Dates - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 178

(Thompson et al., 1998). The precooling process to
remove field heat can be achieved via different methods
such as forced air-cooling, hydrocooling, vacuum cooling,
top icing, and room-cooling methods (Elansari, 2007). The
deficiency, abuse, or fluctuation of the cold chain (temper-
ature and RH) not only increases the deterioration of the
product but can also trigger safety problems. High or fluc-
tuating temperatures can increase product senescence and
decay and therefore increase losses; it can also increase
RH and may cause water fluctuation, especially in pack-
ages, which greatly increases the proliferation of spoilage
microorganisms. Other technical problems include pack-
ing, packaging, transport, markets and marketing, quality
control and assurance, hygiene, and food safety (Yahia
et al., 2005). Water cooling (also known as hydrocool-
ing), is a rapid and less expensive method. However, not
all kinds of products tolerate hydrocooling, and it there-
fore might be used for Bisir but not for Ta m a r stage. The
hydrocooling process with ice-water mixture is a very ef-
fective method to precool dates to extend the shelf life
and maintain quality during the chain of transportation
(Elansari, 2007).
The FAO has conducted several activities to prolong
the storage of dates using refrigeration or freezing. The
process is mainly based on the slowing down fruit matu-
rity (i.e., Khalal, Rutab, and Ta m a r ). The vast majority of
dates are harvested at full maturity ( Ta m a r stage) when the
color and sugar content characteristic of the cultivar has
fully developed. Also, Ta m a r stage fruit has the longest
potential storage life (many months) compared to Rutab or
Khalal (several weeks maximum). In the case of fresh dates
harvested at the Ta m a r stage, storage at − 18 ◦ C provides the
maximum extension of shelf life (up to 1 year) and preser-
vation of edible product quality (FAO, 2008).

ing injuries (Al-Ani, 1985). The fruits which contain high
soluble solids like dates (Booij et al., 1995) exhibit low sen-
sitivity to freezing injuries. The two stages of Rutab (early
and late) responded positively to the storage temperatures.
However, the varietal difference for the storage was more
noticeable than the stage of maturity. Both the storage tem-
peratures (-10 ◦ C and -20 ◦ C) could be used without greatly
affecting the quality of the dates, except the color at − 10 ◦ C
was darker and the texture was softer than at -20 ◦ C.
Alhamdan et al. (2005) utilized three methods to freeze
Rutab; individual quick freezing (IQF), cryogenic freezing
using nitrogen stored at − 40 ◦ C, and traditional slow freez-
ing stored at 20 ◦ C for 12 months for Barhi cultivar at Bisir

( Khalal ) stage of maturity (blanched and nonblanched), and
'Khlass' at fully ripe ( Rutab ) stage of maturity. Blanching
was done by immersion in hot water at 80 ◦ C for 90 sec,
followed by sudden cooling to minimize the heat dosage to
fruit. There was a considerable variation of freezing time;
average of 10 min for nitrogen system, 80 min for IQF, and
5,400 min for traditional freezers. Frozen dates using IQF
and cryogenic freezing were solid and completely frozen,
especially those produced from cryogenic freezing. How-
ever, slow frozen fruits were still soft in texture and could
not be categorized as completely frozen fruits. Fruits frozen
(blanched and non-blanched) by IQF and cryogenic were
similar in quality to the fresh ones. The average values of
the texture profile analysis (firmness, cohesiveness, springi-
ness, adhesiveness, chewiness, and resilience properties)
showed that non-blanched Barhi cultivar attained the high-
est values of those properties compared with the 'Khlass'
cultivar. In general, the fresh fruits had much higher values
than that of frozen thawed fruits. Blanching was effective
for traditional freezing of Barhi fruits but was not effec-
tive with IQF and cryogenic freezing. Enzyme activities
(PPO and POD) were suppressed by blanching treatment
of Barhi fruits that were frozen by traditional freezing at
-18 ◦ C. (Alhamdan et al., 2005).

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Refrigerated and frozen storage of Rutab
Freezing and cold storage of Khalal has received signifi-
cant attention in recent times when in the date producing
countries domestic refrigeration and cold-chain distribu-
tion of foods has increased exponentially. Khalal dates dif-
fer from the commonly known delicious fruits in that they
do not store well over prolonged periods above freezing
temperatures like apples or oranges (Abboudi and Thomp-
son, 1998). Under proper refrigerated storage, such dates
can be exported and marketed all year round. A tempera-
ture of 0 ◦ -1 ◦ C is recommended for temporary holding of
Rutab, with a RH of 95-100% to prevent wilting or drying.
Rygg and Furr (1953) recommended a storage temperature
of

Effect of thawing on Rutab quality
Hassan and El-Sheemy (1989) reported a marked activity
of PPO, POD, and pectin methyl esterase (PME) after dates
were thawed. El-Din (1998) reported an increase in con-
centration of sugar on thawing of Daka date variety. On
thawing, the Khalal will within a matter of hours convert
into Rutab, however, turns soft and juicy containing 50
to 60% moisture thus making it very tender and difficult
to handle. Moreover, the maturation process after thawing
proceeds much quicker in the date flesh than in the skin that
remains relatively hard and is not like in a naturally ma-
tured Rutab, thus causing skin peeling off problem. At this
point, one could speculate whether cellulase treatment or

18 ◦ C for 1 year, -3 ◦ C for up to 6 months, and 0 ◦ C
for 1 to 2 months (Snowden, 1990). Dates are not subject
to chilling injuries and have very low sensitivity to freez-

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