The Chemistry and Biology of Lycopene : Antioxidant for Human Health

Lycopene : Antioxidant

Abstract

More than 600 carotenoids are known to be naturally occurring. These predominantly colourful molecules, found in plants, fungi and bacteria undergoing photosynthesis, are widespread in vegetables and fruits. Carotenoids are divided into two main groups. Of them, the highly unsaturated hydrocarbons consisting of lycopene, α-, β-, and γ-carotene build the first group, whereas xanthophylls, such as β-cryptoxanthin, lutein and zeaxanthin are considered as the second big carotenoid group.

Lycopene, a representative of the hydrocarbon carotenoids with the molecular formula of C₄₀H₅₆, has an acyclic open-chain structure consisting of 13 double-bonds. Two of them are non-conjugated, whereas eleven are conjugated double bonds, thereby building a chromatophore. This distinctive conjugated polyene structure accounts for the ruby colour and the antioxidant properties of lycopene. It has a distinct lipophilic character, which makes it nearly insoluble in ethanol, methanol and water. Due to its acyclic structure and the absence of a β-ionone ring, there is no pro-vitamin A activity to be found in lycopene, which is the reason for its differing biochemistry, as compared to α- and β-carotene.

Due to its polyene-structure, providing an electron-rich system, lycopene is an eligible target for electrophilic reagents. Thus, it shows an extreme reactivity towards oxygen and free radicals. Lycopene is known to be the most potent oxygen quenching reagent among carotenoids, and furthermore, it provides the ability to intervene in reactions initiated by free radicals, like OH^−· or peroxy radicals. Its excellent anti-oxidant properties are most likely the basis for its preventive role towards cancer and other chronic diseases.

However, the lycopene concentration in fresh fruits and vegetables shows a great variability, depending on seasonal environmental conditions, geographic location, climatic situation, species and maturity which may be taken as indices for the best sowing season, place, species/varieties to be planted and date/time of harvest. The vegetables and fruits thus obtained would be rich in lycopene content, which in turn would have a major beneficial impact on human health.