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Composition of tomatoes and tomato products in antioxidants (WG1) page 20
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well known for its antioxidant properties, also decreases during ripening, especially between
the immature green and mature green stages.
The maximum concentration of ascorbic acid is estimated in tomato fruits at yellow
turning stage (around 250 mg/kg fresh matter for numerous cultivars). This content decreases
during ripening. This decrease is certainly due to its antioxidant function when the ripening
cells absorb high amount of oxygen; this is the result of an increase in respiration,
characteristic of climacteric fruits (with an autocatylitic synthesis of ethylene) (Macheix et
al.1990).
Changes in tocopherols are different among α, β and γ forms. There is an increase in α
and β-tocopherol during ripening reaching 3 mg/kg fresh matter for α and 0.5 mg/kg fresh
matter for β isomer at the red stage; γ-tocopherol reaches a maximum at colour break stage,
between 1 and 1.5 mg/kg fresh matter. Its level declines in a similar manner than ascorbic
acid (Abushita et al.1997).
6. Influence of cultural practices and agronomic aspects on antioxidants content of
tomato fruit
6.1. Lycopene, β-carotene and total carotene
6.1.1. Introduction
The colour of red tomatoes is determined primarily by their lycopene content (Stevens
and Rick, 1986). Johjima and Matsuzoe (1995) have shown that the fruit colour values (a/b)
were highly correlated with lycopene content, including cis and trans forms. But according to
Koskitalo and Ormrod (1972) surface colour could not be used to specify accurately the
internal colour of fully ripened tomatoes. At lycopene concentrations between 32 and
43 mg/kg fresh matter, fruit colour turns from orange to red and satisfactory red coloration
required a total carotene concentration in excess of 55 mg/kg fresh matter of which lycopene
accounted for 90% of the carotenes. Giovanelli et al.(1999) measured the colour changes at
seven stages during vine and post-harvest ripening on two genotypes (Normal Red and