Formation of volatile compounds from lycopene by autoxidation in a model system simulating dehydrated foods

Carotenoids are highly unsaturated natural pigments susceptible to oxidation during food processing and storage. Despite the recognized consequences of the oxidative degradation of carotenoids, the mechanisms involved are not well elucidated. In this work, a scheme for the study of volatiles produced by oxidative degradation of carotenoids in a model system simulating dehydrated foods was developed. Solid phase microextraction (SPME) was used for capturing the volatile compounds, which were identified by gas chromatography/mass spectrometry (GC/MS) and by comparison of Kovats indices. The scheme was applied to synthetic lycopene or lycopene isolated from watermelon. Ten volatile compounds were identified as products of the oxidative degradation of lycopene, the main volatiles formed being 6-methyl-5-hepten-2-one, citral or geranial (trans-3,7-dimethyl-2,6-octadienal) and neral (cis-3,7-dimethyl-2,6-octadienal). These compounds are often reported as volatiles of food sources of lycopene, but because lycopene was isolated in the present study, direct evidence for a precursor-product relationship is provided. Moreover, comparison of the volatile compounds generated in this study with those identified as products of enzymatic oxidation of lycopene indicates that enzymatic and non-enzymatic oxidation of lycopene may follow the same routes.