Harvesting and Postharvest
Technology of Dates
Elhadi M. Yahia1, Maria Gloria Lobo2, and Adel A. Kader3
1Facultad de Ciencias Naturales, Universidad Autonoma de Queretaro,
Avenida de las Ciencias S/N, Juriquilla, Queretaro, Mexico
2Department of Tropical Fruits, Instituto Canario de Investigaciones Agrarias,
La Laguna, Tenerife, Spain
3Department of Plant Sciences, University of California, Davis, CA, USA
Preparation for market:
Transportation to the packinghouse
Quick initial sorting
Responses to controlled atmospheres
Physical and physiological disorders
Disease control strategies
Insect pests and their control
Modiﬁed atmosphere (MA)
Food safety considerations
Dates: Postharvest Science, Processing Technology and Health Beneﬁts, First Edition.
Edited by Muhammad Siddiq, Salah M. Aleid and Adel A. Kader.
2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd.
106 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
Date Palm (Phoenix dactylifera L.) is one of the oldest fruit trees in the world
and is mentioned in the Qur’an and Bible. It produces a berry fruit (date)
that represents the basic food for North Africa, Arabia, and Persia’s peo-
ples, where hundreds of varieties are grown for commercial purposes and are
deeply rooted in their economy, history and culture. It is thought to have orig-
inated in Mesopotamia (Wrigley 1995) from there its cultivation spread to the
Arabian Peninsula, North Africa, and the Middle Eastern Countries. There
is archeological evidence of date cultivation in ancient times (7000 BCE in
western Pakistan; 6000 BCE in eastern Arabia; 4000 BCE in Mesopotamia and
Egypt). In later times, traders spread dates around South West Asia, northern
Africa, Spain and Italy. The Spaniards introduced dates into Mexico and Baja
California in 1765 (Nixon 1951). In 2011 world date production was about
7.51 million metric tons, the leading producing countries being: Egypt, Saudi
Arabia, Iran, United Arab Emirates, Algeria, Iraq, Pakistan, Sudan, Oman,
and Tunisia. The main exporter countries were: United Arab Emirates, Pak-
istan, Iraq, Iran, Tunisia, and Saudi Arabia, while United Arab Emirates,
India, Morocco, France, and Yemen were the major importers (FAO 2013).
Date palms like very hot, dry weather and lots of water on their roots.
Fresh dates are typically marketed at three of the four stages of its growth
and development (Khalal,Rutab and Tamar) and can be consumed soft,
semi-dry or as dry fruits, depending on their water content at harvest when
fully-ripe, or in various processed forms (Sawaya 1986). According to the
tropical and subtropical fruits classiﬁcation shown in Table 5.1, date fruits are
Table 5.1 Respiration rate and ethylene production rates of selected tropical and subtropical
fruits at 20 ◦C.
Respiration rate Ethylene production rate
Class (mg CO2/kg.hr) Fruits (μg/kg.hr) Fruits
Very low <35 Dates, carambola,
Low 35–70 Banana (green), litchi,
0.1–1.0 Pineapple, carambola
Moderate 70–150 Mango, rambutan,
chiku, guava, durian,
1.0–10.0 Banana, guava, mango,
sugar Apple, durian,
High 150–300 Avocado, banana (ripe),
sugar apple, atemoya
10–100 Avocado, papaya,
Very high >300 Soursop 100 Cherimoya, passion fruit,
Source: Paull and Duarte (2011), Gross et al. (2002).
FRUIT DEVELOPMENT 107
non-climacteric fruit, with very low respiration rate and low ethylene produc-
tion, and therefore with very low metabolic activities. They are considered
nutritious and a high-energy food (300 calories/100 g) because they are rich
in: sugars providing quick energy intake (Sawaya et al. 1982, Booji et al. 1992,
Ahmed et al. 1995), minerals (Imad and Abdul Wahab 1995, Haﬁd et al.
2007, Elleuch et al. 2008), vitamins, phenols, ﬂavonoids, anthocyanins and
carotenoids with functional properties (Al-Farsi et al. 2005a, Haﬁd et al. 2007,
Biglari et al. 2008, Al-Turki et al. 2010). The soluble ﬁber helps against consti-
pation (Kulkarni et al. 2008), and the low level of fat high in omega-3, omega-
6, and oleic acid, is heart-healthy. The antioxidant properties of date fruits
vary depending on the amount of phenolics, vitamins C and E, carotenoids,
and ﬂavonoids present (Al-Farsi et al. 2005b, Mansouri et al. 2005).
Losses during harvesting, postharvest handling and marketing are high due
to the incidence of physical and physiological disorders, pathological diseases
and to insect infestation.
Date fruit development goes through four maturity/ripening stages: Kimri
(Khimri), Khalal,Rutab, and Tamar (Tamr). Dates take 5 to 7 months from
the time they ﬁrst emerge from the spath, bunch or casing until they are fully
At 19 weeks after pollination, the fruit reaches the ﬁrst stage called Kimri.
When picked at this point, dates are small, green, with a hard texture and non-
edible. Moreover, they cannot be ripened artiﬁcially beyond a low-quality
Khalal stage. At the Kimri stage, there is a rapid increase in size, weight, and
reducing sugars; it is the period of highest acid activity, moisture (80%) and
tannins content (Sawaya et al. 1982, Myahra et al. 1999).
The second stage, Khalal (Bisir), occurs approximately 25 weeks after pol-
lination. Dates color is yellow or red according to variety, sucrose content
increases, moisture content goes down (60%), and tannins start to precipitate
and lose their astringency; although some consumers ﬁnd them still astringent
(Table 5.2). In some varieties, e.g., Barhi (Barhee, Berhi), Hayani, Samany,
Table 5.2 Fruit characteristics at different development stages (Kimri,Khalal,Rutab,and
Attribute Kimri Khalal Rutab Tamar
Edible No Yes Yes Yes
Color Green Yellow/Red Partially browned Amber/Dark brown
Texture Hard Hard/Crisp Softened Soft/Chewy
Moisture 85% 50–85% 30–40% 20–25%
Sucrose ++++ +++ ++ +
Reducing sugars + ++ +++ ++++
Tannins ++++ +++ ++ +
Astringency ++++ +++ ++ +
Storability Perishable Very perishable Perishable Non-perishable
Low ( +), Moderate ( ++), High ( +++), Very High ( ++++).
108 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
and Zaghlol, this latter process evolves rapidly, which makes them palatable
and reach commercial maturity (Barreveld 1993). Since the fruits are very
perishable due to their high sugar and water content which cause fermen-
tation if not refrigerated properly, they must be transported to the market
immediately after harvest (Glasner et al. 2002).
At Rutab stage (29 weeks after pollination), fruit tip starts turning brown,
weight decreases due to moisture loss (about 35%), sucrose is partially con-
verted into invert sugar, tannins precipitate, the skin turns brown and the
tissues soften (Ahmed et al. 1995, Imad and Abdul Wahab 1995). Dates
at this stage become crisp in texture and are sold as fresh fruit, being the
most desirable due to the wide range of ﬂavors, textures, and aromas devel-
oped. Nevertheless, they are still perishable, changing into Tamar stage
within 4–7 days.
