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Kinetics of Chlorophyll Degradation and Color Loss in Heated Broccoli Juice

1999; American Chemical Society; Volume: 47; Issue: 6 Linguagem: Inglês

10.1021/jf980663o

1520-5118

C. Weemaes, V. Ooms, Ann Van Loey, Marc Hendrickx,

Free Radicals and Antioxidants

Degradation of chlorophyll in broccoli juice occurred at temperatures exceeding 60 °C. Chemical analysis revealed that degradation of chlorophyll a and b to pheophytin a and b, respectively, followed first-order kinetics and that chlorophyll a was more heat sensitive than chlorophyll b. Temperature dependencies of chlorophyll a and b degradation rate constants could be described by Arrhenius equations with activation energies (Ea) of 71.04 ± 4.89 and 67.11 ± 6.82 kJ/mol, respectively. Objective greenness measurements, using the −a value as the physical property, together with a fractional conversion kinetic analysis, indicated that green color degradation followed a two-step process. Kinetic parameters for the first degradation step were in accordance with the kinetic parameters for pheophytinization of the total chlorophyll content, as determined by chemical analysis (Ea ≈ 69 kJ/mol). The second degradation step, that is, the subsequent decomposition of pheophytins, was characterized by an activation energy of 105.49 ± 4.74 kJ/mol. Keywords: Chlorophyll; pheophytin; green color; broccoli (Brassica oleracea L. Italica); thermal degradation