible lipid fraction. This study examined fatty acid profiles by capillary gas chromatography and the isotopic composition of fish oil (δ¹³C, δ¹⁸O), phospholipid choline nitrogen (δ¹⁵N) and compound specific analysis of fatty acids (δ¹³C) by isotope ratio mass spectroscopy as parameters that could reliably discriminate samples of wild and farmed sea bream. The sample set comprised of 15 farmed and 15 wild gilthead sea bream (Sparus aurata), obtained from Greece and Spain, respectively. Discrimination was achieved using fatty acid compositions, with linoleic acid (18:2n-6), arachidonic acid (20:4n-6), stearic acid (18:0), vaccenic acid (18:1n-7) and docosapentaenoic acid (22:5n-3) providing the highest contributions for discrimination. Principle components analysis of the data set highlighted good discrimination between wild and farmed fish. Factor 1 and 2 accounted for >70% of the variation in the data. The variables contributing to this discrimination were: the fatty acids 14:0, 16:0, 18:0, 18:1n-9, 18:1n-7, 22:1n-11, 18:2n-6 and 22:5n-3; δ¹³C of the fatty acids 16:0, 18:0, 16:1n-7, 18:1n-9, 20:5n-3 and 22:6n-3; Bulk oil fraction δ¹³C; glycerol/choline fraction bulk δ¹³C; δ¹⁵N; % N; % lipid.     

Antioxidative stability of tempeh

Antioxidant activities of 6,7,4′-trihydroxyisoflavone and the compound 0.58 substance, (Rf value 0.58 on Silicagel TLC with cyclohexane 9 : ethylether 1) isolated from tempeh were measured by oxygen absorption. Both are active in preventing consumption of dissolved oxygen in an emulsified solution of safflower oil.     

Synergistic antioxidative effects of tocopherol and ascorbic acid in fish oil/lecithin/water system

Individual and combined effects of ascorbic acid andδ-tocopherol on the autoxidation of fish oil have been evaluated with the induction period monitored by Rancimat. The antioxidative efficiency of them was found to increase with increasing concentration.δ-Tocopherol and ascorbic acid acted highly synergistic with each other. Whenδ-tocopherol content was varied at a fixed content of ascorbic acid, the synergistic efficiency was generally 100% or more. On the other hand, when ascorbic acid content was varied at a fixed content ofδ-tocopherol, the synergistic efficiency rose sigmoidally with increasing concentration. We concluded that at least 0.01–0.02% ascorbic acid is required to obtain a considerable synergistic effect withδ-tocopherol in stabilizing fish oil.     

Quantitative analysis of long-chain trans-monoenes originating from hydrogenated marine oil

Gas chromatography (GC) is used for the analysis of trans-fatty acids in partially hydrogenated vegetable oils. Although trans-isomers of C₁₈ carbon length predominate in partially hydrogenated vegetable oils, trans-isomers of C₂₀ and C₂₂ carbon length occur in partially hydrogenated fish oil. We report a simple silver ion chromatographic combined with capillary GC technique for quantitative analysis of trans-monoenes derived from partially hydrogenated fish oil. Silver nitrate thinlayer chromatographic (TLC) plates are developed in toluene/hexane (50∶50, vol/vol). Fatty acid methyl esters are separated into saturates (R _f 0.79), trans-monoenes (R _f 0.49), cis-monoenes (R _f, 0.27), dienes (R _f, 0.10), and polyunsaturated fatty acids with three or more double bonds remaining at the origin. The isolated trans-monoenes are quantitatively analyzed by capillary GC. The technique of argentation TLC with GC analysis of isolated methyl esters is highly reproducible with 4.8% variation (i.e., coefficient of variation, CV%) in R _f values and 4.3 and 6.9% CV% in quantification within batch and between batch, respectively. Furthermore, the combined technique revealed that direct GC analysis underestimated the trans-content of margarines by at least 30%. In this study, C₂₀ and C₂₂ trans-monoenes were found in relatively large quantities; 13.9% (range 10.3–19.6%) and 7.5% (range 5.3–11.5%), respectively, in margarine purchased in 1995, but these C₂₀ and C₂₂ trans-monoenes were much reduced (0.1%) in a fresh selection of margarine purchased in 1998. Compositional data from labels underestimated the trans-content of margarines, especially those dervied from hydrogenated marine oil. Low levels of C₂₀ trans-monoenes (range 0.1–0.3%) and C₂₂ trans-monoenes (range 0.0–0.1%) were identified in adipose tissue obtained from healthy volunteers in 1995, presumably indicating consumption of partially hydrogenated fish oil.     