The ﬁnal stage of date maturation is the Tamar stage (approximately 31
weeks after pollination). Fruits are fully ripe; very sweet, dark brown or
nearly black, soft and chewy, with the lowest moisture and tannin content
(about 25% and 6%, respectively), rich in reducing sugars (fructose and glu-
cose) and low in sucrose (Sawaya et al. 1983, Aleid et al. 1999). At this
stage microorganisms will not be able to grow on dates, however, moisture
uptake and compositional changes may occur if special care is not taken
Date palm produces about 40 kg fruit annually, with yields of more than
100 kg possible with intensive management. When farmed with low levels of
inputs and poor management, palms may produce 20 kg or less fruit annually.
Female plants start producing dates at 4 to 6 years of age and reach full pro-
duction within 15 to 20 years (Barreveld 1993, Nixon and Carpenter 1978).
The average economic life of a date garden is 40 to 50 years, but some are
productive up to 150 years. Bunches of dates are usually covered (bagged)
with brown craft paper, white paper, or cotton or nylon mesh bags. Awad
(2007) found that the use of black and blue polyethylene bags increased the
rate of fruit ripening and raised Rutab yield per bunch. Bagging can protect
fruit bunches from high humidity and rain, minimize damage from sunburn,
and decrease losses from birds (Nixon and Carpenter 1978, Zaid and de Wet
2002). These cultural practices increase labor input.
Time of harvest is based on date fruit’s appearance and texture, which are
related to moisture and sugar content (Yahia 2004). Most of these charac-
teristics depend on growers’ experience and date use and destination. Dates
for immediate sale are often harvested when moisture content is still high
whereas dates which will be stored are left on the palms for natural cur-
ing to lose excess moisture. Although some cultivars with low tannins and
high sugars can be harvested at the Khalal stage, dates of other cultivars
harvested before full maturity must be ripened artiﬁcially. Very immature
dates cannot be properly ripened artiﬁcially and consequently will be of
poor quality. Deglet Nour fruits should not be harvested before the turn-
ing stage in which the texture is yielding-to-pliable and the color is amber-
to-cinnamon. Fruits harvested with a reddish ring at the perianth end have
better storage potential than fruits left on the palm until the ring has faded
with more advanced maturity (Rygg 1975). Halawi fruits should not be har-
vested before the soft ripe stage. Maktoom and Boufgouss fruits can be har-
vested when 10–25% of the surface is translucent, and then ripened to an
Proper timing of harvest reduces incidence and severity of cracking or
splitting of dates, excessive dehydration, insect infestation, and attack by
microorganisms. Dates are harvested in July to August at the Khalal stage
or in September to December at the Rutab and Tamar stages in northern
hemisphere production regions. In the southern hemisphere harvesting takes
place in February, March and April. Date palms are picked several times
during the harvest season since all dates do not ripen simultaneously. Dates
are harvested at or near maturity. Fruit ripening depends on cultivar, heat
units during the growing season and the stage at which the fruit are picked.
For early-ripening cultivars, the fruit within the bunch may take as long as 3–
4 weeks to complete ripening, while for late-ripening cultivars, fruit ripening
within the bunch occurs in about 8–12 weeks. Early harvest is commonly prac-
ticed to take advantage of higher prices in the market and to avoid adverse
weather conditions, cracking or splitting of fruits, excessive dehydration in
early maturing fruits, insect infestation, and microorganism attack. As ripen-
ing of dates is progressive on the bunch some fruits can overripe while others
are still at the Khalal or Rutab stages. Selective picking of individual dates
or strands is often practiced for good quality at prime maturity. When this
approach is adopted, a number of pickings are made before harvesting all
fruits. The common method is to harvest by bunch when the majority of dates
Harvest is generally done by hand, with access to the crown of the tree
being by way of climbing or mechanical lifts. As the palm tree grows taller,
harvesting the dates becomes more difﬁcult, dangerous and more costly.
Hand-harvesting of dates (Figure 5.1) involves the use of aluminum lad-
ders for short palms and picking platforms for taller palms. Ladders may be
mounted on the palm tree to facilitate harvesting or various types of lifts,
such as tree squirrel and self-propelled elevating platform, are used to elevate
the harvesting laborers to facilitate harvesting. The fruits are placed within a
bucket and lowered to the ground, and then packed in bulk bins and sent to
the packinghouse. A usual procedure to climb the date palm trees is the use
of a wide belt woven out of coir to support the climber’s back and cutting
off the whole bunch. Bunches may be lowered either by ropes or by passing
the bunch hand-to-hand. Fruits are also harvested by shaking the bunch and
all mature fruits which detach easily drop onto mats spread on the ground
around the palm. Very soft fruits can be damaged in this process. Mechan-
ical aids for harvesting have been used extensively in the USA, Saudi Ara-
bia (Alhamdan 2006) and United Arab Emirates. Only dry types dates are
110 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
Figure 5.1 Manual harvesting of dates in Saudi Arabia (top) and Egypt (bottom). Reproduced
with permission of Atef Elansari and Awad Hussein. (For a color version of this ﬁgure, please
see the color plate section).
suited for mechanical harvesting as the softer types of date can be damaged
by improper harvesting. Frequency of picking depends on several factors such
as type of date (soft, dry or semi-dry), climatic conditions, market demands,
handling methods, cost of handling, and availability and cost of pickers.
Hand harvesting can reach as much as 45% of the operational costs,
and therefore efforts were made to develop mechanical harvesting meth-
ods to carry out the harvesting more conveniently and faster than traditional
method (by hand) (Al-Suhaibani et al. 1991, Ibrahim et al. 2007). Some trials
have been carried out on Deglet Nour dates in the Coachella valley, Califor-
nia, using platforms built on extensible towers, enabling the picker to move
from one palm to the other (Brown 1982). However, picking is done by hand,
as in the hand harvesting procedure. Later, the concept of mechanical har-
vesting of mature fruit bunches was developed, in which whole bunches were
cut off on two occasions. A later development was the use of mechanical
shakers, in which the fruit bunch axis was shaken and fruit collected under
the tree. Mechanical harvesting was found to reduce the operating cost of
harvest to 25%, as well as cutting down the cost of handling and packing by
Figure 5.2 Hydraulic-crane built on a truck used by the picker to reach the top of the tree.
Reproduced with permission of Davis Karp.
60%. Accordingly, mechanical harvesting method of cutting off the whole
fruit bunches and then using mechanical shakers to remove the fruit became
the standard procedure in the Coachella valley, California. A later develop-
ment was the use of a hydraulic-crane built on a truck and the crane had a
basket used by the picker to reach the top of the tree (Figure 5.2). The picker
cuts off the whole bunch and places it in the basket, which is lowered down
by the crane to a shaker-trailer for shaking. After shaking, fruits fall into the
bulk bins placed beneath the shaker-trailer. The bulk bins are then lifted by
a shufﬂe and placed in trucks to be transported to the packinghouse. Almost
80% of dates produced in USA are harvested by this method, which reduced
the operating costs by 50% (Rygg 1975, Brown 1982, Hodel and Johnson
A few date cultivars, such as Barhi (Barhee, Berhi), Hayani, Samany, and
Zaghlol, are harvested at the Khalal stage (partially-ripe) when they are
112 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
yellow or red (depending on cultivar), but many consumers ﬁnd them astrin-
gent (due to high tannin content). Ripening of Khalal stage dates can be has-
tened by bagging bunches during growth. After harvest, these dates can be
ripened to the Rutab stage by either quick freezing and keeping at –18 ◦Cor
lower temperatures for at least 24 hours and thawing them, or by exposure
to acetaldehyde or ethanol vapors. Most dates are harvested at the fully-ripe
Rutab (light-brown and soft) and Tamar (darkbrown and soft, semidry, or
dry) stages, when they have much greater levels of sugars, lower contents of
moisture and tannins (disappearance of astringency), and are softer than the
Khalal stage dates. Moisture contents of Khalal,Rutab, and Tamar dates are
45–65%, 30–45%, and <30%, respectively (Kader and Hussein 2009).
