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DATE PALMS
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DATE PALMS A A A Kwaasi, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia Copyright 2003, Elsevier Science Ltd. All Rights Reserved.
Background 0001
The date palm (Phoenix dactylifera L.) has been known for as long as recorded history. Apart from its importance as a food source for man and animals, all parts of the plant have their use in medicine, pharmacognosy, chemistry, and religion, and in the fishing, horticulture, and construction industries. Like all economic plants, dates are also afflicted by a number of diseases from microbes, insects, and rodents. Dates are one of the few foods that have a high potassium content and, at a certain stage of development, have a low sucrose content. As knowledge in agriculture, medicine, and industry develops, so does the number of new agents that are found to be harmful or useful to man. In the last two decades, there has been a dramatic increase in the number of foods that have been found to be allergenic, and accidental consumption of these foods by susceptible individuals has led to fatalities. Date fruit and pollen are no exception. Results of recent research have revealed that both date pollen and fruit peptides from certain date cultivars can elicit allergic responses in susceptible individuals and share a number of cross-reactive epitopes with some well-known allergens. The beneficial properties of the date are such that its cultivation should be expanded.
History 0002
The date palm has provided inhabitants of the hot dry regions of the world with a highly desirable food and has therefore been thoroughly exploited. The earliest archeological finds dated 5000–6000 bc were from Iran, Egypt, and Pakistan. Remnants of dates have been found in excavations of Neolithic sites dating back 7000–8000 years and in the tombs of Egyptian Pharaohs. The earliest cultivated finds dated around 4000 bc were from Eridu, Lower Mesopotamia in the Bronze Age. Dates are mentioned in Akkadian and Sumerian cuneiform sources (c. 2500 bc) and later. The date palm has historical and religious fame in Judaism, Christianity, and Islam. Date palm fronds are used on Palm Sunday and are thought to have been used in Jesus’ triumphant entry into Jerusalem (Synoptic Gospels, New Testament), and the book of Psalms states that ‘the righteous shall flourish like a
palm tree.’ Date fruits are eaten by most Christians during Christmas and are used in breaking the fast during the Islamic Holy Month of Ramadan. It is mentioned in the Qur’a¯ n (Maryam 19:25–26) in relation to Jesus’ birth, and there are a total of 26 references to dates in this holy book.
Origin and Distribution The palm is presumed to have originated in the Persian Gulf area and in Western India, but its exact origin is difficult to establish. Apart from remnants of some wild dates still present in areas around Jordan and the Iraq–Iran border, all dates known today are fully domesticated. The date was naturalized in Arabia and spread through Northern Africa, Spain, the drier parts of the Nile valley, and around the Euphrates River. From Spain, it was introduced to America, where it is now grown commercially in the warm valleys of Southern California and Arizona. Dates are cultivated throughout the desert regions of the world and grow well between latitudes of 15 and 35 N, from the Canaries and Morocco in the west, to India in the east. It is recorded from all the inner and littoral parts of North Africa, the southern parts of the Balkan Peninsula, and Asia Minor, from Syria, Palestine, Transjordanian, Iraq, Arabia Peninsula, Iran and Baluchistan regions. Dates are grown on family compounds and along streets and highways, and are seen in every conceivable space in the Middle East. The date is cultivated as an ornamental plant in South Europe, where it seldom matures into fruit, except in southern Italy and Spain, and is cultivated in parts of Queensland, Australia.