Oxidative Stability of Crude Mid-Oleic Sunflower Oils from Seeds with High γ- and δ-Tocopherol Levels

In this study, mid-oleic and high-oleic sunflower seeds were developed with high levels of γ- and δ-tocopherols by traditional breeding techniques. Sunflower seeds containing various profiles of tocopherols, ranging from traditional high α, low γ, low δ relative to those with high γ, high δ, and low α, were extracted, and the crude oil evaluated for oxidative stability. After aging at 60 °C, oils were measured for peroxide value and hexanal as indicators of oxidation levels. We found that when the γ-tocopherol content of mid-oleic sunflower oil (MOSFO) (NuSun) was increased from its regular level of 20 to 300–700 ppm, the oxidation of the oil was decreased significantly compared to MOSFO with its regular low γ-tocopherol level. The modified oils had α-tocopherol contents of up to 300 ppm without negatively affecting the stability of the oil. An oil with one of the best oxidative stabilities had a tocopherol profile of 470 ppm γ, 100 ppm δ, and 300 ppm α, indicating that MOSFO could be more oxidatively stable and still be a good source of Vitamin E from α-tocopherol. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.     

A critical evaluation of Raman spectroscopy for the analysis of lipids: Fatty acid methyl esters

The work presented here is aimed at determining the potential and limitations of Raman spectroscopy for fat analysis by carrying out a systematic investigation of C₄−C₂₄ FAME. These provide a simple, well-characterized set of compounds in which the effect of making incremental changes can be studied over a wide range of chain lengths and degrees of unsaturation. The effect of temperature on the spectra was investigated over much larger ranges than would normally be encountered in real analytical measurements. It was found that for liquid FAME the best internal standard band was the carbonyl stretching vibration ρ(C=O), whose position is affected by changes in sample chain length and physical state; in the samples studied here, it was found to lie between 1729 and 1748 cm⁻¹. Further, molar unsaturation could be correlated with the ratio of the ρ(C=O) to either ρ(C=C) or δ(H−C=) with R ²>0.995. Chain length was correlated with the δ(CH₂)_tw/ρ(C=O) ratio, (where “tw” indicates twisting) but separate plots for odd- and even-numbered carbon chains were necessary to obtain R ²>0.99 for liquid samples. Combining the odd- and even-numbered carbon chain data in a single plot reduced the correlation to R ²=0.94–0.96, depending on the band ratios used. For molal unsaturation the band ratio that correlated linearly with unsaturation (R ²>0.99) was ρ(C=C)/δ(CH₂)_sc (where “sc” indicates scissoring). Other band ratios show much more complex behavior with changes in chemical and physical structure. This complex behavior results from the fact that the bands do not arise from simple vibrations of small, discrete regions of the molecules but are due to complex motions of large sections of the FAME so that making incremental changes in structure does not necessarily lead to simple incremental changes in spectra.     

Purity assessments of major vegetable oils based on δ13C values of individual fatty acids

The fatty acid compositions and δ¹³C values of the major fatty acids of more than 150 vegetable oils were determined to provide a database of isotopic information for use in the authentication of commercial maize oil. After extraction of oils from seeds, nuts or kernels, and methylation, fatty acid compositions were determined by capillary gas chromatography. All compositions were within the ranges specified by the Codex Alimentarius. Gas chromatography combustion-isotope ratio mass spectrometry was employed to determine the δ¹³C values of the major fatty acids of the oils. A large number of pure maize oils and potential adulterant oils from various parts of the world were studied to assess the sources of variability in δ¹³C values. Such information is vital to establishing the compound specific isotope technique as a reliable means of assessing vegetable oil purity. Variability in δ¹³C values was related to the geographical origin of the oil, year of harvest, and the particular variety of oil. This suggests that the ultimate δ¹³C values of fatty acids are determined by a combination of environmental and genetic factors.     

