Antioxidants and Bioactive Compounds in Fruits - Fruit Ripening: Physiology, Signalling and Genomics - page 105

for the classifi cation of terpenes, as shown
in Table 7.1 (Graßmann, 2005).
Terpenes of low molecular weight are
components of essential oils such as
limonene, pinene, linalool, etc. (Bakkali, et
al. , 2008). The most interesting triterpenes
are oleanolic and maslinic acid with high
potent biological activities (Kontogianni, et
al. , 2009). In addition, limonoids such as
limonin, nomilin and nomilinic acid are
found in citrus fruits and are the most
well-known tetraterpenes (Manners, 2007).

physiological and pathological processes
including immune responses, cardio-
vascular

disease and tumorigenesis

(Radomski et al. , 1990).
In higher plants, besides a role in
protein synthesis, arginine is utilized as
nitrogen storage in seeds immobilized
during seedling growth (Chen et al. , 2004)
and as a precursor for biosynthesis of
polyamines via arginine decarboxylase,
proline, nitric oxide and plant alkaloids
(Delauney and Verma, 1993; Crawford,
2006). Beyond its apparent role in
metabolism, arginine is involved in many
physiological processes including abiotic
stress responses. Arginine participates in
the detoxifi cation of plant tissues from
overaccumulation of ammonia during stress
(Rabe and Lovatt, 1986). Other metabolites
further up the arginine biosynthetic path-
way such as citrulline and ornithine have
also been associated with stress resistance.
Citrulline is involved in resistance to
hyperosmotic stress acting as a hydroxyl
radical (˙ 2+ ) scavenger (Takahara et al. ,
2005). Ornithine is also a precursor of
polyamine biosynthesis via ornithine
decarboxylase, which is also involved in
stress resistance by stabilizing cellular
structures (Tiburcio et al. , 1994; Handa and
Mattoo, 2010), acting as a scavenger of ROS
and as an osmolyte (Nambeesan et al. ,
2010), and having important biological
functions in human physiology and the
prevention of certain diseases (Kalac and
Krausova, 2005; Larqué et al. , 2007).
Polyamines occur in a variety of fruits and
vegetables, with putrescine scoring the
highest values among the other polyamines,
namely spermidine and spermine (Mattoo
et al. , 2010). Different citrus fruit (oranges,

7.2.6 Other bioactive compounds

Arginine

Arginine is an important amino acid in
human nutrition. It is an essential amino
acid for the fetus and neonate and a
conditionally essential amino acid for
adults (Wu et al. , 2000). An increasing
number of medical surveys support the
benefi cial effect of a diet rich in arginine
(Flynn et al. , 2002, and references therein).
This amino acid appears to be a powerful
mediator of multiple biological processes,
including the release of several hormones,
collagen synthesis during wound healing,
antitumor activity, immune cell responses
and the prevention of cardiovascular
diseases (Lewis and Langkamp-Henken,
2000; de Nigris et al. , 2003; Grillo and
Colombatto, 2004; Hayashi et al. , 2005;
Arnold and Barbul, 2006). Arginine is also
the precursor in nitric oxide synthesis in
vascular cells (Palmer et al. , 1988). Nitric
oxide is a ubiquitous signalling molecule, a
cytotoxic free radical and a neuro-
transmitter, and is involved in many

Table 7.1. Classifi cation of terpenes.
Number of carbons Isoprene units Subgroup

10 2 Monoterpenes

15 3 Sesquiterpenes

20 4 Diterpenes

25 5 Sesterterpenes

30 6 Triterpenes

40 8 Tetraterpenes