Infrared absorption of methylcis-9,trans-11-, andtrans-10,cis-12-octadecadienoates

The ratio of absorptivity at 10.2 µm and 10.6 µm differs between methylcis-9,trans-11-, andtrans-10,cis-12-octadecadienoates. For thecis-9,trans-11-ester, a_10.2 µm/a_10.6 µm is in the range of 1.1–1.2; for thetrans-10,cis-12-ester, it is 1.3–1.4. These differences in absorptivities are great enough to affect significantly compositions calculated from IR absorption.     

Comparison of FTIR and capillary gas chromatographic methods for quantitation oftrans unsaturation in fatty acid methyl esters

A computer-assisted method has been developed for estimation of isolatedtrans unsaturation using the peak area of thetrans absorbance band at 966 cm-1from FTIR spectra of fatty acid methyl esters. Peak areas were used to determine thetrans content of weighed standards containing from 0 to 100% methyl elaidate and of hydrogenated soybean oil samples containing up to 36%trans unsaturation. These data for percenttrans by FTIR were compared to corresponding data obtained by capillary gas chromatography and the AOCS Official Method 14-61. Determination of isolatedtrans composition in oils using peak areas gave values with the smallest standard deviation for weighed standards and values within 4% of those obtained by capillary gas chromatography and the AOCS Official Method for hydrogenated samples. Presented at the AOCS meeting in Phoenix, AZ in May 1988. To whom correspondence should be addressed.     

The determination ofTrans isomers in GLC fractions of unsaturated esters

The determination of the amount oftrans unsaturated isomers present in collected fractions of unsaturated fatty acid methyl esters separated by gas liquid chromatography is accomplished by measuring the infrared absorbances of the collected peak at 10.36 and 8.55 μ. The ratio of these two absorbances is proportional to thetrans unsaturation. The interfering polyester column bleed is removed from the collected peaks by collection on alumina and elution into the spectrophotometer cell with CS₂.     

A rapid method for the estimation oftrans unsaturation in hydrogenated oils and fats

Glycerides and methyl esters of fatty acids containingtrans unsaturation both show peaks at 10,38 μ. The absorptivities of the glycerides (a_10.38 μ) have a straight line relationship with the concentration of thetrans unsaturation, calculated as methyl elaidate. This relationship has been utilized as a quick method for estimating thetrans unsaturation in hydrogenated fats such as Vanaspati. The infrared spectrum of a given hydrogenated fat is taken in the region of 9–11 μ, the absorptivity at thetrans-peak is calculated, and the corresponding methyl elaidate content is read from a graph.     

Determination ofcis unsaturation in oils by near infrared spectroscopy

An analytical method has been developed capable of giving reproducible and accurate determinations of thecis unsaturation present in refined oils, hydrogenated oils, and finished shortenings. Molar absorptivity measurements indicate that similar methods are applicable to the analyses of mixed esters or fatty acids. The method depends upon the measurement of a band in the near infrared at 2.143 μ that is caused bycis unsaturation. The following pertinent conclusions are drawn from data obtained in this investigation.

1. The areas under the absorption bands forcis polyenes are integral multiples of the areas under the bands ofcis monoenes.
2. Thecis content of oils containing less than 10%trans triglycerides can be determined accurately by measuring the area under the absorption band.
3. Accurate results can be obtained for samples containing quantities oftrans fatty acids in excess of 10% if a point baseline is used and the peak absorbance measured.

     

Direct determination oftrans unsaturation in triglycerides by infrared spectrophotometry

A differential infrared spectrophotometric method is described for the determination oftrans unsaturation in fats. The method utilizes absorption at 965 cm⁻¹, due to the C−H out-of-plane deformation vibrations oftrans unsaturated compounds. The method is rapid, accurate, and directly applicable to the determination oftrans unsaturation in triglycerides. It is applicable to samples which contain low concentrations oftrans acids (down to 2%) and also to samples with fatty acids of mixed chain length.     