Fractal scaling of soot packing density across five size decades

We experimentally map the scaling laws for packing density (θ_f, solid component volume fraction) of soot aggregates across five orders of magnitude of size (R_g/a, normalized radius of gyration by monomer radius). The θ_f ? R_g/a scaling relationship evolves through three successive regimes with distinct power-law exponents of ?1.20 ± 0.01, ?0.58 ± 0.06, and ?1.31 ± 0.14. The first cross-over agrees with the classical aerosol-to-gel transition theory. This agreement, however, breaks down at the second cross-over point, where a late-stage cluster-cluster aggregation of aerosol gels takes over.

© 2017 American Association for Aerosol Research     

Occurrence of geometrical isomers of eicosapentaenoic and docosahexaenoic acids in liver lipids of rats fed heated linseed oil

Monotrans geometrical isomers of 20∶5 n−3 and 22∶6 n−3 were detected in liver lipid of rats fed heated linseed oil. The isomers were identified as being 20∶5 δ5c, 8c, 11c, 14c, 17t and 22∶6 δ4c, 7c, 10c, 13c, 16c, 19t. These fatty acids were isolated as methyl esters by preparative high-performance liquid chromatography (HPLC) on reversed phase columns followed by silver nitrate thin layer chromatography (AgNO₃-TLC). The structures were identified using partial hydrazine reduction, AgNO₃-TLC of the resulting monoenes, oxidative ozonolysis of each monoene band, and gas-liquid chromatography (GLC) of the resulting dimethyl esters and monomethyl esters. Fourier-transform-infrared spectrometry confirmed thetrans geometry in isolated 20∶5 and 22∶6 isomers. The isomers of eicosapentaenoic and docosahexaenoic acids in liver lipids probably resulted from desaturation and elongation of 18∶3 δ9c, 12c, 15t, a geometrical isomer of linolenic acid present in the heated dietary oil.     

The rate of ring opening of γ-and δ-lactones derived from meadowfoam fatty acids

δ-Lactones derived from meadowfoam (Limnanthes) fatty acids were reacted with amine and alcohol nucleophiles in a second-order reaction to provide the acyclic 5-hydroxy eicosanoic acid esters and amides. The rate of reaction for the ring opening of δ-lactones was compared to the rate of ring opening of γ-lactones and the rate of derivatization of meadowfoam fatty acids. δ-Lactones showed a much larger rate for the formation of derivatives than the corresponding γ-lactones or fatty acids. γ-Lactone had a rate constant >7700 times larger for the formation of butyl ester than meadowfoam fatty acids. The formation of amides from δ-lactones is even faster than the esterification reaction and requires no catalyst or solvent when conducted at the melting point of the lactone.     

Natural abundance stable carbon isotope evidence for the routing and <Emphasis Type="Italic">de novo</Emphasis> synthesis of bone FA and cholesterol

This research reported in this paper investigated the relationship between diet and bone FA and cholesterol in rats raised on a variety of isotopically controlled diets comprising 20% C₃ or C₄ protein (casein) and C₃ and/or C₄ nonprotein or energy (sucrose, starch, and oil) macronutrients. Compoundspecific stable carbon isotope analysis (δ¹³C) was performed on the FA (16∶0, 18∶0, 18∶1, and 18∶2) and cholesterol isolated from the diet (n=4) and bone (n=8) of these animals. The dietary signals reflected by the bone lipids were investigated using linear regression analysis. δ¹³C values of bone cholesterol and stearic (18∶0) acid were shown to reflect whole-diet δ¹³C values. whereas the δ¹³C values of bone palmitic (16∶0), oleic (18∶1), and linoleic (18∶2) acids reflected dietary FA δ¹³C values. Dietary signal differences are a result of the balance between direct incorporation (or routing) and de novo synthesis of each of these bone lipids. Estimates of the degree of routing of these bone lipids gleaned from correlations between Δ¹³C _dlipid-wdiet (δ¹³C_{diet lipid}-δ¹³C_{whole diet}) spacings and Δ¹³C _blipid-wdiet (δ¹³C_{bone lipid}-δ¹³C_{whole diet} fractionations demonstrated that the extent of routing, where 18∶2>16∶0>18∶1>18∶0>cholesterol, reflected the relative abundances of these lipids in the diet. These findings provide the basis for more accurate insights into diet when the δ¹³C analysis of bone fatty FA or cholesterol is employed.     

