Agriculture Reference
In-Depth Information
polypropylene. Date paste is produced from clean-pitted
dates by mixing/mincing in with simultaneous addition of
predetermined amounts of water or steam. Major users of
date paste are bakery sector, confectionery and biscuit fac-
tories, and household consumers (Alhamdan and Hassan,
1999). In processing date paste, the optimum steaming time
is 3-5 min and soaking time is 5-10 min at 25 C. A moisture
content of 23% (0.06 a w ) is considered the lowest safe limit
for microbial spoilage. Hysteresis is apparent in date paste
isotherm and over entire relative humidity range (Yousif
et al., 1991a). Ascorbic acid or a combination of ascorbic
and citric acid is effective in keeping the changes in the pH
of the date paste stored at 25 C at a minimum (Yousif et al.,
1991b). However, organoleptic evaluation of the acidified
date paste showed that the addition of more than 0.2% citric
acid was not desirable due to the acidic taste. A pH value
of 5.4 or more was not desirable (Yousif et al., 1991a).
Moreover, the date paste retained an acceptable color for
16and8weekswhenstoredat5 and 25 C, respectively.
Moisture loss is considerable in the polyethylene-packed
date paste after 16 weeks' storage. Storage time causes a
marked and gradual increase in the hardness of the paste.
Viscosity and water activity are slightly affected by stor-
age time. Storage time did not affect the sorption isotherm
of the date paste at low and medium RH (7-75%) (Yousif
et al., 1991b).
Sanchez-Zapata et al. (2010) reported that date paste
('Medjoul' variety) had a high content of sugars (53%)
especially reducing sugars (fructose and glucose), total
and insoluble dietary fiber (7% and 4%, respectively),
and natural antioxidants (polyphenol content; 225 mg
GAE/100 g).
The dryness and hardness of date paste were reported
to be main problems facing the producers of date paste.
Changes of the mechanical properties of untreated date
paste with the passing time as been reported (Al-Hamdan
and Hassan, 2003). Experiments were carried out by Al-
Abid et al. (2007) to overcome the solidification of date
paste. Exposure to steam for 10 min was recommended
based on moisture, pH, compression force, color space, and
water activity in addition to sensory evaluation preference.
To overcome dryness and hardness problem, water or oil
can be added. However, this practice leads to a low-quality
final product.
Another problem that producers of date paste face is the
degradation of color. Alhamdan and Hassan (1999) reported
that water sorption isotherms of date pastes of three date
cultivars, 'Ruziz,' 'Khudari,' and 'Khalas' were highly de-
pendent on temperature, while dependence on cultivar type
was not as strong.
Chemical and microbiological properties of organic and
conventional date pastes produced from the 'Deglet Nour'
cultivar were investigated by Mrabet et al. (2008). Sig-
nificant differences were observed in water content, sugar
profiles, and pH among the date pastes. The low mois-
ture and the high acidity of organic date paste were two
important positive attributes for its storage and potential
manufacturing uses. Considerable interest has developed
on the preservation of conventional date paste by the use
of natural additives such as Juniperus phoenicea and olive
oil (conditioned paste) after pasteurization, which results
in 95% mold CFU's reduction and 84% reduction for the
yeast populations, after 45 days at 25 C.
Date syrup
The low-quality date is used to produce date syrup (Date
concentrate) since it is a good source of glucose and fruc-
tose. Sucrose is present in significant amounts as well.
Sugars are responsible for much of the physical nature of
syrups as well as its hygroscopy (Tavakolipour and Kalbasi-
Ashteri, 2007). Date syrup could replace sugar in cases
where the problem of color is not important.
Chemical nature of date syrup
Color of date syrup is from light to dark brown. The high
acidity level in date syrups (pH 3.4 to 4.0) contributes to
their stability against microorganisms. Beside sugars, date
extract contains different amounts of pectin, proteins, min-
erals, and hemi cellulose substances (Aligedi and Beshkov,
1976). Presence of pectin causes remarkable increase in
date syrup viscosity. Their presence retards the rate of fil-
tration and renders clarification of the date extract quite
difficult. Proteins have the same effect. The elimination of
protein and pectin need specific materials having the ability
to adsorb such colloidal matters (Ehrenberg, 1977). Crude
protein and ash contents of the date syrups are in the same
trend of their fruits. Date syrups are rich in sodium, potas-
sium, calcium, magnesium, and iron. Date syrups show a
low sodium-potassium ratio (1:8.3) especially important for
those who have diets with a restriction on sodium intake.
Moisture content is a major factor that determines the keep-
ing quality of syrups since it bears a direct relation to the
likelihood of undesirable fermentation (Aleid et al., 2007).
Date syrup extraction by hot water
Dates are placed in a vessel and the required amount of wa-
ter is added. The temperature of the mixture is adjusted and
is mixed for a given time period. The rate of mixing is kept
constant. The vessel is covered to minimize the evaporation
loss of water. At the end of the run, the mixture of sugars
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