Thermal degradation kinetics of bixin in an aqueous model system

A. DE O. RIOS; C.D. BORSARELLI; A.Z. MERCADANTE

JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY

American Chemical Society

Lugar: Columbus, OH, 43210, USA; Año: 2005 vol. 53 p. 2307 - 2311

0021-8561

The kinetic of the thermal degradation of the natural cis carotenoid bixin in water/ethanol (8:2) solution was studied by high-performance liquid chromatography as a function of temperature (70 – 125 ºC). The bixin decay and products formation (e.g. di-cis and all-trans isomers, and a degradation compound C17) curves did not adjust well to a first-order rate law, but very good fittings were obtained using a bi-exponential 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 immediately formed (15 kcal/mol) together with the decay of bixin, followed by a slower consumption indicating their role as reaction intermediates. In fact, the di-cis isomers could easily return to bixin (Ea » 3 kcal/mol) or yield the primary degradation product C17 with an energy barrier of 6.5 kcal/mol. In turn, 24 kcal/mol was necessary for the Bix à all-trans step, explaining its slower formation.