KINETIC-MODEL FOR STUDYING THE ISOMERIZATION OF ALPHA-CAROTENE AND BETA-CAROTENE DURING HEATING AND ILLUMINATION

The thermoisomerization and iodine-catalyzed photoisomerization of all-trans-alpha- and all-trans-beta-carotene were kinetically studied using regression models. Carotene samples were heated at varied temperatures or exposed to a 20 W light for varied lengths of time. Isomerization and degradation reactions were monitored using HPLC with diode array detection. Four cis isomers of beta-carotene and three cis isomers of alpha-carotene were separated and detected. The degradations of both carotenes under heating at 150 degrees C or iodine/light treatment may fit the reversible first-order model. 9-cis and 13-cis were the major beta-carotene isomers formed during heating, while 13,15-di-cis was favored during iodine-catalyzed photoisomerization. The formation of 9-cis and 13-cis from all-trans-alpha-carotene was dependent upon the extent of heat or iodine/light treatment, and the latter was formed in greater amount under either treatment.