Castor oil and PEG‐based shape memory polyurethane films for biomedical applications

A series of polyurethane film were prepared from poly(ethylene glycol) with different molecular weight (PEG 1500, 3000, and 8000) and castor oil by one‐shot bulk polymerization method. Hexamethylene diisocyanate and 1,4‐buthane diol were used as diisocyanate and chain extender, respectively. In order to characterize the samples, their density, swelling ratio, water contact angle, surface free energy, gel content, thermal, and viscoelastic properties were determined. The effect of the soft segment length (SSL) and hard segment content (HSC) of all polyurethane films on their shape memory behavior such as shape fixity (R_f) and shape recovery (R_r) rates were investigated by bending test. Direct contact and MTT tests were used for assessment of cell adhesion and proliferation. The relatively high R_f and R_r values were obtained for the samples programmed at high temperature difference. R_f increased with decreasing HSC. On the other hand, R_r tended to decrease with increasing SSL. After evaluating experimental data by a nonlinear equation, it was found that HSC is more effective parameter on shape memory property than SSL. The gel content, swelling ratio, and water contact angle of the samples were dependent on both SSL and HSC in their structures. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40590.     

Cytotoxicity of tocopherols and their quinones in drug-sensitive and multidrug-resistant leukemia cells

Cytotoxicities of tocopherols (α-T, γ-T, δ-T), their para (α-TQ, γ-TQ, δ-TQ)-and ortho (Tocored)-quinone oxidation products, the synthetic quinone analog of γ-TQ containing a methyl group substituted for the phytyl side-chain (TMCQ) and the synthetic quinone analog of Tocored containing a methyl group substituted for the phytyl side-chain (PR) were measured in acute lymphoblastic leukemia cell lines that are drug-sensitive (CEM) and multidrug-resistant (CEM/VLB₁₀₀). Among tocopherols, only δ-T exhibited cytotoxicity. Among para quinones, α-TQ showed no cytotoxicity, while γ-TQ and δ-TQ were highly cytotoxic in both CEM and CEM/VLB₁₀₀ cell lines (LD₅₀<10 μM). δ-TQ and γ-TQ were more cytotoxic than the widely studied chemotherapeutic agent doxorubicin, which also showed selective cytotoxicity to CEM cells. The orthoquinone Tocored was less cytotoxic than doxorubicin in drug-sensitive cells but more cytotoxic than doxorubicin in multidrug-resistant cells. Cytotoxicity was not a function of the phytyl side-chain since both TMCQ and PR were cytotoxic in leukemia cells. Cytotoxic para and ortho quinones were electrophiles that formed adducts with nucleophilic thiol groups in glutathione and 2-mercaptoethanol. Cytotoxicity was enhanced when the glutathione pool was depleted by preincubation with buthionine-[S,R]-sulfoximine, but cytotoxicity was diminished by the addition of N-acetylcysteine to cultures. α-T also diminished the cytotoxicity of para- and or-thoquinones. Buthionine-[S,R]-sulfoximine did not block the inhibitory effect of either N-acetylcysteine or α-T, showing that these agents did not act solely by maintaining the glutathione pool as an essential antioxidant system. In conclusion, tocopherylquinones represent a new class of alkylating electrophilic quinones that function as highly cytotoxic agents and escape multidrug resistance in acute lymphoblastic leukemia cell lines.     

Prediction of adipose tissue composition using raman spectroscopy: Average properties and individual fatty acids

Raman spectroscopy has been used for the first time to predict the FA composition of unextracted adipose tissue of pork, beef, lamb, and chicken. It was found that the bulk unsaturation parameters could be predicted successfully [R ²=0.97, root mean square error of prediction (RMSEP)=4.6% of 4 δ], with cis unsaturation, which accounted for the majority of the unsaturation, giving similar correlations. The combined abundance of all measured PUFA (≥2 double bonds per chain) was also well predicted with R ²=0.97 and RMSEP=4.0% of 4 δ. Trans unsaturation was not as well modeled (R ²=0.52, RMSEP=18% of 4 δ); this reduced prediction ability can be attributed to the low levels of trans FA found in adipose tissue (0.035 times the cis unsaturation level). For the individual FA, the average partial least squares (PLS) regression coefficient of the 18 most abundant FA (relative abundances ranging from 0.1 to 38.6% of the total FA content) was R ²=0.73; the average RMSEP=11.9% of 4 δ. Regression coefficients and prediction errors for the five most abundant FA were all better than the average value (in some cases as low as RMSEP=4.7% of 4 δ). Cross-correlation between the abundances of the minor FA and more abundant acids could be determined by principal component analysis methods, and the resulting groups of correlated compounds were also well predicted using PLS. The accuracy of the prediction of individual FA was at least as good as other spectroscopic methods, and the extremely straightforward sampling method meant that very rapid analysis of samples at ambient temperature was easily achieved. This work shows that Raman profiling of hundreds of samples per day is easily achievable with an automated sampling system.     

