Study of the time-course of cis/trans (Z/E) isomerization of lycopene, phytoene, and phytofluene from tomato.

In this study we investigated the formation of isomers of lycopene, phytoene, and phytofluene from tomato and their theoretical energy. The results indicated that certain (Z)-isomers are favored thermodynamically and/or kinetically over their (all-E)-counterparts. The relative percentages of (5Z)-lycopene in either thermodynamic or kinetic equilibria were approximately 33%, and those of (all-E)-lycopene were only approximately 22%. Most strikingly (15Z)-phytoene was the major isomer (>90%) when the thermodynamic or the kinetic equilibria were reached. These observations can explain the high levels of lycopene (Z)-isomers found in humans and their rapid formations upon additions of oil to tomato products. In addition, the results can be useful to predict the isomeric forms of lycopene, phytoene, and phytofluene expected in foods as well as in plasma and tissues upon ingestion. In light of the data in the present study, the use of certain geometrical isomers of phytoene, phytofluene and lycopene on their own or as mixtures is recommended in future studies aimed at assessing their possible bioactivity.