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Composition of tomatoes and tomato products in antioxidants (WG1) page 61
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7.1.2.6 Influence of the environment on physico-chemical properties.
The chemical and physical properties of lycopene and carotenoids in general are
strongly influenced by other molecules within the microenvironment, particularly associated
proteins and membrane lipids.
These interactions usually improve stability of lycopene, which is then less susceptible
to degradative oxidations. Indeed lycopene appears to be relatively stable during food
processing and cooking (Tonucci et al. 1995); the food matrix might protect lycopene. Also
lycopene appears to be relatively stable in blood samples collected using standard clinical
techniques and stored at –70°C over several years (Comstock et al. 1995).
7.1.3 Lycopene cis isomers.
7.1.3.1 Structures
Lycopene contains 13 carbon-carbon double bonds, among which 11 are conjugated.
The most thermodynamically stable form of lycopene is the all-trans (or all-E) form where all
the double bonds are in E configuration. With very few exceptions, lycopene from natural
plant sources exist predominantly in the all-trans configuration.
Theoretically, each one of the 11 carbon-carbon conjugated double bonds can undergo
isomerization to produce an array of mono- or poly-cis isomers of lycopene, all together
2 11 =2048 isomers are theoretically possible. Practically, because of steric hindrance, only
certain ethylenic groups can participate in cis-trans isomerization. In fact, about 72 lycopene
cis isomers are structurally favourable and only some have been observed (figure 8).