FTIR Spectroscopy and DFT Calculations to Probe the Kinetics of β-Carotene Thermal Degradation

The thermal degradation of β-carotene in air was investigated. The sample was heated at different temperatures (90, 100, 115 and 130 °C) for periods of up to 8 h to perform a complete kinetic study, the product analysis having been carried out via infrared spectroscopy in attenuated total reflectance mode coupled to DFT-calculations. The kinetics of this thermal degradation process was found to follow a first order scheme, with rate coefficients varying from k90 °C= (2.0 ± 0.3)x10-3 to k130 °C= (11.0 ± 0.7)x10-3 min-1, the experimental activation energy having been calcu-lated as (52 ± 1) kJ mol-1. This Ea value is close to the DFT energies corresponding to a C15-15´ or a C13-14 cis-trans isomerization, followed by the formation of a carotene-oxygen diradical, that was characterized for the first time. Comparison between the experimental and calculated infrared data confirmed the C15-15´-cis rupture as the predominant reaction pathway and retinal as the major degradation product.