Determination of Total Polar Material in Frying Fat by Preparative
Column Chromatography and by Measurement of the Dielectric
Constant – A Comparative Interlaboratory Study
Heinz-Dieter Isengard, Georg Merkh, University of Hohenheim
Stuttgart, Germany
One of the criteria to assess the degree of degradation of frying fats is the mass
concentration of so-called total polar material in the fat.
Two official methods exist for determining this mass concentration, both based on a
preparative column chromatographic technique. They divide the fat in a polar and a
non-polar fraction. The results of these methods are available only after many hours,
usually only at least one day after taking the sample. The analyses need skilled
personnel and laboratory equipment as the use of hazardous chemicals is involved.
Both techniques include several analytical steps with possible errors which affect the
repeatability and the reproducibility of the methods. A distinction between different
compounds is not made. The specific polarity of the components is not important, they
just fall in one of the categories “polar” or “non-polar” according to the definition of the
method. Only the mass of the molecules is regarded. A heavy molecule with a low
polarity (but polar by definition) counts more than a light molecule with a high polarity.
An alternative method measures the dielectric constant of the fat which rises with
increasing contents of polar molecules. Results are obtained on-site and after a couple
of minutes. In the case of “negative” results, measures can be taken immediately. The
fat is analysed without separation by a probe. The decisive property of the components
is polarity and not mass. A molecule with a high polarity counts more than a less polar
molecule with the same mass. Even molecules with a very low polarity, which would fall
in the non-polar fraction in the chromatographic method, contribute to the measured
value. The results of the two techniques are rather close to each other in spite of the
principally different approaches.
The two techniques were compared to each other in an interlaboratory test. Differences
in the results were observed. The scattering of results obtained with the
chromatographic method was much higher than those received with the dielectric
technique which proved to be extremely repeatable and reproducible.