Agriculture Reference
In-Depth Information
invert sugar, a variety-dependent process (Ahmed et al.,
1995). At this stage, tannins rapidly precipitate and lose
their astringency, fruits become palatable, and browning of
the skin and softening of the tissues appear. The moisture
content goes down to about 35%, and the dates at this stage
are sold as fresh fruit, however, the fruit is still perishable.
Dates in the Rutab stage are the most desirable since they
are at the softest and sweetest stage (Sawaya et al., 1983;
Barreveld, 1993; Myhara et al., 1999).
COMPOSITION
Proximate composition
Knowledge of the qualitative and quantitative chemical
composition of date fruit is of prime importance to the
use of dates, in particular the packer, processor, or trader,
because it affects the possibilities and limitations of the raw
material for the intended end use. Inayatullah et al. (1989)
and Jabbar et al. (1988) reported that fresh dates of 20%
moisture content contained 60-65% sugars, 2.5% fiber, 2%
protein, less than 2% fat, and some mineral matter and
pectin substances. In another report, a high percentage of
carbohydrates (total sugars) (44-88%), fat (0.2-0.5%), 15
salts and minerals, protein (2.3-5.6%), vitamins, and a high
percentage (6.4-11.5%) of dietary fiber was reported by Al-
Shahib and Marshall (2003). The changes in composition
are variety-dependent.
Ta m a r stage
The final stage of fruit maturation is the Ta m a r stage, which
occurs approximately 31 weeks after pollination. The fruit
is palatable and has an attractive biomass. The fruit main-
tains a soft texture with a sweet taste. It has lost most of
its moisture, and its flesh has firmed but is pliable. The
fruit at this stage is of brown color; is universally known
as 'date' dried fruit; contains the least amount of moisture,
with about 25% moisture content; and is self-preserving
(Dowson, 1982; Myhara et al., 1999), with acidity levels
from 0.03% to 0.3% as citric acid (Elahmer et al., 2007).
The tannin content is at its lowest level (Sawaya et al.,
1983). The fruit at this stage is somewhat preserved, and
microorganisms will not be able to grow on it but not ex-
empted from insect infestation, moisture uptake, and com-
positional changes (darkening and changes in flavor) during
subsequent storage and hence requires special precautions
to be taken.
Tannins
The astringency found in green dates is commonly at-
tributed to tannins. Different groups of tannins can be found
in fruit (Myhara et al., 1999); two predominant ones are
phenolic acids and condensed tannins. In general, tannins
decrease as the fruit matures, resulting in a corresponding
decrease in astringency (Sawaya et al., 1982, 1983).
Pigments
A number of pigments are present in dates, for example,
carotenoids, anthocyanins, flavones, flavonoles, lycopene,
flavoxanthin, and lutein in fresh Egyptian dates (Barreveld,
1993). Chlorophylls a + b, dominant in the Kimri stage
(Bacha et al., 1987) were completely lost at the end of
the first stage of fruit development that gives rise to the
appearance of the carotenoids. Anthocyanins are present in
relatively smaller amounts in the various stages of fruit de-
velopment, exhibiting higher concentrations when the color
of the skin characterizing the Khalal stage is red (Bacha
et al., 1987).
DATE HARVESTING
Generally, dates are harvested and marketed at three stages
of development: mature firm ( Bisir or Khalal ), full ripe
( Rutab ), and dry ( Ta m a r ). The decision for harvesting at
one or other stage depends on cultivar characteristics; espe-
cially, soluble tannins levels, climatic conditions, and mar-
ket demand (Glasner et al., 2002). The harvesting method is
planned in such a way as to ensure that the fruit has the ap-
propriate texture when it reaches the market. It must be soft
enough to be packaged and marketed with minimal changes
in shape. Its moisture should be 20-26% (when fresh), with
equilibrium relative humidity (ERH) of not more than 65%.
Consequently, dates of
Volatile compounds
Narain (2007) reported 14 esters, 10 alcohols, four lac-
tones, eight aldehydes, and three ketones in the fleshy pulp
of dates. Pentane extracts which possessed strong date-like
aromas were also identified in dates. A total of 36 volatile
components were identified, of which only six were re-
ported previously in dates. Many of these components pos-
sessed aromas and flavors that potentially contribute to the
sensory characteristics of dates, suggesting that a combina-
tion of volatile components is responsible for the desirable
flavor of dates (Reynes et al., 1996).
65% ERH ensure resistance to mi-
crobiological factors such as mold, yeast, and bacteria that
attack the fruit. Therefore, harvesting should take place
while the fruit has a relatively high water content to prevent
the fruit from losing water and becoming hard in texture
(Navarro, 2006).
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