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

- The degradation of carotenoids was best described by a first-order kinetic model.
- The relationship of degradation rate for cis-carotenoids was obtained.
- A possible degradation mechanism of four all-trans-carotenoids was identified.

Thermal degradation kinetics of lutein, zeaxanthin, β-cryptoxanthin, β-carotene was studied at 25, 35, and 45 °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, β-cryptoxanthin, and β-carotene were described by a first-order kinetic model, with the order of rate constants as kβ-carotene > kβ-cryptoxanthin > klutein > kzeaxanthin. Activation energies of zeaxanthin, lutein, β-cryptoxanthin, and β-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.