Regulatory Infrared Spectroscopic Method for the Rapid Determination of Total Isolated Trans Fat: A Collaborative Study

Using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, collaborating scientists in ten different laboratories measured (in duplicate) the total trans fat content of ten fat or oil test samples, two of which were blind duplicates. The procedure used entailed measuring the height of the negative second derivative of the IR absorption band at 966 cm^?1. This absorption is attributed to the C?CH deformation vibration that is characteristic of isolated (non-conjugated) double bonds with the trans configuration. The precision of ATR-FTIR results in this international collaborative study was satisfactory and led to the approval of this validated procedure as official method AOCS Cd 14e-09 in late 2009. This official method is also suitable for analysis of total isolated trans fat and oil products containing, or supplemented with, trans conjugated linoleic acid (CLA) isomers. Although this method does not require derivatization of the oil or fat test materials, as required for GC, fats and oils in foods must be extracted with organic solvents before analysis. This method is also rapid (5 min) and does not require any weighing or quantitative dilution of unknown neat fat or oil test samples in any solvent. The AOCS Cd 14e-09 method is suitable for determination of test samples with zero trans fat, which is defined according to the US labeling regulations as 0.5 g trans fat per serving or 1.8% trans fat, as a percentage of total fat.     

Physicochemical Properties of Conjugated Linoleic Acid-Rich Soy Oil

CLA-rich soy oil (CLARSO) has been produced by linoleic acid isomerization in soy oil TAG. The objective was to determine the physicochemical properties of the novel CLARSO relative to conventional refined bleached deodorized soy oil (RBDSO). Iodine value decreased in CLARSO samples despite unsaturation being unchanged, probably because conjugated double bonds in triacylglycerol (TAG) of CLARSO impede the complete addition of iodine. Thermal analysis by differential scanning calorimetry showed the melting point temperature increased with the increase in the CLARSO CLA concentration, and melting point broadening occurred in CLA contained samples. Dynamic viscosity of CLARSO conducted from 4 to 44 °C increased with the increase in CLA concentration, relative to RBDSO. Greatest viscosity differences occurred at the lower temperatures. Refractive indices and density were not greatly affected. The change in physical properties was attributed to the increased intermolecular hydrophobic interaction force due to conjugated double bonds and trans,trans isomers, relative to RBDSO. This may provide hard fat characteristics that may be useful for use in producing margarine or shortenings. Furthermore, the higher viscosity at refrigerator temperatures may be useful in salad oil and refrigerated sauces to enable suspension of particles and maintain a rich, thicker texture.     

The application of packed column gas chromatographic analysis to the determination oftrans unsaturation

A study of the separation of synthetic mixtures ofcis andtrans methyl octadecenoate with packed column gas chromatography indicated its usefulness for such analyses. Several margarines were analyzed by this method and the results compared with those obtained by the infrared spectroscopic method. Reasonable agreement between both methods was obtained, but the gas chromatographic determination yielded lower values (average 3.8%). The presence oftrans unsaturation was also shown in selected samples of human milk and blood lipids.     

Homogeneous catalytic hydrogenation of unsaturated fats: Iron Pentacarbonyl

Iron pentacarbonyl is an effective homogeneous catalyst for the reduction of polyunsaturated fats. Hydrogenation of soybean oil and its methyl esters has been achieved at 180C, hydrogen pressures of 100-1,000 psi, and 0.05–0.5 molar concentrations of catalyst. Analyses of partially reduced products show considerable isomerization of double bonds, reduction of linolenate and linoleate with little or no increase in stearate, and accumulation ofcis,trans- andtrans, trans-conjugated dienes, and isolatedtrans monoenes. The unreduced trienes include diene conjugated fatty esters. The nonconjugated dienes contain large amounts oftrans and nonalkali conjugatable unsaturation. Considerable scattering of double bonds is evident in different fractions between the C₄ and C₁₆ positions. Complex formation between iron carbonyl and unsaturated fats is also indicated. The course of the homogeneous hydrogenation catalyzed by iron pentacarbonyl appears similar to the heterogeneous catalytic reaction. Metal carbonyls are well known for their isomerizing effects and their ability to form stable complexes with olefins. These homogeneous complexes provide suitable model systems to study the mechanism of catalytic hydrogenation of fats.     

