Cooking (Frying) oil quality management with measurement of the total polar material (TPM) – a comparison of chemical standard methods with a very rapid physical technique

Publication Type

Lecture

Authors

Isengard, H.-D., Zainal, Merkh, G.

Year of publication

2014

Conference name

Creative Food Science for the Future, Annual Meeting of the Korean Society of Food Science and Technology

Conference location

Gwangju, Korea

Conference date

25.-27.08.2014

Abstract

Cooking (frying) oil quality management with measurement of the total polar material (TPM) – a comparison of chemical standard methods with a very rapid physical technique

 

Heinz-Dieter Isengard¹, Zainal^1,2 and Georg Merkh¹

¹ University of Hohenheim, Institute of Food Science and Biotechnology,

70593 Stuttgart, Germany

² Hasanuddin University, Agricultural Faculty, Department of Agricultural Technology, Makassar 90245, Indonesia

 

One of the criteria to assess the degree of degradation of frying fats is the mass concentration of free fatty acids formed or, in general, the mass concentration of so-called total polar material (TPM). Two official methods exist for determining TPM, both based on a preparative column chromatographic technique. They divide the fat in a polar and a non-polar fraction. The results 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. A distinction between different compounds is not made. The specific polarity of the components is not regarded. They just fall in one of the categories “polar” or “non-polar” according to the definition of the method. 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 number (as well as the temperature on which it is dependent) of the fat which rises with increasing content 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 and on the spot to avoid the use of “exhausted” fats). 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 different techniques are rather close to each other in spite of the principally different approaches. This is shown for various frying fats and for different fried goods.

The two techniques were also compared to each other in an inter-laboratory test. Slight differences in the results were observed. The scattering of results obtained with the official method was much higher than that of the results received with the dielectric technique which proved to be extremely repeatable and reproducible.

It is therefore suggested to accept or introduce the probe technique as official method.