Rios Alessandro de O, Borsarelli Claudio D, Mercadante Adriana Z
Departamento de Ciência de Alimentos, Faculdade de Engenharia de Alimentos, UNICAMP, Cx. Postal 6121, 13083-970, Campinas, SP, Brazil.
J Agric Food Chem. 2005 Mar 23;53(6):2307-11. doi: 10.1021/jf0481655.
The kinetics of the thermal degradation of the natural cis carotenoid bixin in a water/ethanol (8:2) solution was studied as a function of temperature (70-125 degrees C), using high-performance liquid chromatography. The curves for the decay of bixin and formation of products (e.g., di-cis and all-trans isomers and a C17 degradation compound) did not adjust well to a first-order rate law, but very good fits were obtained using a biexponential model. This mathematical modeling gave the rate constant values for the formation of the primary products from bixin, and the energy barrier for each step was obtained. The di-cis isomers were formed immediately (15 kcal/mol) together with the decay of bixin, followed by a slow consumption, indicating their role as reaction intermediates. In fact, the di-cis isomers could easily revert to bixin (Ea approximately 3 kcal/mol) or yield the primary C17 degradation product, with an energy barrier of 6.5 kcal/mol. In turn, 24 kcal/mol was necessary for the Bix --> all-trans step, explaining its slower formation.
使用高效液相色谱法，研究了天然顺式类胡萝卜素胭脂树橙在水/乙醇（8:2）溶液中的热降解动力学与温度（70 - 125℃）的关系。胭脂树橙的衰减曲线和产物（如双顺式和全反式异构体以及一种C17降解化合物）的形成曲线并不完全符合一级速率定律，但使用双指数模型得到了很好的拟合。这种数学建模给出了从胭脂树橙形成初级产物的速率常数，并且得到了每一步的能垒。双顺式异构体与胭脂树橙的衰减同时立即形成（15千卡/摩尔），随后缓慢消耗，表明它们作为反应中间体的作用。事实上，双顺式异构体可以很容易地转化回胭脂树橙（活化能约为3千卡/摩尔）或生成初级C17降解产物，其能垒为6.5千卡/摩尔。反过来，从胭脂树橙转化为全反式异构体需要24千卡/摩尔，这解释了其形成较慢的原因。
