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Composition of tomatoes and tomato products in antioxidants (WG1) page 41
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mg/kg fresh matter) resulted when plants were transferred from shade to sunshine at the time
the fruit was mature green.
For tomatoes grown in sand culture (cv. Bonny Best) Somers et al.(1951) found that
the ascorbic acid content of the fruits was associated with the degree to which they were
shaded inside the plants: vitamin C content increased significantly from 298 mg/kg fresh
matter in “full shade” fruit to 344 mg/kg fresh matter in “fully exposed” fruit. This was
confirmed by Murneek et al.(1954): greenhouse-grown tomatoes (cvs. Marglobe and
Stokesdale) were usually lower in vitamin C than those grown outdoors, due chiefly to lower
light intensity and shorter days during late fall, winter and early spring. There seemed to be a
seasonal increase in concentration in vitamin C in field-grown fruit from early summer to late
summer (250 to 350 mg/kg fresh fruit). There was a strong positive correlation between
vitamin C concentration and light intensity. In shade situation (by foliage) might reduce it by
15-20% compared to in light situation. The side of a tomato that was directly exposed to light
was invariably higher in vitamin C that the shaded side. Brown (1954) also reported that fruit
receiving direct sunlight were higher in ascorbic acid than fruits shaded by leaves or artificial
cover, showing that, like many previous studies, light is the predominant factor in ascorbic
acid production and accumulation in plant material. Venter (1977) demonstrated also that
vitamin C content of tomato fruit (cv. Sieger) increased (from 250 to 400 mg/kg fresh matter)
with the length of the radiation period, with differences between shaded or unshaded fruits on
the same plant or between shaded or unshaded fruit sections. López-Andréu et al.(1986) also
found lower fruit vitamin C values in greenhouse with less direct sunlight than for field
cultivated fruit. Another field study on the effects of shading with netting (0, 35, 51 or 63%
shade) conducted in Egypt on two tomato cultivars showed that ascorbic acid content
decreased with increasing shading while the best yield components were obtained from plants
grown under 35% shading (El-Gizawy et al, 1993). Adegoroye and Jolliffe (1987) found that
in tissues of fruit directly exposed to radiation (650 W m -2 from incandescent lamps inducing
visible injury), ascorbic acid content was decreased, although treated fruit exhibited some
capacity for ascorbic accumulation during subsequent storage. It has been suggested that
radiation injury in tomato fruit might be due to generalised effects of overheating in irradiated
tissues.
Light exposure seems to be favourable to vitamin C accumulation in the tomato fruit,
somewhat like for carotene synthesis in fruit. Thus fruit vitamin C and β-carotene contents
might be affected positively by not too close plant spacing to provide radiation and the use of