ROLE OF TOMATO PROCESSING AND LYCOPENE ISOMERIZATION IN THE PREVENTION OF CHRONIC DISEASES

Submitted to: Ontario Tomato Resdearch Institute
BY
A. V. Rao
Department of Nutritional Sciences
Faculty of Medicine
University of Toronto
December 15, 2000

Lycopene, one of the most potent carotenoid antioxidant that is found predominantly in tomatoes and processed tomato products has been the subject of much research since epidemiological studies showed inverse association between tomato intake or blood lycopene level and the risk of cancer and other chronic diseases. Previous work in our laboratory has shown that blood and tissue levels of lycopene in prostate cancer patients to be significantly lower than their age matched controls. Results from a single dose lycopene administration suggest an impairment in the absorption of ;lycopene in prostate cancer patients compared to the healthy control subjects. It was speculated that Cancer patients perhaps lack the ability to isomerize the all-trans lycopene to its cis-isomers which have been shown previously to be absorbed more efficiently.

A study was undertaken with the financial assistance from the Ontario Tomato Research Institute (OTRI) with the overall objective of studying lycopene isomerization and its biological significance.

Specific objectives were to (a) Estimate cis-isomeric contents of lycopene in different tomato products. (b) Study the effect of temperature and the presence of lipids on cis-isomerization of lycopene. (c) Estimate the levels of serum total, trans and cis-isomeric forms of lycopene in animals and healthy human subjects.

Results from our study have indicated the following conclusions:

1. Raw tomatoes contain predominantly all-trans lycopene (93.1% all trans and 6.9% cis- lycopene)

2. Isomeric forms of lycopene in tomato lycopene oleoresin is similar to raw tomatoes (95.4% all trans and 4.6% cis-lycopene)

3. Processed tomato products contain significantly higher levels of cis-lycopene compared to raw tomatoes (tomato juice - 33% higher, tomato ketchup - 84% higher and tomato soup 143% higher cis-lycopene)

4. Presence of oil further enhance the levels of cis-lycopene in tomato juice. Olive oil being the most efficient compared to corn oil and butter (9.12%, 16.18%, 23.26% and 15.47% cis-lycpene in tomato juice and tomato juice with corn oil,, olive oil and butter respectively)

5. Administration of all trans lycopene to rats results in enrichment of cis-lycopene in the serum and tissues (All trans to cis-lycopene ratios in the oleoresin, lungs, heart, spleen, liver, prostate and serum are 11.91, 0.33, 1.61, 0.77, 0.48 and 0.59 respectively)

6. Ingesting all trans lycopene by healthy human subject in the form of tomato juice, tomato sauce and oleoresin for one week resulted in enrichment of cis-lycopene in the serum.

These results clearly indicate isomerization of lycopene to its cis-isomers by heat in in vitro system and by bioctalysts (lycopene isomerases?) under in vivo conditions. The biological significance of such isomerization is not clear at this time. Computer modeling of lycopene isomers has shown 5-cis lycopene to be the most stable and having the highest antioxidant potential (manuscript submitted to the Journal of Free Radical Biology and Medicine, September 2000). It is also not clear as to where in the body lycopene is isomerized to its cis-confugeration. Is it at the level of the gut or post absorption at the level of liver and other tissues? Further research is needed to clarify these questions and to understand the biological significance of lycopene isomerizatiopn in human health.