Thermal degradation kinetics of all-trans and cis-carotenoids in a light-induced model system

Thermal degradation kinetics of lutein, zeaxanthin, beta-cryptoxanthin, beta-carotene was studied at 25, 35, and 45 degrees C in a model system. Qualitative and quantitative analyses of all-trans-and cis-carotenoids were conducted using HPLC-DAD-MS technologies. Kinetic and thermodynamic parameters were calculated by non-linear regression. A total of 29 geometrical isomers and four oxidation products were detected, including all-trans-, keto compounds, mono-cis-and di-cis-isomers. Degradations of all-trans-lutein, zeaxanthin, beta-cryptoxanthin, and beta-carotene were described by a first-order kinetic model, with the order of rate constants as k(beta-carotene) > k(beta-cryptoxanthin) > k(lutein) > k(zeaxanthin). Activation energies of zeaxanthin, lutein, beta-cryptoxanthin, and beta-carotene were 65.6, 38.9, 33.9, and 8.6 kJ/moL, respectively. cis-carotenoids also followed with the first-order kinetic model, but they did not show a defined sequence of degradation rate constants and activation energies at different temperatures. A possible degradation pathway of four carotenoids was identified to better understand the mechanism of carotenoid degradation. (C) 2017 Elsevier Ltd. All rights reserved.