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Botany The date palm belongs to the Class: Monocotyledoneae, Subclass: Areciae and is a member of the Family Arecaceae (formerly Palmaceae). It is an aborescent, erect, unbranched stem with large petioles that are sheathed at their bases. The tree is characterized by numerous offshoots that are produced at the base of the trunk of young palms. The average mature tree is about 20 m tall, but some may be as high as 30 m. A young, actively bearing date palm, showing offshoots and fruits at the end of the ‘khalaal’ stage is shown in Figure 1. The trunk of the palm is covered with persistent grayish leaf bases. It is surmounted by a handsome array of pinnately divided long leaves and needlesharp fronds. Between 10 and 20 new leaves are
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Figure 1 (see color plate 42) (a) Young actively bearing date palm with offshoots or suckers. (b) Bunches of fruit from the same tree photographed at the end of the ‘khalaal’ stage.
produced annually. Date palm leaves are subtended at their bases by a cylindrical sheath of reticulate mass of tough, fibrous material, together forming a tight protective envelope for the terminal bud. Even though the phyllotaxy of date palm is not always clear, it forms the basis for the identification of some cultivars. The palm produces many long rope-like adventitious roots that arise from the spherical base of the stem, often traversing long distances in search of water and nutrients. In Egypt and Algeria, mycorrhizal association of the root tips with arbuscular fungi of the genera Glomus, Autochthon, Aoufous, and Sclerocystis is common, but Glomus mosseae has been found to be most efficient in helping the date palm maintain water balance. Male and female flowers are borne on different plants (dioecious), but all date plants look alike. Both male and female inflorescences are branched and are completely enclosed during development by sheathing fibrous spathes. The female inflorescence has pendulous branches, and florets (small flowers) are spread out along their entire length. A female flower with branches of male inflorescence inserted and tied, and a male inflorescence with abundant pollen are shown in Figure 2a and 2b, respectively.
A typical female flower (gynoecium) has a small cup-shaped calyx tube formed from three outer perianth segments. It has three inner perianths, which are small and circular, and are closely appressed to the three carpels of the superior apocarpous ovary, each of which is surmounted by a short, hooked stigma. Only one ovary develops into a seed after fertilization. The floral formula of the female flower is: K3C3A0G3. The male palms produce between 30 and 50 inflorescences yearly. Their spathes are narrower and shorter than the female flowers and are covered with a rust-colored powdery coating (See Figure 2b). The inflorescence consists of a short, stiff peduncle with numerous copious branches and white, sweet scented flowers along their length. The male flower has six stamens bearing long flattened anthers with undulate margins and has the floral formula: K3C3A6G0. The center of the androecium bears a (vestigial) small rudimentary ovary. Pollen production is prolific, and typical pollen is light, small, and pale yellow in color, and measures about 8 by 25 mm. Date pollen is distinct and only slightly resembles the pollen of Sabal palmetto and Ginkgo biloba (see scanning electromicrograph of pollen grains in Figure 3).
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Figure 2 (see color plate 43) (a) Female flower with branches of male inflorescence inserted and tied to the female. (b) Opened male inflorescence with abundant pollen.
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Figure 3 Scanning electromicrograph of two pollen grains.
Genetic Diversity 0010
The heterozygous nature of the palm, its dioecious habit and the long period of cultivation, has led to the
establishment of thousands of different date cultivars. In Riyadh (Saudi Arabia) alone, about 100 different cultivars are sold in the local open markets during harvest. A photograph of 18 of these cultivars is
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shown in Figure 4. Results of enzymatic and genetic studies have been carried out on the fruits of several cultivars in Algeria and Iraq, and other studies of isoenzymes in leaves demonstrate that there is a high percentage of polymorphic loci, strong heterozygosity, and genetic diversity among cultivars. Extensive date breeding continues, and reports from the African Centre of Diversity indicate that date cultivars able to withstand such characteristics as alkaline soil, drought, frost, heat, heavy soil, high pH, salt, sand, slope, smog, and water logging have been bred. Furthermore cultivars with such fruit qualities as attractiveness, resistance to spoilage, heavy yield, late or early maturity, richness of flavor, smoothness of skin, and coloration are available in the germplasm repository of USDA, California, USA. Many of the native palms in the Arabian Peninsula and North Africa have originally grown from either volunteer or intentionally nursed seedlings, but in modern date culture, many different cultivars are propagated vegetatively from offshoots or suckers (See Figure 1a). There are hundreds of established varieties or cultivars, and it is estimated that there are 350 cultivars of soft dates in the Basra region of Iraq alone.
