Thermal degradation kinetics of bixin in an aqueous model system.
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.
Rios
Alessandro de O
Ade O
Departamento de Ciência de Alimentos, Faculdade de Engenharia de Alimentos, UNICAMP, Cx. Postal 6121, 13083-970, Campinas, SP, Brazil.
Borsarelli
Claudio D
CD
Mercadante
Adriana Z
AZ
D002338:Carotenoids / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D006358:Hot Temperature; D007700:Kinetics; D008433:Mathematics; D008956:Models, Chemical; D013053:Spectrophotometry; D013816:Thermodynamics; D014867:Water
D014867:Water; D002338:Carotenoids; C004588:bixin