There is some evidence that isomeric form may be an
important factor in the bioactivity of certain carotenoids. For instance,
cis-lycopene is found at high levels in human serum and
tissues, while in most plant tissues and foods, the all-trans form
predominates (Boileau et al., 1999). Unlike lycopene, the trans
isomer of lutein is the predominant formfound both in raw plant
materials and some human tissues, and has also been found to be
preferentially absorbed by cell cultures (Chitchumroonchokchai
et al., 2004).
The finding that cis-lycopene isomers concentrations are
higher in animal tissues than in raw plant materials has created
debate within the nutrition community as to whether cis