cantly increased incorporation of total and soluble solids and larger sugar
to acid ratios in a three-year field trial. This increase, however, was cor-
related with a decrease in red fruit yield and average fruit weight (Mar-
tineau et al., 1995).
Genetic Engineering: Designed Food for Health?
A key biochemical pathway in plants is the carotenoid pathway lead-
ing to the formation of two subclasses of compounds, the carotenes and
xanthophylls. A side chain of this pathway leads to the formation of
cytokinin catalyzed by isopentenyl transferase as mentioned above.
Carotenoids provide the color pigments in a variety of fruit and vegeta-
bles such as tomatoes, parsley, oranges, pink grapefruit, spinach and red
palm oil. In tomato, e.g., the red fruit color is provided by lycopene. Of
the more than 600 naturally occurring carotenoids, only the carotene
members -, - and ε-carotene possess vitamin A activity. These
carotenes, along with -carotene and the carotenes lycopene and lutein,
which do not convert to vitamin A, seem to offer protection against col-
orectal, breast, uterine and prostate cancers. Carotenes have also been
related to immune response and protection of the skin against ultravio-
let radiation. Additionally, they give antioxidative protection to the glu-
tathionine Phase II detoxification enzymes in the liver and thus support
elimination of pollutants and toxins from the body. The second
carotenoid subclass, i.e., the xanthophylls also comprise compounds of
positive biological effects such as canthaxanthin (UV protection), cryp-
toxanthin, zeaxanthin or astaxanthin. These compounds seem to exhibit
antioxidative protection of vitamin A, vitamin E and other carotenoids.
Like carotenes, the xanthophylls appear to be effective in a tissue-
specific way, e.g., cryptoxanthin is ascribed a protective effect in vagi-
nal, uterine and cervical tissues.
Carotenoids constitute an example of the growing number of plant
constituents for which positive health effects are postulated. In relation
to their effects or their origin, these constituents have been named
“nutraceuticals,” “phytochemicals,” “phytonutrients,” “phytofoods” or
“functional foods.” The definition of functional foods is still evolving.
Typically it refers to foods that, by virtue of physiologically active com-
ponents, combine a product’s nutritional benefits with a therapeutic or
health value. Such foods may be available in their natural state or may
be modified, processed or genetically engineered (Anon., 1995). Despite
uncertainties related to patenting, marketing and regulatory issues, nu-