Khalal (Bisir) dates are sometimes marketed on branches (strands) or
bunches (Figure 5.3). The whole bunches are harvested when the dates are
fully yellow and lowered to ground level, then hung on a carrier for trans-
portation to the packinghouse or to the market. Green to greenish-yellow
and ripe (Rutab) fruits are removed from the branches before packing for
shipment to markets. Date bunches are usually covered with net covers to
collect the fallen ripe fruits.
Figure 5.3 Khalal stage Deglet Nour dates on bunches for sale in Tunisia. Image by E.M. Yahia.
(For a color version of this ﬁgure, please see the color plate section).
ARTIFICIAL RIPENING 113
Figure 5.4 Deglet Nour dates at Tamar stage after harvesting in bunches are shaken into bins
to remove ripe fruit. Reproduced with permission of Davis Karp. (For a color version of this
ﬁgure, please see the color plate section).
Ripening rate of Khalal stage dates can be increased by preharvest ethrel
application, either in spray or injected into the bunch peduncle. Moreover,
postharvest dipping of fruit at the Khalal stage in ethrel and abscisic acid or
ethanol vapor has been shown to hasten date ripening (Awad 2007).
Rutab and Tamar dates are harvested as whole bunches when the majority
of dates are ripe, which are lowered to ground level and shaken into a bin or
harvested bunches are shaken to remove the ripe dates (Figure 5.4). Alterna-
tively, individual ripe dates are picked from bunches and, on average, three
pickings are required over several days. Pickers use different types of contain-
ers and harvesting aids to lower the dates to ground level. Fallen dates on the
ground, which are subjected to higher mechanical damage, should never be
collected and sold for human consumption because of the increased chances
for microbial contamination and embedding of soil into the ﬂesh when the
dates touch the ground (Kader and Hussein 2009).
Dates picked immature to avoid damage by rain, insects or other factors need
to be ripened after harvest. In some African countries where the weather is
114 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
hot and the air sufﬁciently dry, harvested immature fruits are ripened out-
doors. Although this technique is simple and cheap, the exposed fruits are
subjected to adverse conditions such as rain, dust from winds, bird attack,
rodents, etc, and ripening conditions cannot be controlled.
For indoor ripening, rooms should be equipped with devices to control
temperature and humidity and an adequate air circulation. The exact tem-
perature and time of ripening depends on the type of date, stage of matu-
ration and condition at harvest. A temperature of 40–43 ◦C is recommended
for ripening Khadrawy, Kustawy, Hayani, Sayer, Khalas, and Sphinks dates
(Hyde 1948). Temperatures of 45–46 ◦C and 70% relative humidity for a
period of 2–4 days or longer are required to ripen cultivars with thick ﬂesh
such as Iteema, Maktoom, and Saidy. Deglet Nour dates should not be
ripened at temperatures above 35 ◦C (to avoid fruit darkening and ﬂavour
loss). Soft cultivars such as Halawi, Dayri, and Zahidi can be ripened at
slightly higher temperatures (35–38 ◦C). Ripening of these cultivars is com-
plete in about 2–4 days when they have lost their translucency and little or no
hard tissue remains. Use of higher temperatures is not recommended because
it increases skin separation from the ﬂesh of the dates. Normally, date ripen-
ing takes 2–5 days depending on their ripeness stage at harvest, temperature,
and relative humidity.
Ripening enhancement of Khalal stage dates can be achieved by treatment
with acetic acid, ethanol, or acetaldehyde. Other techniques and chemicals
have been tested for ripening dates. Dipping fruits of cv. Khasab, widely
grown in Saudi Arabia, in 1% NaCl plus 2% acetic acid resulted in good qual-
ity fruits after ripening (Asif and Al-Taher 1983). In general, ﬂavor quality of
dates ripened after harvest is lower than those ripened on the tree.
Low temperatures, such as freezing for at least 24 hours, can be used to
accelerate ripening of Khalal dates to Rutab stage. Freezing at –35 ◦Cto–
50 ◦C, which causes less damage to the tissues, is better than freezing at –1 ◦C
to –18 ◦C, which causes some damage to cell membranes and walls (Kader
and Hussein 2009).
Dates need to be dehydrated to the optimal moisture content for preserving
their quality during subsequent handling and storage. The temperature and
duration required to reduce water content depend on the type of date, use
and ﬂesh consistency. Drying conditions such as drying temperature, relative
humidity and drying time will affect color, ﬂavor, shrivelling, separation of
skin and ﬂesh, and overall acceptability. Dehydration is an operation that
aims to achieve an appropriate sugar:water ratio, which should be close to
2 for soft dates, greater than 2 for dry dates, and lower than 2 for very soft
dates. This ratio is a good indicator of date quality behavior in storage. Over-
drying to less than 20% moisture should be avoided to keep the dates soft.
The desired moisture content is 23 to 25%.
In countries with low air humidity, dates can be dehydrated using solar
energy by spreading the dates on trays that will be exposed to the sun or
under plastic tunnels until drying is completed to the desired moisture level.
Dates are either kept in or separated from the bunch. Alternatively, ambient
air can be forced through the dates spread on stacked trays within a pallet
that is covered by a shrink ﬁlm with ventilation openings at the top and bot-
tom of the pallet. Similarly, ambient-air drying can be done within plastic
greenhouses with good air circulation. Drying in plastic houses that can be
constructed at a reasonable cost, protect the dates from dust, birds, rodents,
and other damaging factors.
If solar or ambient-air drying is not possible, heated air can be used to
dry the dates to their desired moisture content. Conventional drying requires
high temperatures and long times. Final products are characterized by low
porosity and high apparent density values. Vacuum-dried materials had bet-
ter quality retaining nutrients and volatile aroma but the cost of the process
Dehydration is also achieved by exposing dates to hot air (<70 ◦C) inside
a solar or industrial oven to avoid browning of sugars. For drying soft dates,
54 ◦C at 50% relative humidity is recommended, while drying time depends
on initial moisture content. Processing dates by blanching in water at 96 ◦C
and subsequent dehydration at 60 ◦C for 18–20 hours resulted in good quality
of dehydrate dates as compared those without heat treatment (Kulkarni et al.
Sometimes dehydration is carried out simultaneously with ripening until a
safer level of moisture content is reached. This process is commonly accom-
plished by recirculating air until high humidity builds up and then introducing
fresh preheated air at very low humidity.
