Thermal degradation kinetics of carotenoids in a cashew apple juice model and its impact on the system color.

The thermal degradation kinetics of the main carotenoids of cashew apple in a juice model system was studied by HPLC and related to the changes of its CIELAB color parameters. Similar isomerization equilibrium constants and activation energies were observed for both all-trans-beta-carotene and all-trans-beta-cryptoxanthin. The curves for the decay of the main carotenoids and color changes showed a biphasic behavior that was best fitted by a biexponential equation. For the same heating conditions (60 or 90 degrees C), similar rate constants for the fast (gamma(1)) and slow (gamma(2)) decays were obtained for both the chemical (carotenoids) and physical (color) parameters monitored in the present research. This fact indicates that color parameters, such as DeltaE*, are good predictors of both all-trans-beta-cryptoxanthin and all-trans-beta-carotene thermal degradation. A mechanism for thermal carotenoid degradation was proposed, involving parallel irreversible and reversible coupled reactions of both the initial all-trans-beta-cryptoxanthin and all-trans-beta-carotene to yield, respectively, degradation compounds and mono-cis isomers.