Weemaes C A, Ooms V, Van Loey A M, Hendrickx M E
Department of Food and Microbial Technology, Katholieke Universiteit Leuven, Belgium.
J Agric Food Chem. 1999 Jun;47(6):2404-9. doi: 10.1021/jf980663o.
Degradation of chlorophyll in broccoli juice occurred at temperatures exceeding 60 degrees 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 (E(a)) 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 (E(a) approximately 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.
西兰花汁中的叶绿素在温度超过60摄氏度时会发生降解。化学分析表明，叶绿素a和b分别降解为脱镁叶绿素a和b，遵循一级动力学，且叶绿素a比叶绿素b对热更敏感。叶绿素a和b降解速率常数的温度依赖性可用阿伦尼乌斯方程描述，其活化能（E(a)）分别为71.04±4.89和67.11±6.82 kJ/mol。以-a值作为物理性质的客观绿色度测量，结合分数转化率动力学分析表明，绿色降解遵循两步过程。第一步降解的动力学参数与化学分析测定的总叶绿素含量脱镁叶绿酸化的动力学参数一致（E(a)约为69 kJ/mol）。第二步降解，即脱镁叶绿素的后续分解，其活化能为105.49±4.74 kJ/mol。
