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Processing and Bioavailability (WG2) page 41
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Other aspects
At this point, in order to provide a more detailed view various topics must be addressed
which are of importance for quality (ratio between lycopene content and colour of tomato
conserves) and for the tomato/health aspect, which is the specific aim of this CA.
1. Lycopene and colour
Various studies have been carried out on the relationship between chemical-physical and
sensory parameters of processed tomato, and several methods have been set up to evaluate the
quality of products. Despite this, data on the relationship between lycopene content and
sensory attributes, in particular colour, are poor, although this relationship may be useful to
select products and to set up rapid methods of measuring the lycopene content in raw and
processed tomatoes.
Since lycopene is responsible for the red colour of tomatoes (95% of the carotenoids in the
ripe fruit), it might seem natural, at first sight, to presume that a correlation exists between
lycopene content and the colour of the tomato and its products; colour is normally measured
by means of reflectance with tristimulus colorimeters (Gardner, Hunterlab, Minolta) which
provide measurements with three parameters: L (visual lightness), a (red colour) and b
(yellow colour) and combinations of these (a/b, L*b/a, (∆L 2 + ∆a 2 + ∆b 2 ) 1/2 with respect to a
reference value, etc). In effect, this does not occur (Koskitalo, Zanotti), the attempts made
yielding correlation coefficients lower than 70%. This is probably because the comparison
made is between an objective measurement (absolute lycopene content) and an "artificial"
instrumental one. Furthermore, an analytical measurement of lycopene yields the value of all
the lycopene present, and not that which is responsible for the colour of the tomato or tomato
product, on account of its physical state (solid coagula, of varying dimensions depending on
the degree of crushing, in a liquid matrix). Stated in simple terms, the same red colour may be
produced by a cumulus of small red granules, either empty or full of pigment.
The same problem occurs with tomato powders, in which the same powder reduced to a
different physical state (granulometry) yields, even to the naked eye, completely discordant
results, despite starting from the same product and hence the same lycopene content.