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Dates can be categorized into three different groups depending on the type of fruits they produce: soft, semisoft, and dry. Soft dates have a soft fleshy consistency and contain about 60% sugar in the form of glucose and fructose, and this concentration is sufficient to prevent undesired fermentation. They are used fresh or preserved in the form of ‘agwa,’ a pressed mixture of dates. Semisoft dates have a firmer flesh and contain much more sugar than soft dates. Dry dates contain much more sugar than soft and semisoft dates (65 to 70%), and they ripen and dry to a hard consistency while still on the palm tree.
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Ecology The environmental demands of date palms are summed up in the old Arab adage that ‘the date palm needs its feet in running water and its head in the fire of the sky.’ Date palms enjoy high temperatures and can withstand very low temperatures for short periods only. Temperatures below 8 C are harmful. They can tolerate annual precipitation of between 31 and 403 mm and grow well in regions of low humidity and where rainfall is low or nonexistent. Flowering is favored by long, hot, and
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Figure 4 (see color plate 44) Eighteen of the most popular date cultivars sold in Riyadh, Saudi Arabia. Their names are as follows: 1 ¼ Assela, 2 ¼ Labana, 3 ¼ Sabbaka, 4 ¼ Rothana, 5 ¼ Manifi, 6 ¼ Naboot-Ali, 7 ¼ Sefri, 8 ¼ Mabroom, 9 ¼ Roshidia, 10 ¼ Sokary, 11 ¼ Khodri, 12 ¼ Safawi, 13 ¼ Halaw/Helwa, 14 ¼ Hanini, 15 ¼ Barhi, 16 ¼ Juffair, 17 ¼ Qattar, 18 ¼ Seeleg.
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completely dry periods, and an average temperature of 30 C is considered optimal for proper ripening. The plants can tolerate a wide variety of soil types and a fair amount of alkalinity (pH range of 5–8.2) with the only proviso that the soil be well aerated. To bear well, the roots must be in a stratum with less than 1% of alkali salts. Recently, salt-tolerant date cultivars have been bred, and cultivation in halophytic (salty) soils close to the sea has been made possible. Most date palms are grown under carefully controlled irrigations or in oases. Date trees must be pruned to allow new leaves to grow, to prevent rodent and insect infestation, and to facilitate pollination, fruit setting, and harvesting.
Propagation 0014
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Dates can be generally grown from seeds or vegetatively propagated from offshoots, but in recent years, organogenesis has been researched, and the use of plantlets from tissue culture has become popular. Although impractical for the poor peasant farmer, it has the advantage that several plantlets can be produced in a very short time from a small amount of meristematic tissue. Growth of dates from offshoots is, however, the preferred option for the native grower and has almost completely replaced the old fashioned growth from seeds. Adult date palms in their early years produce many offshoots, and these offshoots are removed from the parent plant and transplanted about 9.2 m apart. The young transplanted tree needs protective wrapping or shelter against cold, heat, and wind, and should be watered daily during the first week and once weekly thereafter until the roots have fully developed. In Saudi Arabia, it is common practice for whole mature trees to be dug out and transplanted as a ‘quick fix.’ Growth from seeds is still used in a few areas for pollen production. Date plantations should be irrigated and the soil fertilized. Inter-cropping of date trees with citrus and other fruit plants is common practice, and alfalfa (Medicago sativa) is often grown.
