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Identification and thermal degradation kinetics of chlorophyll pigments and ascorbic acid from ditax nectar (Detarium senegalense J.F. Gmel)

Diop Ndiaye N., Dhuique-Mayer C., Cisse M., Dornier M.. 2011. Journal of Agricultural and Food Chemistry, 59 (22) : p. 12018-12027.

DOI: 10.1021/jf203582k

Detarium senegalense J.F. Gmel (ditax) is a forest tree found in Senegal the fruits of which are characterized by an attractive green flesh with a high amount in ascorbic acid. It is generally consumed as a nectar in Senegal. In this study, the main pigments of ditax pulp were identified and quantified by HPLC-DAD. Pheophytin a (128 mg/kg), which represents 58% of the total pigments, followed by hydroxypheophytin a0 (33 mg/kg), chlorophyll b (24 mg/kg), and chlorophyll a (20 mg/kg) was the major pigment of ditax pulp. Lutein and ?-carotene were present in lower amounts (4.6 and 3.6 mg/kg, respectively). The thermal degradation kinetics of pheophytin a, hydroxypheophytin a0, and ascorbic acid were determined at temperatures ranging from 60 to 95 _C in ditax nectar. Pheophytin a was the most heat sensitive. Thermal processing induced the formation of degradation products such as pyropheophytin a and pyropheophytin b. The kinetics parameters have been calculated according to the models of Arrhenius, Eyring, and Ball. Following the Arrhenius relation, activation energies of pheophytin a, hydroxypheophytin a0, and ascorbic acid were, respectively, 79, 74, and 46 kJ mol_1. Losses calculated during isothermal treatments were close to experimental losses in pheophytin a, hydroxypheophytin a0, and ascorbic acid. The Eyring model can then be used to predict chlorophyll pigments and vitamin C losses during pasteurization of the nectar (<10%).

Mots-clés : caesalpinioideae; jus de fruits; pulpe de fruits; traitement thermique; chlorophylle; phéophytine; acide ascorbique; biodégradation; identification; réaction chimique; modèle de simulation; sénégal; detarium senegalense; cinétique

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