Comparison of fatty acid composition of domestic and imported margarines and frying fats in Bulgaria

A total of 82 dietary fats sold on the Bulgarian market in the period 1995—2000 were analyzed. The samples included 68 table margarines (50 of which were imported), 10 frying fats (6 imported) and 4 salad dressings (all imported). A validated analytical method, thin‐layer chromatography‐AgNO₃‐densitometry, was used. It enabled direct determination of all fatty acid groups, differing by degree of unsaturation and double bonds geometry. Low levels of trans fatty acids (TFA) down to 0.1% of the total for mono trans‐trienoic (Tcct) and mono trans‐dienoic (Dct), and down to 0.2% for trans‐monoenoic (Mt) were quantitated, with an error under 3% and a standard deviation of 0.1—1.5. The total content of TFA in table margarines varied from 0 to 26.9% with a mean value of 8.6 ± 7.2% for imported and 1.6 ± 3.4% for Bulgarian samples. Saturated fatty acids (SFA) content varied from 11.5 to 45.7%, with a mean value of 25.4 ± 5.7% for imported and 26.9 ± 5.2% for Bulgarian margarines. A general trend of lower levels of TFA and SFA in imported margarines was observed over the studied period. Additionally, the content of individual saturated fatty acids was determined by gasliquid chromatography in 37 of all studied samples.     

A rapid method for the analysis of hydrogenated fats by GC with IR detection

A rapid method for analysis of trans and cis FA in hydrogenated fats has been developed. The method is based on a single anlaysis by CG with IR detection. Multivariate partial least squares regression is applied on the IR spectra to predict the number of cis and trans double bonds. For each chain length the method provides information about the amount of the saturated FA, the amount of trans monoenes, the amount of cis monoenes, the amount of PUFA, and the average number of cis and trans double bonds in PUFA. The method has been validated by summing the values to a total trans value and total unsaturation. These sum values were compared with total trans unsaturation, as determined by AOCS method Cd 14-95, and iodine value, as determined by AOCS Cd 1d-92.     

Titration of sterol double bonds with dibromopyridine sulfate

Cis andtrans-22-dehydrocholesteryl acetates andcis andtrans-22-cholesten-3β-yl acetates were prepared and compared to Δ²²-phytosteryl acetates by titration with dibromopyridine sulfate. The cholesterol derivatives absorbed close to the theoretical quantity of bromine (1 Br₂ per double bond), whereas the Δ²²-C₂₄-alkylated sterols consumed 0.14 to 0.23 Br₂ in excess of the calculated values. This excess is attributed to the formation of additional unsaturation during bromination. Δ⁷ and Δ⁸⁽¹⁴⁾-sterols consume more than 2 and 3 moles Br₂, respectively, which indicates that at least one or two new double bonds are formed in these molecules during the bromination step. Arizona Agricultural Experiment Station Journal Article No. 2664.     

Spectral confirmation of trans monounsaturated C18 fatty acid positional isomers

The trans octadecenoic acid methyl ester isomers were obtained from a partially hydrogenated soybean oil sample and isolated by silver-ion high-performance liquid chromatography. The double bond configuration was confirmed to be trans by using gas chromatography-direct deposition-Fourier transform infrared spectroscopy. The double bond positions for nine individual trans octadecenoic acid positional isomers were confirmed by gas chromatography-electron ionization mass spectrometry after derivatization to 2-alkenyl-4,4-dimethyloxazoline. These nine trans positional isomers were resolved on either one of the two polar 100% cyanopropylpolysiloxane 100-m capillary columns, SP 2560 and Cp-Sil 88, at an isothermal temperature of 140°C. These nine isomers were confirmed to have double bonds at carbons C-8 through C-16. The pair of trans octadecenoic acid positional isomers with double bonds at C-13 and C-14 are reported for the first time to be resolved by gas chromatography. This work was presented in part at the 87th American Oil Chemists’ Society Annual Meeting in Indianapolis, IN, April 28–May 1, 1996.     

Rheological and Microscopic Properties of Fat Blends with Similar Solid Fat Content but Different Trans Composition

In this study, two different groups of fat samples were prepared in a way that samples of each group had different trans fatty acid (TFA) composition but similar solid fat content (SFC). Samples of the first group (named group A) had TFA between 0.0 and 56.23 %, while the samples of the second group (group B) contained trans isomers ranging from 0.0 to 44.4 %. A polarized microscope was used to monitor the differences between the samples in terms of crystal size and crystal number during isothermal crystallization. In general, increasing TFA resulted in formation of larger crystals in a shorter time. Similar findings were also observed when small deformation time and frequency sweep experiments were conducted. A higher TFA content led to higher complex modulus values during isothermal crystallization. On the other hand, when the samples were stored at 4 °C for 48 h, the samples with the lower trans isomer had higher hardness values.     

