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An ID for each oil, to defend origin and genuineness

Starting with the study of oil behavior under thermal variations, all the necessary knowledge on “differential calorimetry”: an important technique to verify the different behavior of different oil. The purpose? To identify possible frauds

I first approached differential calorimetry about 25 years ago, when I was studying fats which could compose a good cream spread like Nutella. That was the time of innovation at Carapelli and each day new ideas were proposed, which were totally or in part carried on with satisfaction and creativeness.

Solid fats like palm or coconut oil, or cocoa butter, other being analyzed through classical analytical techniques, were normally subject to the study of their response to melting and freezing, in order to derive a DSC (Differential Scanning Calorimetry) curve.

According to this technique, oil, which is constituted of triglycerides, composed by saturated, monounsaturated and polyunsaturated fatty acids, is brought to high temperatures (50°C) and subsequently to low temperatures (- 40°C), thus observing the liquid to solid and solid to liquid transitions.
In the last decade, as I was studying with particular attention virgin olive oils, I had the idea of using this technique to verify the different behaviors of different vegetal oils, obviously with the idea of identifying potential fraudulent mixtures.

I have always been very curious to oil responses to thermal changes, especially because consumers often wonder why a certain oil easily freezes, while another remains limpid at cellar temperatures, and given that the different behaviors are related to genuineness. I always explained that it is normal for an oil to freeze, forming crystals which will later melt and contribute to bring the temperature back to 20°C, although there is a certain variability in behaviors, definitely related to the compositions in terms of triglycerides and to the presence of wax in the case of unfiltered oils.

For this long series of reasons, the study of seed and olive oils by means of the DSC technique looked very promising and Carapelli started a collaboration with CNR in Pisa (Dr. Salvetti, Dr. Angiuli and Dr. Tombari) in 2004. to submit extra virgin oils of different origin, refined and deodorated oils, seed oils like sunflower oil for analysis.

To tell the truth, the idea of identifying an oil through a sort of finger print or ID was exciting and the easiness of the technique, as well as the minimum quantity of oil required to carry out the analysis represented an immediate advantage.

In figure 1, the freezing and melting curve is reported. the sample is heated up to 50°C, maintained at this temperature for 3 minutes, then cooled to - 40°C at a rate of 10°C/minute, kept at - 40°C for six minutes, then heated up to 50°C again.

No change is noted during heating in different preservation conditions (light and darkness), which put in evidence different profiles of the high and low temperature peaks.

In figure 6 a different analysis, carried out on various mixtures of extra virgin and refined oils, is shown. The P1 peak is high in refined oils, while P3 is high in extra virgin olive oils.

Last, figure 7 emphasizes the differences between mixtures of seed and extra virgin oils, and figure 8 between an extra virgin and a deodorated oil.
These examples show the behavior in the melting curve of different oils, the effect of preservation conditions, and the effect of mixing olive and seed oil.
Obviously each oil has its own peculiar profile, even though differences are not so macroscopic at times. The use of the DSC technique appears interesting mostly because it enables to determine the identity of two samples. For a producer, this is a fast test which can verify the correspondence between and informative sample and the sample of an extra virgin olive oil.

The hope to find a reliable method to solve problems such as origin and genuineness is high, but just like any other analytical method, an ample statistics of representative data is necessary to validate the scientific relevance of this method.

For now, my opinion is that we can state that this is a relatively new method in the application to vegetal oils (seeds and olive) and a promising one too. In the future, it may provide with interesting information; but we must not commit the mistake of thinking that this can be the panacea to all our problems.

Bibliografy

1. Dyszel, S.M. A rapid screening technique for vegetable oil identity by sub-ambient DSC. Thermochimica Acta, 1982, 57, 209-221

2. Dyszel, S.M.; Baish, S.K. Characterization of tropical oils by DSC. Thermochimica Acta, 1992, 212, 39-49.

3. Kaisersberger, E. Application of heat-flux DSC for the characterization of edible fats and oils. Anal. Proc. 1990, 27, 64-65.

4. Cebula, D.J.; Smith, K.W. Differential scanning calorimetry of confectionery fats – pure triglycerides – effects of cooling and heating rate variation. J. Am. 0il Chem. Soc. 1991, 68, 591-595

5. Adhvaryu, A.; Erhau, S.Z.; Perez, J.M. Wax appearance temperature of vegetable oils determined by differential scanning calorimetry: effect of triacylglycerol structure and its modification. Thermochimica Acta 2003, 395, 191-200.

6. Angiuli, M.; Ferrari, C.; Lepori, L.; Matteoli, E.; Salvetti, G.; Tombari, E.; Banti, A.; Minnaja, N. On testing quality and traceability of virgin olive oil by calorimetry. J. Therm. Anal. and Calorimetry 2006 (In press)

7. Sato, K. Crystallization behaviour of fats and lipids – a review. Chem. Eng. Sci. 2001, 56, 2255-2265.

8. Che Man, Y.B; Tan, C.P. Comparative Differential Scanning Calorimetry Analisis of Vegetable Oils: Effects of cooling rate variation. Phitochemical Analysis 2002, 13, 142-151.

9. Tan, C.P.; Che Man, Y.B. Comparative Differential Scanning Calorimetry Analisis of Vegetable Oils: Effects of heating rate variation. Phitochemical Analysis 2002, 13, 129-141.

10. Tombari, E.; Angiuli, M.; Ferrari, C.; Rigetti, M.C.; Salvetti, G.; Mattei, A.; Lorenzini, O. Adulterazioni dell’olio d’oliva extra vergine per aggiunta di olio di semi rilevabili con calorimetria DSC. Atti del convegno CISETA (Italy), 2005.

11. Kalnin, D.;Lesieur, P.; Artzner, F.; Keller, G.; Ollivon, M. Systematic investigation of lard polymorphism using combined DSC and time-resolved synchrotron X-ray diffraction. Eur. J. Lipid Sci. Technol. 2005, 107, 594-606.

12. Kalnin, D.; Garnaud, G.;, F.; Amenitsch, H.; Ollivon, M. Monitoring fat crystallization in aerated food emulsions by combined DSC and time-resolved synchrotron X-ray diffraction. Food Res. Intern.2002, 35, 927-934.

by Alissa Mattei
04 july 2011, Technical Area > Olive & Oil

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