engleski

Optimization of the DSC method for determining the oxidative stability of virgin olive oil

The oxidative stability of fats and oils is a crucial parameter that determines the shelf life of a product, but also the general use of the fats and oils. Differential scanning calorimetry (DSC) is a promising new technique that is fast, reliable and uses the exothermic character of the oxidation reaction to determine the induction time (in the isothermal DSC method) or the induction temperature (in the non-isothermal, i.e., dynamic DSC method). The objective of the present study was to optimize the conditions of the DSC method to determine the oxidative stability of virgin olive oil. Both the isothermal and dynamic methods were developed on a 214 Polyma DSC (NETZSCH-Gerätebau GmbH) and optimized using extra virgin olive oil from the Croatian market. The parameters studied were sample size (4, 8 and 12 mg), sample preparation (use of an open or a sealed pan with a pinhole), temperature (130, 140 and 150 °C) for the isothermal method and heating rate (5, 10, 15 and 20 °C/min) for the dynamic method. The results show that the DSC method is a reliable method for determining oxidation stability for both isothermal and non-isothermal methods. Sample size did not affect induction time, but a smaller portion size resulted in better reproducibility of the results. Regarding sample preparation, there was no statistical difference between results obtained with an open or sealed aluminum pan. However, it is better to use a hermetically sealed pan with a pinhole to protect the instrument from possible contamination. The induction time at 130 °C was 287 minutes, which was considered unacceptable, while a temperature of 140 °C proved to be optimal. A temperature of 150 °C also showed satisfactory reproducibility of results, but a longer induction time at 140 °C makes it easier to track changes between different oils or during storage. For the determination of the induction temperature (dynamic DSC), a heating rate of 15 °C/min proved to be optimal. Although repeatable results were also obtained with a heating rate of 10 °C/min, the use of a higher temperature rate can significantly speed up the analysis. The other two heating rates were considered unsuitable due to the lack of reproducibility.

dynamic DSC, extra virgin olive oil, induction temperature, induction time, isothermal DSC, oxidative stability

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