The hitherto scarcely investigated retro -carotenoid rhodoxanthin possesses high potential for coloration in the food and beverage industry using technofunctional formulations prepared thereof. Hence, we studied ( E/Z )-isomerization pathways of rhodoxanthin, including seven ( E/Z )-isomers comprising ( Z )-configured double bonds at unusual exocyclic and inner polyene chain positions. A mathematical approach was developed to deduce kinetic and thermodynamic parameters of six parallel equilibrium reactions interconnecting (all- E )-rhodoxanthin with mono-, di-, and tri-( Z )-isomers using multiresponse modeling. At 40–70 °C in ethyl acetate, reaction rate constants regarding the rotation from (all- E )- to (6 Z )-rhodoxanthin were 11–14 times higher than those of the common ( E/Z )-isomerization reaction at C-13,14 of the non- retro -structured carotenoid canthaxanthin. Moreover, the equilibrium reaction between (all- E )- and (6 Z )-rhodoxanthin was strongly product favored as indicated by negative Gibbs energies (−1.6 to −2.2 kJ mol –1 ), which is unusual for carotenoids within the studied temperatures. Overall, this study provides novel insights into structure-related dependencies of ( E/Z )-isomerization reaction kinetics and thermodynamics of polyenes.
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Schex et al. (2020) studied this question.