Pollination, Fruit Formation, and Development 0016
It is estimated that one male plant is sufficient to pollinate 50–100 female date trees, and it is common practice to plant 2.4 male plants per hectare. In Saudi Arabia, dates usually flower between February and April, and dates are pollinated during these months. Date pollen can be stored at various temperatures for differing lengths of time without much loss of viability or ability to fertilize female flowers. Dates should
be naturally wind-pollinated, but there is a small contribution from visiting insects and birds. However, the native form of pollination is to insert one to three branches of male inflorescence in the fully exposed female inflorescence (See Figure 2a). In order to effect efficient fertilization and to maximize fruit yield, this method has largely been replaced by hand pollination, in which pollen is placed in porous sacs or dusters and spread as dust on female flowers or by mechanical spraying. A temperature of 35 C is optimal for pollen germination. After successful pollination and fertilization, one of the three ovules of the ovary develops into a one-seeded drupe with a fleshy inner tissue and an outer shiny chitinous skin. The fertilized rudimentary fruit is referred to in Arabic as ‘hababauk.’ Dates take about 200 days to reach maturity. After pollination, the fruit passes through four distinct phases, known in Arabic as ‘kimri,’ ‘khalaal,’ ‘rutab,’ and ‘tamr’ stages. The kimri stage is the time from which the rudimentary seed is formed until it is about 17–19 weeks old. The fruit increases rapidly in size and weight, and in its reducing sugar, acid, and moisture content. This ends the time of botanical maturity, and the fruit turns yellow or red, depending on the cultivar. The khalaal stage is the second stage of development (from 19 to 25 weeks). Weight gain is slow, but sucrose content increases, whereas the moisture content decreases. Tannins start to precipitate, leading to a reduction in astringency, making some varieties palatable and commercially mature at this stage. At the rutab stage, which sets in from around 26 to 28 weeks, there is further moisture loss, and in some varieties, sucrose turns into inverted sugar, and there is browning and skin softening. The moisture content decreases to about 35%, and this is the time during which fresh soft dates are sold. The final stage, tamr, is used only to refer to dates that are left on the palm trees to undergo further ripening, and some dates become self-preserving at this stage.
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World Date Production It is estimated that there are about 90 million date palms in the world. One United Nations Food and Agricultural Organization statistical report names 31 countries as the main date-producing countries. Out of these, only 21 countries export any appreciable amount of their produce. However, 72 countries throughout the world import between 11 and over 500 000 tonnes of dates annually. In the year 2000, the world date production totalled 5.21 million tonnes. Date production figures for each of the 20 leading date-producing countries (except India) are shown in Figure 5.
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Bahrain
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Somalia
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Chad
Qatar
Mauritania
Yemen
Morocco
China
Tunisia
Libya
Oman
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Sudan
Iraq
Algeria
Pakistan
Saudi Arabia
Iran
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Figure 5 World date-production figures (shown as histograms) for the 20 date-producing countries (figures for India not provided).
Pests, Diseases, and Losses 0019
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Dates are afflicted by a number of pests and diseases, which result in substantial losses. Even though new diseases keep emerging, the most important and widespread of these is Bayoud disease, a fungal wilt disease of date trees caused by the fungus Fusarium oxysporium f. sp. albenidis. Plants infected by this and other wilt fungi make way for opportunistic microbes and pests to cause more damage. Some newly emerging diseases are fungal rhizosis (Ceratocystis radicicola) in South Africa and Serenomyces in California, and two new pathogens, Phomopsis phoenicicola and Fusarium equiseti, have been reported from Iraq. The most recently reported diseases (December 2000) are the phytoplasma ‘white tip die-back’ in Northern Sudan and the ‘slow decline’ disease in North Africa. Dates can also be attacked by a range of pests: the scale insect is important in the Dangola District of Northern Sudan, and termite damage is common. Pakistani dates are mainly attacked by borers (Coleoptera spp.) and the red palm weevil, Rhynchosporus ferrugineus. Recently, this weevil has spread to Israel, Jordan, the Palestinian Authority, and Saudi Arabia. An isolated report from Oman implicates the Indian palm weevil (Pseudophilus testaceus) as the cause of some date tree infestations. Ants and locusts are troublesome, and mice and other rodents feed on leaves, tender roots, and fruits. Damage to fruit through direct infestation by fungi results in the production of phytoalexins, and aflatoxin contamination causing severe fungitoxicity during packaging or marketing has been reported in the cultivars Lulu and Naghal. A list of other disease causing agents, pests, and some of the resultant symptoms is given in Table 1.