If picked ripe and not over-dried, dates do not require hydration. However,
sometimes hydration is used to soften the texture of some hard-type date cul-
tivars. It is achieved by dipping dates in hot or cold water for a certain period
of time. Dates are dipped in hot water or exposed to steam at 60 to 65 ◦C
and 100% relative humidity for 4–8 hours (Yahia and Kader 2011). Steaming
for 10 minutes is enough for some cultivars such as Fardh (Fard). Hydration
changes the dried dates into plump and glossy dates. Forced air circulation
is used to improve uniformity of temperature and relative humidity through-
out the hydration room. In addition, this treatment is effective in controlling
some microorganisms and keeping fruit quality. A treatment commonly used
in California for Deglet Nour dates consists of introducing steam at 5 psi until
the temperature reaches 60 ◦C for 4–8 hours. In Algeria, the treatment con-
sists of a temperature of 65–70 ◦C and 55% relative humidity for 24 hours.
High acidity dates are difﬁcult to soften by hydration and acidity during the
process changes very little unless neutralizing agents are added. The addi-
tion of alkaline ammonium sulﬁte during hydration improves the quality of
116 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
hydrated dates that are characterized by moderately high acidity (Rygg 1975).
Dates can be pasteurized by exposure to 72 ◦C and 100% relative humidity
air until their ﬂesh temperature reaches 66 ◦C, where it is kept for 1 hour.
However, such conditions may induce color darkening of the dates.
Preparation for market: postharvest operations
Good handling practices during and after harvesting can minimize mechani-
cal damage and reduce subsequent wastage due to microbial attack.
Transportation to the packinghouse
The harvested fruit is transferred into large plastic or wooden bins for trans-
port to the packing station. Each container contains 200–450 kg of fruit and
is suitable for dry fruit. Large wooden, plastic, or cardboard cases of various
sizes are also used, as well as baskets, sacks (for very dry fruit), and trays,
focusing on the need to prevent damage to the fruit (especially to soft and
sensitive fruit). The fruit must be transported carefully in the early hours of
the morning to avoid the heat and refrigeration during transport is advisable.
Those varieties marketed on the branches must not be shaken during trans-
portation in order to prevent the fruit from falling off the branches. Speedy
transport will also prevent infection by pests which attack the fruit during the
Quick initial sorting
The ﬁrst postharvest handling operation consists of separating ripe dates from
immature ones or from those that have been damaged during harvesting, by
insects, birds, rodents, transport, etc.
Dates arriving from the farm may be contaminated with dirt, dust, and sand
particles, plant/ﬁeld debris, and chemical products and should be cleaned to
remove these particles, which stick to the date skin. Cleaning can be achieved
by blowing air on the fruits and brushing the dates softly to avoid damage to
the fruit skin or by washing the fruits with running water. Dates can also
be cleaned by passing them over damp toweling or with the use of washers.
Spray jets can be used for soft dates instead of washers. Washing with sanitiz-
ers is important to remove soil and debris and for water disinfection to avoid
cross-contamination between clean and contaminated product. Most sanitiz-
ing solutions achieve higher microbial reductions immediately after washing
compared to water washing, however, after storage, epiphytic microorgan-
isms grow rapidly, reaching similar levels. Despite the general belief that san-
itizers are used to reduce the microbial population of the produce, their main
effect is in maintaining the microbial quality of the water.
PREPARATION FOR MARKET: POSTHARVEST OPERATIONS 117
Figure 5.5 Manual sorting of dates on a conveyer belt. Courtesy A.A. Kader.
Air-drying is designed to result in moisture content of 20% or below to pre-
vent growth of molds and yeasts. Temperatures of 55–65 ◦C for drying of soft
dates are generally used (Barreveld 1993). The conveyer speed in the drying
tunnel must be controlled to achieve consistent results.
Dates are sorted to remove culls and to separate them into uniform sizes.
Sorting can be carried out manually or mechanically in crates or on moving
belts (Figure 5.5). Dates can be sorted according to maturity, ﬂesh consis-
tency, color, shape, and size. Within different groups, dates are separated
based on quality. Discarded fruits consist of dates with defects and abnor-
malities such as parthenocarpic (virgin or non-pollinated) fruits, immature
or overripe fruits, fruits mechanically damaged during harvesting or on the
palm, fruits damaged by birds or insects, and fruits with physiological disor-
ders or diseases.
This operation is done manually or mechanically to separate dates based on
their size and weight. Uniformity of size in a package is one of the quality
criteria for dates. Date size varies depending on cultivar. Medjhool dates in
the USA are classiﬁed into three size categories: Jumbo for less than 10 dates
118 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
per pound, Mixed for 10 to 15 dates per pound, and Conventional grade for
more than 15 individual dates per pound.
In postharvest operations date sorting and grading processes can greatly
delay packaging and marketing of fruit. The reason is that they are repetitive,
labor intensive, and time consuming processes and are carried out by humans
manually through visual inspection (Al Ohali 2011). Raji and Alamutu (2005)
reported that intensive research is being conducted to design and built intel-
ligent, reliable, ﬂexible, and effective systems that can quickly sort a variety
of fruit and other agricultural produce; feasibility and applicability of such
a system are being explored on an increasingly basis to improve quality and
economics. Thus, color, size, surface defects, and texture are external charac-
teristics used in sorting and grading in date industry.
Color is an important factor in distinguishing between acceptable date
fruits and damaged or immature dates. Nevertheless only a few research
papers have focused on applying machine vision technique studying each date
variety solely. Wulfson et al. (1989) used a color camera to capture date fruit
images to determine the relative reﬂectance in the range of 400–1000 nm for
good and defective dates. They noted that the red band image was most effec-
tive for detecting defective Majhul (Medjhool) dates, while the green band
image performed best for Zahidi dates.
Al-Janobi (1993) reported a machine vision system to grade date fruits
(Deglet Nour variety) into quality classes based on color and texture anal-
ysis. Later on, in 1998 Al-Janobi applied a line scan based vision for inspect-
ing fast moving dates capable to determine the color/quality of the fruits and
in 2000 developed a computer vision system based on color threshold tech-
nique for grading Sifri variety of date fruits. Fadel et al. (2001) designed a
machine with the capability to differentiate between various date varieties as
well as estimating sugar content of each variety. They carried out a study for
date fruits to ﬁnd out the color properties of different cultivars using (red,
green, blue; RGB) color space to measure the color variation. Their work
showed that color luminosity and red, green, and blue color space can be
used to ﬁnd out color properties of different dates varieties. Lee et al. (2008)
developed a machine vision system, for automatic date quality evaluation for
commercial production, using reﬂective near-infrared imaging (NIR) to eval-
uate date quality by analyzing two-dimensional images. Relative to manual
grading, the operational system results in improved grading accuracy and a
substantial reduction in operating costs.
