Dear Abdul-Hammed,

This is actually a fairly simple, and for carotenoids reliable, quantification; although for tomatoe lycopene is really prevalent usually, and this decreases a bit the accuracy.

The general principle is that , as the compounds have different absorbance spectra, they have different absorbtivities for 2 judisciously chosen wavelengths. You build from this 2 equations (for optical densities at the 2 wavelengths) with 2 unknown values. This is general and will apply whenever you want to quantify 2 absorbing compounds, given that they give spectra of comparable intensities (if for example for one of them the OD is one, and for the other 0.01, it will not work well, errors in measurement become too much for reliable quantification of the minor compound) but different shapes (not too close either) in your concentration ranges. For carotenoiids the judisciously chosen wavelengths correspond to absorption peaks at 503 nm(one of the maxiima of lycopene) and 450 nom (for b-carotene). :

(Conc Lyc x Abs Lyc 503 nm) + (Conc Car x Abs Car 503 nm) = OD 503

(Conc Lyc x Abs Lyc 5450 nm) + (Conc Car x Abs Car 450 nm) = OD 450

The absorbtivities you may determine yourself using standards, or, as the standards for carotenoids are often of low purity, use reference values.

The actual references for that are quite old, but there was just recently a quite good article for these procedures in Postharvest Biology and Technology 66 (2012) 16–22.

Dear atherine Renard.

Thank you formyour response. We have designed such method in our laboratory and some are contesting the results. The referenced article has corroborated our own findings too. Thank you once again.

I leave a late contribution, but if you keep on working on tomato carotenoids, I would like to suggest a publication which I have coauthored some years ago, focusing on plum and cherry tomatoes. Regards.

[Muratore G., Licciardello F., Maccarone E. (2005). Evaluation of the chemical quality of a new type of small-sized tomato cultivar, the plum tomato (Lycopersicon lycopersicum). Italian Journal of Food Science, 17 (1), 75-81]

Dear Fabio,

Thank you for your response, however late it could be.

Your method involve the use of HPLC which separates carotenoids into fraction before determining their respective concentrations.

But the question asked was with respect to simultaneous determination of bet-carotene and lycopene concentration in heir mixture.

We were also charged with the assignment in our lab here and we did all we could and submitted the final report for publication. The report was submitted before the response of Catherine Renard making reference to:

Fish WW (2012). Postharvest Biology and Technology 66 (2012) 16–22.

Ours was also submitted before having the knowledge from Catherine and our own contribution was also accepted in September 2012 having submitted in February, 2012. Our own contribution, however too simple it is was published as:

Abdul-Hammed et al (2013). Simultaneous spectrophotometric determination of lycopene and beta-carotene concentrations in carotenoid mixtures of the extract of tomatoes, papaya and orange juice. Pakistan Journal of Scientific and Industrial Research, Ser. B: Biol. Sci. 56(2): 90-97.

Thank you once again.