Table 1 Diseases of the date palm Agent
Symptom/disease
Alternaria spp. Alternaria citri Alternaria stemphylioides Aspergillus niger Auerswaldia palmicola Catenularia fuligenea Ceratostomellara dicicola Colletotrichum gloesporoides Diplodia phoenicum
Leaf spot Brown spot of fruit Fruit rot Calyx end rot Leaf infection Fruit rot Root rot Leaf infection Leaf stalk rot, fruit rot, and shoot blight Black scorch and heart bud rot Inflorescence blight and fruit rot Leaf spot and false smut Black mildew Root knot nematode Decline disease Decline disease Fruit rot Leaf spot Fruit rot Saprophytic contaminant on roots Fruit rot Wood rot
Endoconidiophora paradoxa Fusarium spp. Graphiola phoenicis Meliola furcata Meloidogyne spp. Omphalia pigmentata Omphalia tralucida Penicillium roseum Pestalotia spp. Phomopsis phoenicola Phymatotrichum omnivorum Pleospora herbarum Poria spp.
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Harvesting, Packaging, and Storage Under optimum conditions, dates start fruiting in 3–5 years of planting an offshoot and reach full maturity in 12 years. Dates are usually harvested from July to September, and the estimated yield of dates per bunch is about 5–15 kg. After harvest, dates are packed or transported loose to the market, packing, or processing plants. The majority of techniques that are applied by commercial growers to prevent infestation and spoilage are fumigation, heat treatment, chilled storage, and irradiation. The most
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popular fumigant is hydrogen phosphide. Methyl bromide was also commonly used, but, owing to its toxicity to man and animals, it has been banned in most parts of the world. Heat treatment is an effective method for disease and spoilage control, because a 100% mortality can be achieved at all stages of the life cycle of some insects. Refrigeration at 4 C is used to prolong the storage life of dates, making it possible to keep dates of 20% moisture content for a year without any changes in appearance and taste. Analyses have confirmed that glucose, fructose, sucrose, and protein contents are the same in irradiated as in nonirradiated dates. Combined treatments seem to be the best choice for overall pest and microbial control.
Quality Control Procedures in Date Production 0023
In organized date-handling companies, dates are sorted and cleaned to achieve homogeneity. Different date cultivars ripen and mature at different times and are therefore picked at different times. Dates are often delivered to the processing or packing plants as a mixture, where they are sorted, cleaned, and graded into cull dates, first-, second- and third-grade dates. Cull dates are used for animal feed, whereas first- and second-class dates are packaged, and third-grade dates are used for commercial date products. After sorting and grading, dates are dry-cleaned by moving them over damp towelling, on mechanical shakers, or on rotating cylinders. They are then air-dried and, depending on their use, are sent for further processing, such as dehydration, hydration, glazing, coating, and pitting.