Al Ohali (2011) designed and tested a prototype computer vision based on
date grading/sorting system by a deﬁned set of fruits external quality features
(Figure 5.6). The system uses RGB images of the date fruits. A computer-
mediated fruit quality assessment and sorting system has two subsystems: a
computer vision system and a fruit handling system. The computer vision sys-
tem captures the image of the underlying fruit and transmits it to an image
processor. The processor, after processing the image, presents it to a pattern
recognizer. The recognizer performs the quality assessments and classiﬁes
the underlying fruit into prespeciﬁed quality classes, and directs the sorter
PREPARATION FOR MARKET: POSTHARVEST OPERATIONS 119
Figure 5.6 Typical layout of a computer-aided fruit sorting system. Source: Al Ohali (2011).
Reproduced with permission of J KSU Comp Info Sci.
to direct the fruit to the appropriate bin. Based on the extracted features
the system classiﬁes dates into three quality categories (grades 1, 2, and 3)
deﬁned by experts (Figure 5.7). The system can sort dates with 80% accuracy
(Al Ohali 2011).
This process is also carried out simultaneously with the grading or sorting. It is
done for the sake of identifying any outside metal particles or items that could
have been picked up with the crop. It is highly recommended for dates to
pass through a metal detector since metals could prove to be highly injurious
during chewing of dates,
This process is done to reduce stickiness and/or improve appearance of the
dates. Several materials have been recommended for this purpose includ-
ing a 5 or 6% solution of soluble starch as a dip, 3% methyl cellulose, or a
combination of 2% butylated hydroxyanisole, 2% butylated hydroxytoluene,
6% vegetable oil, 90% water and a wetting agent (Ait-Oubahou and Yahia
1999). Surface coatings with wax or other materials (such as vegetable oil,
(a) (b) (c)
Figure 5.7 Blemished and graded date fruit: (a) birds ﬂicks, (b) bruises/cuts, and (c) from left
to right – grades 1, 2, and 3 date samples. Source: Al Ohali (2011). Reproduced with permission
of J KSU Comp Info Sci. (For a color version of this ﬁgure, please see the color plate section).
120 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
glucose syrup, corn syrup, date syrup, sorbitol, or glycerol) are also widely
used (Kader and Hussein 2009).
Packaging protects dates from physical damage, moisture absorption or loss
and insect reinfestation during subsequent storage and handling steps. Date
packages are of several types and sizes. Some dates are marketed in 15-pound
ﬂats of ﬁberboard or wood (6.8 kg, approximately), others in 5- or 10-pound
cartons (about 2.3 and 4.5 kg, respectively). Large reinforced cartons are used
for packing dry dates, especially for export. Consumer packages in a number
of sizes and shapes are widely used for dates (Figure 5.8). They include trans-
parent ﬁlm bags and trays overwrapped with ﬁlm. Round ﬁberboard cans with
metal tops and bottoms containing 0.5–1 kg are also used. Rigid transparent
plastic containers with a capacity of 0.2–0.3 kg are commonly used. Small
consumer packages are also used such as bags containing about 50–60 g dates
(Ait-Oubahou and Yahia 1999). Barhi variety at the Khalal stage is packed
on branches in cardboard boxes weighing 5 kg in Jordan, Israel, USA, and
Saudi Arabia. Deglet Nour can be packed on branches at the Rutab stage or
unattached when dates are at the Tamar stage.
Data such as weight, country of origin, quality, and date of expiry should
appear on the package labels (Glasner et al. 2002). Additionally, nutritional
labeling, already required on the retail packages by many dates importing
countries, should be added on all retail packages, including those intended
for the local markets.
Figure 5.8 Various retail-size consumer packages of dates. Courtesy A.A. Kader.
PREPARATION FOR MARKET: POSTHARVEST OPERATIONS 121
Cooling of dates to below 10 ◦C (preferably to 0 ◦C) before transportation or
storage under the same temperatures (0–10 ◦C) and 65–75% relative humid-
ity is recommended to maintain quality. Hydrocooling can be used to cool
Khalal dates to near 0 ◦C in 10 to 20 minutes, depending on initial temper-
ature (Elansari 2008), but requires effective disinfection of the water and
removal of excess surface moisture from the cooled dates before packing in
the shipping containers. Use of a perforated plastic liner within the box can
reduce water loss during transportation and marketing.
The temperature and the speed of refrigeration affect physiological phe-
nomena, such as sugar crystallization, caused by the breaking of cell walls or
the tearing of the skin, facilitating the movement of water inside the fruit or
out of it. This fact is connected to the amount of moisture in the fruit. Thus,
the risk increases when the amount of moisture rises above 20% (also in low
temperatures) (Glasner et al. 2002).
Storage and transport at low temperatures is the most important way of main-
taining quality of dates because it minimizes loss of color, ﬂavor, and tex-
tural quality; delays development of sugar spotting, incidence of molds and
yeasts, and insect infestation; and prevents development of syrupiness (due to
conversion of sucrose into reducing sugars) and souring of excessively moist
Khalal dates should be stored at 0 ◦C and 85 to 95% relative humidity to
reduce water loss, delay ripening to the Rutab stage, and maintain their tex-
tural and ﬂavor quality. Packaging in plastic bags or use of plastic liner in the
box helps in minimizing the water loss.
Optimal temperature for Tamar dates is 0 ◦C for 6–12 months storage,
depending on cultivar (semi-soft dates, such as Deglet Nour and Halawi, have
longer storage-life than soft dates, such as Medjhool and Barhi). For longer
storage durations, use temperatures below the highest freezing temperature
of –15.7 ◦C. Dates with 20% moisture or lower can be kept at −18 ◦C for
more than 1 year, at 0 ◦C for one year, at 4 ◦C for 8 months, or at 20 ◦C for
one month; relative humidity should be kept between 65 and 75% in all cases.
Relative humidity is the moisture content (as water vapor) of the atmo-
sphere, expressed as a percentage of the amount of moisture that can be
retained by the atmosphere (moisture holding capacity) at a given temper-
ature and pressure without condensation. The moisture holding capacity of
air increases with temperature. Water loss is directly proportional to the
vapor pressure difference (VPD) between the commodity and its environ-
ment. VPD is inversely related to relative humidity of the air surrounding the
commodity. Relative humidity can inﬂuence water loss, incidence of some
physiological disorders, and fungal growth in dates. Condensation of mois-
ture on the commodity (sweating) over long periods of time is probably more
122 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
important in enhancing decay than is the relative humidity of ambient air.
An appropriate relative humidity range for dates is 65–75%; at higher rela-
tive humidity levels, dates will absorb moisture from the room air unless they
are packaged in moisture-proof containers. Water activity of 0.65 to 0.85 cor-
responds with moisture contents of 15 to 35% in dates. The lower the water
activity, the greater the resistance to molds, yeast, and bacteria that attack
Dates should not be mixed with onions, garlic, potatoes, apples, or other
commodities with strong odors that can be adsorbed by the dates. Exposure
to ammonia or sulfur dioxide can be detrimental to quality of dates (Kader
and Hussein 2009).
Responses to controlled atmospheres
Packaging of Tamar dates in nitrogen (to exclude oxygen) reduces darken-
ing of the fruit and prevents insect infestation. Yellow Khalal Barhi dates can
be stored in 20% carbon dioxide enriched air at 0 ◦C and 90–95% relative
humidity for up to 26 weeks as compared to 7 weeks for air-stored dates (Al-
Redhaiman 2005). The elevated carbon dioxide concentration is fungistatic,
inhibiting growth of fungi, but once the dates are transferred to air, the fun-
gal growth will resume, especially under higher temperatures. Mohsen et al.
