Decolouration in virgin olive oil is so natural?
Chlorophyll pigment fraction was thermally more stable than carotenoid pigment fraction. Differences between the oily matrices did not affect the reaction mechanisms
Kinetic models are capable of predicting shelf life in keeping with the different variables that can affect the degradation of the food item. In this work, virgin olive oils (VOOs) extracted from olive fruits at three ripening stages with high, medium and low pigment content respectively, were thermodegraded to characterize the kinetic and thermodynamic parameters for the oxidation of two pigment fractions: a green fraction (chlorophylls) and a yellow fraction (carotenoids).
A first-order kinetic mechanism was appropriate for describing the decolouration processes under non-oxygen thermal auto-oxidation. A marked effect of temperature has been pointed out, with the carotenoids (CARs) being the most affected by heat. The kinetic constants for the CARs degradation were about 3.6 times higher than the respective for chlorophylls (CHLs) that showed a more stable structure to decolouration by heat. As well, higher activation energy of CHLs (16.03 ± 0.26 kcal · mol- 1) as compared to CARs (15.45 ± 0.17 kcal · mol- 1) implies that a smaller temperature change is needed to increase the kinetic constant of CHLs.
Neither isokinetic ratio and nor compensation existed between the three VOO matrixes and further, for each pigment fraction (CHLs or CARs) all kinetic constants were explained by a single Arrhenius line. Consequently, the differences between the oily matrices did not significantly affect the decolouration mechanisms, and moreover, the kinetic parameters obtained as temperature functions according to Arrhenius model, can be used to develop a prediction mathematical model for decolouration of CHL and CAR pigment fractions in VOO over time and depending on temperature.
Ramón Aparicio-Ruiza, Beatriz Gandul-Rojasb, Decolouration kinetics of chlorophylls and carotenoids in virgin olive oil by autoxidation, Food Research International, Available online 6 June 2014, ISSN 0963-9969