Poly(ethylene-co-vinyl alcohol-co-vinyl mercaptoacetate) (EVALSH)-determination of the vinyl mercaptoacetate content by thermogravimetric analysis and FTIR spectroscopy

Summary A quantitative method for the determination of vinyl mercaptoacetate (VMA) in poly(ethylene-co-vinyl alcohol-co-vinyl mercaptoacetate) (EVALSH) based on Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) was developed. A plot of relative absorbance values (A₁₇₃₆/A₇₂₀) versus esterification degree in EVALSH samples determined by TGA analysis revealed a good linear relationship.     

Synthesis,Characterization, and Application of Zn–Al Layered Double Hydroxide as a Nano-Sorbent for the Removal of Direct Red 16 from Industrial Wastewater Effluents

In this research, nano-structured zinc–aluminum layered double hydroxide (Zn–Al LDH) was successfully synthesized by a co-precipitation method and followed by thermal treatment. The structure and morphology of the obtained material was characterized by X-ray diffraction, transmission electron microscopy, nitrogen-adsorption–desorption isotherms, and Fourier transform infrared spectroscopy. The as-prepared LDH was applied as a solid phase extraction (SPE) sorbent for the removal of direct red 16 (DR16) from aqueous solutions. A spectrophotometric method was used for monitoring of the extracted DR16 at λ = 548 nm. The effect of several parameters such as pH, sample flow rate, amount of nano-sorbent, elution conditions, and sample volume on the removal percentage was investigated. The results showed that DR16 could be retained by Zn–Al(NO₃^?) LDH at pH 6 and stripped by 2.5 mL of 1.0 mol L^?1 NaOH. In the optimum experimental conditions, the limit of detection and relative standard deviation were 0.003 µg mL^?1 and 1.2%, respectively. The calibration graph using the presented SPE system was linear in the range of 0.01–2.00 µg mL^?1 of DR16 with a correlation coefficient of 0.9994. The method was successfully applied for the removal of DR16 from several industrial wastewater effluents.     

Cis and trans components of lipids: Analysis by 1H NMR and silver shift reagents

In this study, the methodology of shift reagents was exploited to distinguish cis and trans unsaturation in oils and fats. The differential binding of silver ions (in the form of AgFOD) to cis and trans double bonds allowed the separation of the allylic and olefinic proton signals in the ¹H NMR spectra of mixtures of cis and trans methyl esters of monoene aliphatic acids and unsaturated triacylglycerol mixtures at low frequency spectrometers (300 MHz). Careful integration of the appropriate proton resonances in the recorded quantitative ¹H NMR spectra afforded percentage concentrations in very good agreement with the actual values. This ¹H NMR methodology was validated by analyzing AOCS Laboratory Proficiency Program GC samples containing various percentages of saturated, cis‐mono unsaturated, and cis‐polyunsaturated fat as well as trans content. This fast and relatively low‐cost NMR methodology could be used on line for obtaining nutrition labeling compositional data (NLCD) required for fat‐containing food products. Attempts to differentiate lipid molecules with different degree of unsaturation and positional distribution of cis double bonds were unsuccessful.     

Large temperature coefficient of resistance at near room temperature in Sr-doped La0.72Ca0.28MnO3:Ag0.2 polycrystalline composites

A series of La_0.72Ca_0.28?xSr_xMnO₃:Ag_0.2 (x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.10) composites was prepared by sol–gel method using methanol as solvent. Sample composition was analyzed by X-Ray diffraction, which revealed that all samples are pseudo-perovskite. Grain size and morphology were characterized by scanning electron microscopy. The results showed that all samples are of high density and large grain size in the range of 50–100 µm. All samples exhibited sharp metal–insulator (M-I) transitions, along with a drastic transition from paramagnetism to ferromagnetism. With increased Sr doping, radius of A-site ion increased, both Curie temperature T_C and M-I transition temperature shift to higher temperature increases, and transition width turns widener which makes a decreased temperature coefficient of resistance (TCR). Larger ionic radius of Sr²⁺, which resulted in enhancement of double exchange, enlarges Mn–O–Mn bond angle, hence improves electrical and magnetic properties. It was found that TCR could reach 24.3% K^?1 by Ag addition at near room temperature, which makes this composite promising potential applications in infrared detection and night vision.