(2003) noted that vacuum packaging is a useful technique for reducing dark-
ening of dates during lengthy storage. Mutlak and Mann (1984) reported that
both enzymatic and non-enzymatic browning occurred in dates, increasing
with higher moisture content and higher temperatures and inhibited at low
oxygen potentials. Application of partial vacuum packaging increased the
shelf life for Deglet Nour dates at the Tamar stage stored at <20 ◦C from
3.8 months for simple sealing to 9 months (Achour et al. 1998).
Physical and physiological disorders
Several physiological disorders can appear on dates:
rDarkening: Both enzymatic and non-enzymatic browning occurs in dates
and increase with higher moisture content and higher temperatures. Enzy-
matic browning can be inhibited at low oxygen concentrations and low
rSkin separation (pufﬁness): Skin is dry, hard and brittle, and is separated
from the ﬂesh. This disorder develops during ripening of soft date culti-
vars, which vary in susceptibility. High temperature and high humidity at
a stage before the beginning of ripening may predispose the dates to skin
rSugar spotting (sugaring): This disorder, characterized by light-colored
spots under the skin, results from crystallization of sugars in the ﬂesh of
DISEASE CONTROL STRATEGIES 123
soft date cultivars. Although it does not inﬂuence taste it alters fruit tex-
ture and appearance. Incidence and severity of sugar spotting increase
with storage temperature and time. Storage at recommended tempera-
tures minimizes this disorder, which occurs mainly in cultivars in which
glucose and fructose are the main sugars. Sugaring may be reduced by
gentle heating of the affected dates (Rygg 1975).
Susceptibility of date fruit to postharvest diseases increase after harvest,
during ripening, and over prolonged or inadequate storage as a result of
physiological changes in the fruit, favoring pathogen development. Microbial
spoilage can be caused by yeasts (most important), molds, and bacteria.
Yeast species of Zygosaccharomyces are more tolerant of high sugar con-
tent than others found in dates. Yeast-infected dates develop an alcoholic
odor (become fermented). Acetobacter bacteria may convert the alcohol
into acetic acid (vinegar). Fermentation by yeast also results in souring of
dates due to accumulation of ethanol and/or acetic acid with moisture con-
tent above 25% when kept at temperatures above 20 ◦C and its severity
increases with duration and temperature of storage. Storage at low tempera-
tures reduces incidence and severity of souring.
Fungi (Aspergillus,Alternaria, and Penicillium spp.) may grow on high-
moisture dates, especially when harvested following rain or high humidity
period. Growth of Aspergillus ﬂavus on dates can result in aﬂatoxin contam-
ination that would make them unsafe for human consumption and unmar-
Lactic acid bacteria are present only at the Rutab stage in some varieties
(Tafti and Fooladi 2005).
Disease control strategies
Several strategies can be adopted in order to minimize and control disease
1. Dry the dates to 20% moisture or lower to greatly reduce incidence of
molds and yeasts.
2. Maintain recommended temperature and relative humidity ranges
throughout the handling system. In date-producing countries, it is com-
mon to consume fruit at Khalal and Rutab stages during the harvesting
season. Dates at these stages of maturity have high moisture content and
are prone to rapid deterioration. Therefore, for optimum shelf life, such
fruits should be handled and marketed using cold-chain just like any other
perishable commodities. Kader (2003) recommended maintaining cold-
chain throughout the fruit marketing channels (Figure 5.9).
124 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
Protect the product from the hot sun
Transport quickly to the packinghouse
Minimize delays before cooling
Cool the product as soon as possible
Store the product at its optimum temperature
Practice “first-in-first-out” rotation
Ship to market as soon as possible
TRANSPORT TO MARKET
Use refrigerated loading area
Cool truck before loading
Put insulating plastic strips inside door or
reefer if the truck makes multiple stops
HANDLING AT DESTINATION
Use a refrigerated unloading area
Measure product temperature
Move product quickly to proper storage area
Display at proper temperature range
Avoid delays during transport
HANDLING AT FOODSERVICE OUTLETS
Store product at proper temperature
Monitor product temperature during storage
Use the product as soon as possible
Figure 5.9 Maintaining cold chain for the perishable commodities. Source: Adapted from
3. Avoid temperature ﬂuctuations to prevent moisture condensation on the
dates, which may encourage growth of decay-causing microorganisms.
4. Use adequate sanitation procedures in the packinghouse and storage
rooms to reduce potential sources of microbial contamination.
Insect pests and their control
Insect infestation is one of the primary causes of postharvest losses in
quality and quantity. Several insects can cause serious damage to dates at
different developmental stages (Carpenter and Elmer 1978, Dowson 1982,
Ait-Oubahou and Yahia 1999):
rOligonychus afrasiaticus McGregor and O.pratensis Banks are mites that
cause a disorder known as “Bou Faroua” disorder, which affects fruit at
INSECT PESTS AND THEIR CONTROL 125
the Hababouk stage. The larvae develop around the fruit producing a
white ﬁlament netting, which in turn causes fruits to drop prematurely.
rCoccotrypes dactyliperda (date stone beetle) has the same consequences,
with the fruit dropping at the immature green stage.
rParlatoria blanchardii (date palm scale) attacks the fruit while still green
and forms white ﬁlaments around the fruit, which reduce photosynthesis
and the fruits do not reach maturity.
rEctomyelois ceratoniae Zeller (date carob-moth) is another lepidoteran,
which is widely distributed in different producing areas of dates, and
causes signiﬁcant postharvest losses in stored dates. The moth is common
on dates, pomegranates and carobs.
rBatrachedra amydraula Meyr (lesser date moth), Carpophilus hemipterus
(dried-fruit beetle), C. mutilatus (confused sap beetle), Urophorus humer-
alis (pineapple beetle), and Haptoncus luteolus (pineapple sap beetle), can
cause serious damage to dates on the bunch or after harvest.
rVespa orientalis (Oriental hornet), Cadra ﬁgulilella (raisin moth),
Arenipses sabella (greater date moth), and the Tyrophagus lintneri Osborn
(mushroom mite) can infest stored dates.
rEphestia cautella Walk (ﬁg-moth) is an important postharvest pest in some
growing regions that can attack dates in the orchard, packinghouses or
stores (Ahmed et al. 1994). Dates at the Kimri,Khalal,andRutab stages
are not attacked by this insect, only fruits at the Tamar stage.
rOryzaephilus surinamersis L. (saw-toothed grain beetle) is a serious insect
pest of stored dates in some regions.
Fumigation by methyl bromide or phosphine, ionizing radiation, low and/or
high temperatures, and modiﬁed atmospheres can be used to control insects
in dates (Paull and Armstrong 1994, Yahia 1998, 2009, Yahia and Kader
Methyl bromide (CH3Br) at 30 g/m3(30 ppm) for 12–24 hours at temper-
atures above 16 ◦C is very effective for insect disinfestations (Yahia and
Kader 2011). However, although methyl bromide is very effective in control-
ling stored products insects, its emissions have a deleterious effect on the
atmosphere and it is a tremendous hazard for human health; the Montreal
126 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
Protocol decided to eliminate its production and use by the end of 2015
A potential substitute for methyl bromide is sulfuryl ﬂuoride at 34 g/m3for
24 hours at 20–25 ◦C, which was recently registered by the United States Envi-
ronmental Protection Agency (USEPA), although environmental groups are
campaigning against this compound due to its potential negative effects.
