Anal. Chem. 1996, 68, 729-733
Detection of Total Trans Fatty Acids Content in Margarine: An Intercomparison Study of GLC, GLC + TLC, FT-IR, and Optothermal Window (Open Photoacoustic Cell) Jan Paul Favier* and Dane Bicanic
Laser Photoacoustic Laboratory, Department of Agricultural Engineering and Physics, Wageningen Agricultural University, Bomenweg 4, NL 6703 HD Wageningen, The Netherlands Peter van de Bovenkamp
Department of Human Nutrition, Wageningen Agricultural University, Biotechnion, Bomenweg 2, 6703 HD Wageningen, The Netherlands Mihai Chirtoc
Institute for Isotopic and Molecular Technology, P.O. Box 700, 3400 Cluj-Napoca 5, Romania Per Helander
AB Varilab, Fullerstava¨ gen 32, Huddinge, Sweden
Four techniques, i.e., gas-liquid chromatography, gasliquid chromatography + thin-layer chromatography, and two spectroscopic methods, Fourier transform infrared spectroscopy and optothermal window, a variant of the open photoacoustic cell, were intercompared to determine their potential to detect the total trans fatty acid content in margarine. At the same time, this study represents a first application of the optothermal window technique at long wavelengths (10 µm). The total trans fatty acid data obtained by different methods show good mutual agreement. Besides offering several attractive advantages above conventional methods, the optothermal window also proved suitable for measuring total trans fatty acid content as low as 2%. Oils and fats are primary sources of lipids that provide a major portion of the energy supply in the human diet. The unsaturated constituents of most natural vegetable and marine oils contain only nonconjugated or isolated double bonds in cis configuration; a sizable fraction of these are converted to trans isomers during the process of hydrogenation needed to give fats and margarine a better consistency and stability.1 Since the importance of monounsaturated fatty acids in reducing saturated fat intake, thereby lowering the serum level * Address correspondence to this author. E-mail: Jan.PaulFavier@ user.aenf.wau.nl. (1) Osborne, B. G.; Fearn, T.; Hindle, P. H. Practical NIR Spectroscopy with Applications in Food and Beverage Analysis, 2nd ed.; Longman Scientific & Technical: Singapore, 1993. 0003-2700/96/0368-0729$12.00/0
© 1996 American Chemical Society
of the atherogenic low-density lipoprotein cholesterol, has been emphasized by various studies,2 the content of total trans fatty acids in edible oil is regarded as an important issue. It was shown that the effect of trans fatty acids (TFA) on the serum lipoprotein profile is at least as unfavorable as that of the cholesterol-raising saturated fatty acids. The TFA not only raise the low-density lipoprotein cholesterol level, but also lower the high-density lipoprotein cholesterol levels.2 The recommended reduction of saturated fatty acids might lead to increased consumption of TFA. Since the TFA are the best substitute for saturated fatty acids in a production process of semisolid and solid fats in the edible oil industry,2 the demand for the availability of a reliable and rapid on-line method capable of determining TFA is self-evident. At present, most commonly used methods to detect TFA in margarine utilize chromatography and infrared spectroscopy, each having its own specific pros and cons. In their infrared spectra, oils and fats feature several characteristic, absorbing bands with large absorption coefficients β (m-1); the one centered at 966 cm-1 is recommended and widely used for measurements of TFA.3 This in turn requires the use of a cell with short (
