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Thermal degradation of antioxidant micronutrients in Citrus juice : Kinetics and newly formed compounds

Dhuique-Mayer C., Tbatou M., Carail M., Caris-Veyrat C., Dornier M., Amiot M.J.. 2007. Journal of Agricultural and Food Chemistry, 55 : p. 4209-4216.

DOI: 10.1021/jf0700529

The thermal degradation kinetics of vitamin C, two carotenoids ([bêta]-carotene and [bêta]-cryptoxanthin), and hesperidin, as a function of temperature, were determined for Citrus juice [Citrus sinensis (L.) Osbeck and Citrus clementine Hort. ex Tan]. The influence of dissolved oxygen on the rate of ascorbic acid degradation was also assessed. Analysis of kinetic data suggested a first-order reaction for the degradation of vitamin C and carotenoids. The kinetics parameters Do, z, and Ea have been calculated. Following the Arrhenius relationship, the activation energy of ascorbic acid was 35.9 kJ mol-1 and agreed with the range of literature reported value. The results on vitamin C and carotenoids from citrus juice made it possible to validate the predicting model. Thermal degradation of carotenoids revealed differences in stability among the main provitamin A carotenoids and between these and other carotenoids belonging to the xanthophyll family. The activation energies for the two provitamin A carotenoids were 110 and 156 kJ mol-1 for [bêta]-carotene and [bêta]-cryptoxanthin, respectively. On the other hand, no degradation of hesperidin was observed during thermal treatment. Finally, the vitamin C in citrus juice was not as heat sensitive as expected and the main provitamin A carotenoids present in citrus juice displayed a relative heat stability. The high-performance liquid chromatography-diode array detection-mass spectrometry analysis of degradation products showed that the isomerization of the epoxide function in position 5,6 into a furanoxide function in position 5,8 was a common reaction for several xanthophylls. These findings will help determine optimal processing conditions for minimizing the degradation of important quality factors such as vitamin C and carotenoid in citrus juice.

Mots-clés : jus de fruits; agrume; citrus; acide ascorbique; caroténoïde; hplc; dégradation; cryptoxanthine; bêta-carotène

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