Lycopene Epoxides and Apo-Lycopenals Formed by Chemical Reactions and Autoxidation in Model Systems and Processed Foods

To gain a better understanding of the reactions and the underlying mechanisms of the oxidative degradation of lycopene, the products formed by epoxidation with m-chloroperbenzoic acid (MCPBA), oxidative cleavage with KMnO4, and autoxidation in low-moisture and aqueous model systems, under light exposure, at ambient temperature were identified. The presence of oxidation products was also verified in processed products (tomato juice, tomato paste, tomato puree, guava juice, goiabada). A total of 8 lycopene epoxides and a cyclolycopene diol were formed by the reaction of lycopene with MCPBA and 6 apo-lycopenals were produced with KMnO4. Some of these oxidation products were not detected in the model systems and in the foods analyzed, but the acid-catalyzed rearrangement product 2,6-cyclolycopene-1,5-diol and apo-12'-lycopenal were found in all model and food systems and lycopene-1,2-epoxide and 2,6-cyclolycopene-1,5-epoxide were found in the model systems and in all but 1 (goiabada) of the 5 foods analyzed. Other epoxides and apo-lycopenals were found in some systems. The inability to detect an intermediate product could be due to a fast turn over. Increased Z-isomerization was also observed and Z-isomers of the oxidation products were detected.