Phosphine (PH3) is an effective fumigant, but treatment takes 3 to 5 days
at 20 ◦C and 60% relative humidity. However, using phosphine as a gas can
shorten the required treatment time to a few hours. Current regulations in
each country should be consulted before these fumigants are used. Fumiga-
tion was found to be more efﬁcient when applied under low pressure. Ahmed
et al. (1982) compared methyl bromide fumigation and irradiation of Zahdi
dates and reported that both techniques are efﬁcient for disinfestation during
the ﬁrst period of storage (25 days), but reinfestation of dates occurred dur-
ing storage leading to detection of live insects. Thus, disinfested dates must
be protected from reinfestation by storage at low temperatures and in insect-
Ionizing radiation at doses below 1 kGy (a level currently approved for use
in fruits and vegetables) has potential for effective insect disinfestations with-
out negative effects on quality of dates (Ahmed 1981, Al-Taweel et al. 1993).
Ahmed et al. (1982) found that a dose of 0.86 kGy was adequate for the
disinfestation of polyethylene-wrapped small date packages, causing com-
plete inhibition of adult emergence of both Ephestia and Oryzaephilus. Al-
Taweel et al. (1990) reported that a dose of 0.44 kGy for 30 minutes was suf-
ﬁcient to disinfest dates and no live insects could be detected after a storage
period of 185 days. Azelmat et al. (2005) found that 0.3 kGy was the mini-
mum needed to prevent damage from feeding and prevent adult emergence,
and 0.45 kGy was required to kill the fourth instar of Plodia interpunctella
(Huber) (Lepidoptera: Pyralidae). Some studies conducted by El-Sayed and
Baeshin (1983), Grecz et al. (1986) and Al-Khahtani et al. (1998) showed that
panellists could not discriminate between control and 0.2 to 6.0 kGy irra-
diated dates. However, Aleid et al. (2013) showed that sensory quality was
affected at >3kGy doses.
Wahbah (2003) reported that microwave radiation at 2540 MHz for 19 to
22 sec was sufﬁcient to cause 50% mortality of the two species O. surinamen-
sis and T. castaneum, respectively, while Al-Azab (2007) indicates that 20 sec
at 2450 MHz were necessary to produce 100% mortality for all E. cautella
stages; with sensitivity being pupae>adults>eggs>larvae.
INSECT PESTS AND THEIR CONTROL 127
Alfaiﬁ et al. (2013) reported the potential for developing continuous and
large-scale radiofrequency treatments (deep 28.4–103.7 cm at 27 MHz) for
postharvest insect control in dried fruits.
Heat treatment of dates at 60–70 ◦C for 2 hours killed 100% of both the ﬁg-
moth and the saw-toothed beetle, but resulted in a shiny appearance or glaz-
ing of the fruit (Hussain 1974). Exposing dates to temperatures of 65–80 ◦C
for 30 min to 4 hours at high humidity controls insects (Yahia 2004); how-
ever, this approach is not always very efﬁcient for controlling insects in dates
with high moisture content because high temperatures for prolonged periods
may cause darkening and the appearance of a dull colour and loss of ﬂavour.
Rafaeli et al. (2006) described an effective, short-duration and inexpensive
method using postharvest heating container. They found that the optimum
temperature regime for maximum escape of beetles from the fruit was 55 ◦C
for 2.5 hours attained at a rate of 1.8 ◦C/min.
Heated air at 50–55 ◦C for 2–4 hours (from the time the fruit temperature
reaches 50 ◦C or higher) is effective for insect disinfestation (Navarro 2006),
but the use of higher temperatures is not recommended because it makes the
color of the dates darker. Forced hot air is recommended to obtain faster and
more uniform heating of the dates. Cooling the dates to the desired storage
temperature (0 ◦C) soon after completion of the heat treatment reduces the
intensity of color darkening. Hussein et al. (1989) reported that boiling water
is more efﬁcient in controlling insect infestation of dates than exposure to hot
air at 70 ◦C. However, very hot water also increases sugar loss that can reach
up to 20%.
Dates are very resistant to low temperature, and thus can signiﬁcantly reduce
insect infestation (Yahia 2004, Yahia and Kader 2011). Temperatures below
13 ◦C will prevent feeding damage and reproduction, and temperatures of
5◦C or lower are effective in controlling different forms of insect (Barreveld
1993). Fig-moth larva could live for 85 days at 2–6 ◦C, but storage at 0 ◦C can
result in total mortality of the larva of the ﬁg-moth and adult of the grain bee-
tle after 15 and 27 days, respectively (Hussain 1974). Thus, packed fumigated
dates could be kept free of infestation at 4 ◦C for as long as 1 year (Hussain
1974). Freezing at –18 ◦C or lower for at least 48 hr (from the time when the
fruit temperature reaches –18 ◦C or lower) is enough to kill all life stages of
stored products insects.
128 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
Modiﬁed atmosphere (MA) and controlled atmosphere (CA)
Packing infested dates in polyethylene bags with 80–90% vacuum resulted in
100% mortality after two days (Hussain 1974). A 4-hour exposure at 2.8%
O2in N2at 26 ◦C resulted in over 80% of the initial nitidulid beetles popula-
tions to emigrate from the infested dried dates (Navarro et al. 1998a, b). Al-
Azab (2007) used a mixture of modiﬁed atmosphere (65% CO2, 15% N2and
20% O2) and found that an exposure for 24 hours at 34 ◦C and 65% relative
humidity cause 100% mortality against the adults of E. cautella. El-Mohandes
(2009) found that 100% mortality was achieved after 36-hour exposure at
CO2concentrations of 75% at 25 ◦C and 55% relative humidity for the adults
of Oryzaephilus surinamensis and Tribolium confusum. Moreover, applica-
tion of CO2at concentrations of 75% with half dose of PH3at 28 ±2◦C and
60 ±5% relative humidity caused 100% mortality, of both tested insects,
after 6 hours of exposure.
Niakousari et al. (2010) exposed contaminated dates with all life stages
(adults, larvae and eggs) of Indian meal moth (Plodia interpunctella) and saw-
tooth grain beetle (Oryzaephilus surinamensis) to gaseous ozone (600, 1200,
2000 and 4000 ppm) for 1–2 hours. Exposing samples to ozone concentrations
of >2000 ppm for 2 hours resulted in complete mortality of larvae and adults.
Ozonation at 4000 ppm caused 80% mortality of eggs but exposure to CO2
prior to ozonation did not increase the mortality.
Some biological methods for the control of the insect pests of stored dates,
such as sterile insect technique, cytoplasmic incompatibility and the use of
parasites, have been tried (Ahmed 1981, Ahmed et al. 1982, 1994), but none
of these methods is used commercially.
“Organic” dates cannot be treated with chemical fumigants and other
treatments such as carbon dioxide, heat treatments or freezing can be used
for insect disinfestation.
Various products can be obtained from dates (Barreveld 1993, Al-Abid et al.