Quantitative analysis of partial acylglycerols and free fatty acids in palm oil by 13C nuclear magnetic resonance spectroscopy

The chemical shifts, spin-lattice relaxation times (T ₁), and one-bond C−H coupling constants of the glycerol carbons of mono-, di-, and triacylglycerols in CDCI₃ solution are presented and discussed. The glycerol carbons have low T ₁ values (<1.0 s) and full nuclear Overhauser effect and also exhibit broader linewidths than the aliphatic carbons, suggesting that the glycerol carbons are at or near the T ₁ minimum for the dipole-dipole relaxation mechanism. Therefore, for quantitative measurement of the composition of partial acylglycerols (relative to the triacylglycerols) in palm oil, the nuclear magnetic resonance (NMR) spectrum of the β-carbons, which lie exclusively in the region δ68.3–72.1 ppm, should preferably be acquired at medium or low magnetic fields and at an elevated temperature in order to ensure that the condition for extremely narrow spectral lines is satisfied. The chemical shifts and spinlattice relaxation times of the aliphatic C-2 and C-3 carbons and of the carbonyl carbons (C-1) of acyl groups present in palm oil are also presented and discussed. The presence of free fatty acid in the palm oil is easily detected and quantified in the spectrum of the aliphatic carbons. The presence of partial acylglycerols in palm oil can also be detected and/or quantified in the NMR spectra of the C-2 and the carbonyl carbons. The quantitative analysis of the glycerol carbons of a known mixture of acylglycerols obtained by using this method is presented.     

Electrochemical characterization of perovskite-based SOFC cathodes

The electrochemical performance of La_0.58Sr_0.4Co_0.2Fe_0.8O_3-δ (L58SCF), La_0.78Sr_0.2Co_0.2Fe_0.8O_3-δ (L78SCF) and composite La_0.65Sr_0.3MnO_3-δ – 8 mol% Y₂O₃ stabilized ZrO₂ (LSM-YSZ, 50:50 wt%) cathode electrodes interfaced to a double-layer electrolyte made of Ce_0.8Gd_0.2O_2-δ (CGO) and YSZ was studied in the temperature range 600–850 °C using impedance spectroscopy and current-overpotential measurements. The experiments were carried out in a single chamber cell using a three electrode set-up with porous Pt films as auxiliary electrodes. The perovskite powders were synthesized using the spray-drying technique starting from nitrate precursors and were deposited on the solid electrolyte via screen-printing. Open circuit impedance measurements on as-prepared electrodes, i.e. before any polarization, and micropolarization measurements have shown that the L78SCF/CGO/YSZ electrode exhibits the lowest area specific polarization resistance R _F (R _F was approximately equal to 0.4 Ω cm² at 800 °C and = 21 kPa) or, equivalently, the highest electrocatalytic activity according to the order: LSM/LSM-YSZ/CGO/YSZ<L58SCF/CGO/YSZ<L78SCF/CGO/YSZ. Current-overpotential data taken over an extended cathodic overpotential (ohmic-drop-free) range (0 to −500 mV) also indicated the aforementioned order of electrocatalytic activity. The Nyquist plots corresponded to at least two overlapping arcs or, equivalently, to at least two rate limiting processes. The relative contribution and degree of overlap of these arcs depended on electrode material, temperature and oxygen partial pressure, the low frequency arc being in general dominant at low temperatures and low oxygen partial pressures. Open circuit impedance experiments carried out at different oxygen partial pressures (0.01–100 kPa) revealed an exponential increase of the open-circuit area specific polarization conductance with increasing .