Formation of apocarotenals and epoxycarotenoids from β-carotene by chemical reactions and by autoxidation in model systems and processed foods

It is generally accepted that oxidation of carotenoids begins with epoxidation and cleavage to apocarotenals. However, systematic studies to demonstrate occurrence of these reactions are lacking. In this study, the products formed by epoxidation with m-chloroperbenzoic acid (MCPBA), oxidative cleavage with KMnO₄ and autoxidation in model systems, in the presence and absence of light, at ambient condition were identified. The presence of oxidation products was also verified in processed products. β-carotene-5,6-epoxide, β-carotene-5,8-epoxide, β-carotene-5,6,5′,6′-diepoxide, β-carotene-5,6,5′,8′-diepoxide and β-carotene 5,8,5′,8′-diepoxide were formed by the reaction of β-carotene with MCPBA. The oxidation products with KMnO₄ were identified as β-apo-8′-carotenal, β-apo-10′-carotenal, β-apo-12′-carotenal, β-apo-14′-carotenal and β-apo-15-carotenal, along with semi-β-carotenone and monohydroxy-β-carotene-5,8-epoxide. Except for β-carotene 5,6,5′,6′-diepoxide, these products were detected in the model systems. Some of these products were also found in mango juice, acerola juice and dried apricot. Increased Z-isomerization was also observed and Z-isomers of the oxidation products were detected.