2007a, b). Dates are marketed whole, pitted, cut into small pieces, or mac-
erated (ground or chopped) and can be used in pastries. Whole unpitted or
pitted dates may be marketed loose or pressed (compressed into layers using
mechanical force). Dates products include concentrated Tamar juice (dibis),
liquid sugar, production of alcohol and alcoholic beverages, vinegar, and the
production of single cell protein (Sidhu 2006). Date ﬂour can be obtained
from dry or dried dates. Syrup can be produced from very soft dates (drained
FOOD SAFETY CONSIDERATIONS 129
out) or from low quality dates after hydration and maceration. The syrup
obtained is concentrated to 30/35 ◦Brix then ﬁltered to reach a light brown
colour. Sugar is extracted from dates, and vinegar, alcohol and yeast can also
be produced from dates (Munier 1965). Kimri stage (green) dates may be
used for pickles and chutney. Khalal stage dates may be used for jam or dates-
in-syrup (dibis). Rutab stage dates may be used for jam, butter, date bars, and
date paste. Tamar stage dates may be processed into date bars, date paste, or
date syrup. Date processing by-products and low-quality dates may be used
for sugar extraction or production of sugar alcohols, citric acid, ethanol, vine-
gar, or baker’s yeast.
To remove astringency, dates can be dipped in a solution of 3–4% acetic
acid or in vinegar, or fumigated with acetic acid vapor in a heated container.
Immature dates can also be immersed in hot water for a few minutes or incu-
bated at 32–38 ◦C for a few days, where the fruit softens, become translucent,
and the ﬂavour improves (Ait-Oubahou and Yahia 1999).
Food safety considerations
Safety factors in dates include natural contaminants, such as fungal toxins
(mycotoxins) and bacterial toxins, and heavy metals (cadmium, lead, mer-
cury); environmental pollutants; residues of pesticides; and microbial con-
tamination (Al-Turki and Magid 2004, Yahia 2004). While health authorities
and scientists regard microbial contamination as the number one safety con-
cern, many consumers rank pesticide residues as the most important safety
issue. Unless fertilized with animal and/or human waste or irrigated with
water containing such waste, dates normally should be free of most human
and animal enteric pathogens, unless they have been contaminated if allowed
to fall to the ground. Organic fertilizers, such as chicken manure, should
be sterilized before use in date orchards to avoid the risk of contaminating
dates that contact the soil with Salmonella,Listeria, and other pathogens.
Dates that touch the soil are more likely to be contaminated than those that
do not come in contact with the soil. Strict adherence to “good agricultural
practices (GAPs)” during production, “good hygienic practices (GHPs)” dur-
ing postharvest handling, and “good manufacturing practices (GMPs)” dur-
ing processing are strongly recommended to minimize microbial contamina-
tion. Careful handling and strict observance of proper sanitary measures are
strongly recommended to reduce microbial contamination during all handling
steps (Kader and Hussein 2009).
Kader and Hussain (2009) recommended that date packing and processing
plants establish and consistently implement a Hazard Analysis and Critical
Control Points (HACCP) program to assure safety of their products to the
consumers. Design and implementation of the HACCP system involves seven
essential basic steps, as shown in Figure 5.10. Adopting HACCP program can
check for possible contamination and assure that GMPs are being followed.
130 CH5 HARVESTING AND POSTHARVEST TECHNOLOGY OF DATES
Identify possible food safety hazards
Determine critical control points
Establish preventive measures
Monitor the manufacturing process to detect hazards
Plan corrective actions
Prepare a method to verify that the HACCP plan is working
Document the HACCP system by maintaining records
Figure 5.10 Basic steps of the Hazard Analysis and Critical Control Points (HACCP) system.
Sanitation standard operating procedures (SSOPs) are speciﬁc procedures
that allow the date processing plant to achieve sanitary process control in its
daily operations. These procedures are shown in Figure 5.11.
Proper washing of dates signiﬁcantly reduces the microbial load on their
surfaces. Clean, disinfected water is required in order to minimize the poten-
tial transmission of pathogens from water to dates, from infected to healthy
dates within a single lot, and from one lot to another over time. Waterborne
microorganism, including postharvest plant pathogens and agents of human
illness, can be rapidly acquired and taken up on date surfaces. Natural date
fruit surface contours, natural openings, harvest wounds, and scufﬁng can be
points of entry as well as providing safe harbor for microbes. In these pro-
tected sites, microbes are largely unaffected by common or permitted doses of
postharvest water sanitizing treatments, such as chlorine compounds, ozone,
peroxyacetic acid, and hydrogen peroxide. It is essential therefore, that an
Safety and purity of
the water used in all
Hand washing and
clean toilet facilities
Labeling and storage
of toxic compounds
health, sick workers
not to touch the food
Prevention of cross-
Protection of food
Pest control and
Figure 5.11 Sanitation standard operating procedures (SSOPs) recommended for postharvest
handling of dates. Source: Adapted from Kader and Hussain (2009).
adequate concentration of sanitizer is maintained in water in order to kill
microbes before they attach or become internalized in the dates.
In some countries, standards of microbial quality have been established
with a maximum microbial load allowed in any of the samples tested of 1,000
CFU/g yeasts, 10,000 CFU/g molds, and/or 10 CFU/g Escherichia coli. Such
microbial load testing may be helpful in indicating the efﬁcacy of the sanita-
tion procedures used to prevent microbial contamination.
Many businesses can face challenges, but in particular small-scale produc-
ers and traders in developing countries need support in planning and imple-
menting food safety management programs in line with international require-
ments such as CODEX. The CODEX Standard for dates includes three sizes
based on the number of dates per 500 g: small (>110 dates without or >90
dates with seeds), medium (90–110 dates without or 80–90 dates with seeds),
and large (<90 date without seeds or <80 dates with seeds) (CODEX STAN
Only a small proportion, about 10%, of the world production of dates is han-
dled in global trade due to diverse factors including inadequate handling tech-
niques, and lack of information for small farmers, who are the dominant pro-
ducers. Many topics need to be investigated and improved such as: selection
of adequate cultivars for better quality fruits and smaller tree size; improve-
ments of harvesting methods; ripening procedures; dehydration and hydra-
tion techniques; safe methods for insect and pathogen control; prevention
of toxins and development of adequate detection methods; practical meth-
ods for moisture determination; adequate packaging and storage conditions;
and further biochemical studies on sugar interactions, tissue softening, and
Some of the important means to produce good quality dates and to main-
tain quality after harvest include: selecting the right type of male clones for
pollinating female cultivars, developing adequate date palm mechanization,
especially for pollination and harvesting, adequate use of the cold chain,
packaging and packages, food safety measures, methods of insect control and
prevention of reinfestation during postharvest handling. Use of low temper-
ature during storage and transport is the most important way of maintaining
quality of dates because it minimizes loss of color, ﬂavor, and textural qual-
ity, delays development of sugar spotting, reduces incidence of molds and
yeasts, and insect infestation, and prevents development of syrupiness (due to
conversion of sucrose into reducing sugars) and souring of excessively moist
Achour MI, Hamdi S, Hamdi M. 1998. Effect of the glucose syrup coating on the quality of
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