Accurate determination of trans isomers in shortenings and edible oils by infrared spectrophotometry

A Fourier transform infrared spectroscopy procedure is described for quantitating the levels of total trans triglycerides or their fatty acid methyl ester derivatives in neat fats and oils. It requires either warming or no preparation of the laboratory sample, and about 5 rain for spectroscopic measurement, band area integration, and calculation of the trans content from a linear regression equation, q-o eliminate the strongly sloping background of the 966-cm -I trans band, the single-beam spectrum of the trans-containing fat is "ratioed" against that of an unhydrogenated oil or a reference material that contains only cis double bonds. Thus, a symmetric absorption band on a horizontal background is obtained. The area under the trans band can then be accurately integrated between the same limits, 990 and 945 cm -1, for all trans levels investigated. To speed up the analysis, an attenuated total reflection liquid cell was used, into which oils, melted fats or their methyl esters were poured without weighing or quantitative dilution with the toxic and volatile carbon disulfide solvent. The trans levels determined by attenuated total reflection were closer to those found by capillary gas chromatography when the hydrogenated fat was measured against the corresponding unhydrogenated oil than when it was measured against a cis reference material. Small differences were found between trans levels in hydrogenated fat test samples and the corresponding methyl ester derivatives (9.3 and 2.2% at about 2 and 41% trans, respectively). The lower limits of identification and quantitation were 0.2 and 1%, respectively.

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Rapid determination of the totaltrans content of neat hydrogenated oils by attenuated total reflection spectroscopy

Mossoba

Yurawecz

McDonald

1996

“…The determination of total trans fatty acids by infrared spectroscopy (IR) has been widely used for many decades (1). To improve the accuracy of the IR methods (2,3), many modifications have been proposed since the 1960s (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15), including refinements recently introduced by two new IR Official Meth-ods that were adopted by the Association of Official Analytical Chemists (AOAC) in 1994 (16) and the American Oil Chemists' Society (AOCS) in 1995 (17). The basis of the IR determination stems from the fact that the C-H out-of-plane deformation band, observed at 966 cm −1 , is uniquely characteristic of isolated double bonds with trans configuration.…”

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confidence: 99%

Determination of trans fatty acids in hydrogenated vegetable oils by attenuated total reflection infrared spectroscopy: Two limited collaborative studies

Adam¹,

Chew²,

Wasserman³

et al. 1998

An attenuated total reflection infrared spectroscopy procedure was collaboratively studied among two sets of five laboratories for quantitating the total trans fatty acid levels in neat (without solvent) hydrogenated vegetable oils, measured as triacylglycerols in one study, and as fatty acid methyl ester derivatives in the other. Unlike the fatty acid methyl esters, the triacylglycerols required no derivatization but had to be melted prior to measurement. To obtain a symmetric absorption band at 966 cm −1 on a horizontal background, the singlebeam spectrum of the trans-containing fat was "ratioed" against that of a refined oil or a reference material that contained only cis double bonds. A single-bounce horizontal attenuated total reflection cell that requires 50 µL of undiluted test samples was used for oils, melted fats, or their methyl esters. For fatty acid methyl esters, the reproducibility relative standard deviations were in the range of 0.9 to 18.46% for 39.08 to 3.41% trans, determined as methyl elaidate per total fatty acid methyl esters. For five pairs of triacylglycerol blind duplicates, the reproducibility and repeatability relative standard deviations were in the ranges of 1.62 to 18.97%, and 1.52 to 13.26%, respectively, for 39.12 to 1.95% trans, determined as trielaidin per total triacylglycerols. Six pairs of spiked triacylglycerol blind duplicates (quality assurance standards) exhibited high accuracy in the range of 0.53 to 40.69% trans and averaged a low bias of 1.3%. These statistical analysis results were compared to those collaboratively obtained by the recently adopted AOCS Cd14-95 and AOAC 994.34 Infrared Official Methods. JAOCS 75, 353-358 (1998).

“…For the quantitative determination of the cis-trans isomer ratio [13][14][15], the methyl esters obtained were dried under an N 2 atmosphere and then injected into a liquid Fourier-transform infrared (FTIR) ZnSe cell using a Nicolet 470 spectrometer equipped with a computer [1]. The IR spectra at 2 cm -1 resolutions in the range from 3,200 to 800 cm -1 with 32 scans were collected.…”

Section: Measurementsmentioning

confidence: 99%

Effect of Ru Nanoparticle Size on Hydrogenation of Soybean Oil

Liew

2006

Four Ru nanoparticles of different mean sizes from 1.13 to 17.22 nm were prepared and used as catalysts for the selective hydrogenation of polyunsaturated soybean oil at 353 K and initial pressure of 1.5 MPa. The catalyst with the smallest mean size (1.13 nm) had the lowest activity, the activity increased as the mean size increased to 3.10 nm, then decreased with further increase in the mean particle size. The cis-trans isomerization rate decreased with the increase in particle size.