Antioxidants and Bioactive Compounds in Fruits - Fruit Ripening: Physiology, Signalling and Genomics - page 106

mandarins and grapefruit) and juices
thereof and processed foods such as sauer-
kraut, ketchup, frozen green peas and fer-
mented soy products are rich in putrescine,
whereas spermidine content was recorded
as highest in legumes, especially soybean,
pear, caulifl ower and broccoli (Kalac and
Krausova, 2005). Spermine is usually found
in legumes.
We are interested in understanding
arginine biosynthesis and its regulation in
tomato fruit. A single copy of the N-acetyl-
L-glutamate synthase gene ( SlNAGS1 ), the
fi rst gene in arginine biosynthesis, has been
isolated from tomato and overexpressed in
Arabidopsis thaliana under the control of
the 35S promoter. The transgenic plants
accumulated high levels of ornithine and
citrulline and exhibited a higher tolerance
to salt and drought stress compared with
wild-type plants (Kalamaki et al ., 2009).
Recently, all genes in arginine biosynthesis
in tomato fruit have been cloned, and the
SlNAGS1 gene was specifi cally over-
expressed in tomato fruit under the PG
promoter, which resulted in high levels of
arginine in pink and red fruit (Kanellis et
al ., unpublished data).

inhibition of ethylene biosynthesis
(Pezzarossa et al. , 1999). In lettuce and
chicory, Se improved the keeping quality
through the inhibition of ethylene
production and phenylalanine ammonia
lyase activity (Malorgio et al. , 2009). Se
concentrations were increased in peach
and pear fruit by spraying leaves and fruit
with sodium selenate, resulting in an
extended shelf-life of the fruit and delayed
softening (Pezzarossa et al. , 2012).

7.3 Determination of Phytochemical
Content and Antioxidant Potency

The extraction of phytochemicals from
fruit tissues is a prerequisite step for the
quantifi cation of phytochemical content in
fruits. A plethora of extraction methods
such as solid-liquid extraction, Soxhlet,
ultrasound-assisted extraction, pressurized
liquid extraction, supercritical extraction
and microwave-assisted extraction have
been described for recovery of phyto-
chemicals from diverse fruit materials
(Ignat et al. , 2011). The extraction of
phytochemicals is performed using polar
or apolar solvents, depending on the
polarity of the phytochemicals being
examined. The temperature of extraction is
also of critical importance, as it usually
increases the effi ciency of extraction, but
some phytochemicals are degraded at high
temperatures (Galanakis et al. , 2013).
The quantifi cation of phytochemicals is
usually carried out by instrumental
analytical methods. The most common
group of analyses are simple spectophoto-
metric methods that allow measurement of
the total concentration of compounds such
as total phenolics, total anthocyanins or
total carotenoids. These methods are
usually based on a reagent that reacts with
phenols to form chromogens that can be
detected spectrophotometrically, as in the
Folin-Ciocalteu method or the determin-
ation of total AsA using the dye
2,6-dichloroindophenol. Other specto-
photometric protocols exploit the char-
acteristic absorbance wavelengths of a
group of compounds, as Obied et al.

Selenium

Among the mineral elements, selenium (Se)
can be regarded as an essential micro-
nutrient for human health. It exhibits an
antioxidant function, and as such can be
considered as a chemopreventive agent in
cancer and as an important nutrient in the
immune system (Pedrero and Madrid,
2009). This function was attributed to its
participation in the 25 selenoproteins in the
human proteome including gluthathione
peroxidase and thioredoxin reductase
(White and Broadley, 2009; Hasanuzzaman
et al. , 2010).
Generally, Se occurs in low amounts in
plants and fruits, and thus it can affect
their antioxidant properties and chemical
composition, whereas at higher amounts it
can act as a pro-oxidant, resulting in
reduced plant growth (Pezzarossa et al. ,
2012). Selenium can delay tomato fruit
ripening and senescence through the