Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

Chapter 13
Isoprenoid Biosynthesis in
Fruits and Vegetables
Andrew Schofield, H.P. Vasantha Rupasinghe, and Gopinadhan Paliyath
13.1 Isoprenoids in plants
The isoprenoid pathway provides the largest class of secondary metabolic products (over
25,000) found in higher plants, and include fragrance components (monoterpenes such
as geraniol, nerol, and citronellol), sterols (sitosterol, stigmasterol, etc.), carotenoids
(lycopene, xanthophylls), tocopherols, hormones (gibberellins, abscisic acid, brassinosteroids,
certain cytokinins), phytyl side chain of chlorophyll, phylloquinone, plastoquinone,
ubiquinone, and phytoalexins (Bach, 1995; Chappell, 1995; McGarvey and Croteau, 1995;
Eisenreich et al., 2001). Isoprenoids are composed of C 5 isoprene units and are classified as
hemi-(C 5 ), mono-(C 10 ), and sesquiterpenes (C 15 ) as well as di-(C 20 ), tri-(C 30 ), and tetraterpenes
(C 40 ), and also polyterpenes. Higher polymers are encountered in materials such as
rubber.
Recently, various isoprenoids have attracted commercial interests as nutraceuticals or
biologically active agents with potential health benefits. For example, carotenoids form one
of the most important classes of plant pigments and play a crucial role in defining the quality
parameters of fruits and vegetables. In general, carotenoids such as lycopene and lutein are
profound antioxidants and potential anticancer agents, and β-carotene possesses provitamin
A activity. A diterpene, paclitaxel (Taxol), has been established as a major cytostatic agent
(Eisenreich et al., 2001) and is used for the treatment of certain cancers. Triterpene saponins
present in legumes have several biological functions including hypocholesterolemic, immunostimulatory,
antioxidant, antidiabetic, and antitumor properties. Plant sterols such as
sitosterol, stigmasterol, and campesterol have a similar structure to cholesterol, and have
the capacity to lower plasma cholesterol and LDL cholesterol levels (Piironen et al., 2000).
13.2 Carotenoid accumulation in fruits
The development of red pigmentation is one of the most recognizable features of ripening
in most tomato fruits. The major carotenoids that accumulate in ripe red tomato fruits are
lycopene (∼90%), β-carotene (5–10%), and lutein (1–5%), with trace amounts (