General Uses 0024
There is an old Arab adage that ‘there are as many uses for dates as there are days in the year’. The date palm is primarily cultivated for its fruit, which is eaten fresh, dry, or variously processed. It is a high-energy food, containing mainly sugar. In areas where dates are a staple food, the variety of date products includes date honey, date sugar, and date wine, which are made from fresh date fruit juice. A date drink called ‘nabidh’ is prepared by soaking mashed up dates in water for one night. The traditional use of date syrup in some Islamic countries used to be mainly on a specific occasion: it would be poured on fermented dough (asseda) and eaten on the occasion of the Prophet’s birthday. Early records indicate that date syrup has been an overland export material between the Middle East and China for many years, and it is widely
used on breads, in softening and preserving dates in jars, and in home-made confectionery. In recent years, date syrup has been used as a base for beverages and bakery products, and in icecreams. Even though attempts to use it in the preparation of soft drinks have proved difficult, a carbonated date syrup-based soft drink of Swiss origin (Tamra) is marketed in Saudi Arabia. Dates are customarily cooked and packaged as candies for local consumption or for export. Date palm flour is made from the pith of the tree, young leaves are cooked as vegetables, and the terminal bud and palm heart are eaten as salad. Oil is made from the seeds (pits or kernel), which is mainly used for making soap. It was believed in ancient Egypt that when a woman of childbearing age ate two date seeds, she would be childless for several years. The kernel can be ground and used as animal feed. Crystallized inverted sugar from dates is sold in certain date-producing countries, and the seeds can be strung and used as beads. In medieval times, the palm was believed to prevent sunstroke, avert lightning, cure fevers, and drive away mice and fleas. Several other uses have been recorded in folk medicine, and it has been observed that there is a very low incidence of cancers in the Bedouins, attributable to their heavy dependence on dates as a staple food. Mats, hats, and baskets are woven from date leaves, and the fibers are used for ropes and thread and for rigging boats. In traditional Arab villages, the leaves are used for roofing, and the midribs are used for fencing. The leaves are used as manure, and shredded palm leaves serve as a good substrate for the growth of tomatoes and cucumber. The sap and inflorescence (mostly from senile plants) after fermentation are a good source of palm wine or toddy (alcoholic content 5%), which is either drunk in its natural state or made into liquor. Arrak is an example of an alcoholic beverage distilled from dates. The wood from the trunk is used as firewood, timber for doors, beams, camel saddles, roofing rafters, cords, ropes, baskets, crates, and furniture.
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Chemistry of the Different Parts of the Date Palm Dates, like many plants, are a source of different chemicals. One unexpected compound in date tissue is serotonin, with levels of up to 850 mg per 100 g. Date leaves contain coumarin, luteolin-7-glucoside, luteolin-7-rutinoside, and glycosylapigenin. The main minerals in the leaves and petioles are nitrogen, phosphorus, potassium, and ash. Date pollen mainly contains cholesterol, rutin, carotenoids, and estrone, and is known to exert
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gonadotrophic activity in rats. Pollen mixed with honey is eaten as an aphrodisiac. The main hemicellulose in date pollen is made up of arabinose (46%), galactose (25%), xylose (18%), rhamnose (9%), and 2% uronic acid. Dry date fruit pulp has an average moisture content of 22.5% with an energy yield of 1151 kJ. It contains 1.9–2% protein, 0.45% lipids, 73.5% carbohydrates, and 7.5% fiber. Its mineral content, in decreasing order, is: potassium > phosphorus > magnesium > calcium > sodium > selenium > iron, but it also contains trace amounts of zinc, copper, and magnesium. Workers in some parts of the world have reported similar chemical contents, but in India, a small amount of arsenic has been detected. Other constituents in the pulp are leucanthocyanins, pipecolic acid, tannins as well as baikiain, and the sarocarp has been shown to contain cholesterol, campesterol, stigmasterol, b-sitosterol, and isofucosterol. Date fruit pulp contains some vitamins: vitamin A, folate, and niacin are in appreciable quantities, but riboflavin, palmitic acid, vitamins B6, and E, and thiamine are present in trace quantities. (See Vitamins: Overview.) The lipid content of date pulp can be as low as 0.2%. It is higher in monounsaturated 16:1 and 18:1 fatty acids than the polyunsaturated fatty acids of 18:2 and 18:3 species. The low protein content of dates is reflected in its poor amino acid content: apart from glutamic acid, aspartic acid, proline, and glycine, which are present at 213, 126, 106, and 95 mg per 100 g, respectively, of date pulp, it contains only trace amounts of most of the other essential amino acids. Some workers have reported high amounts of arginine, but generally, tryptophan, isoleucine and lysine are absent. Date pits (seeds or kernel) make up between 6 and 12% of the total weight of date fruit and have a moisture content of 5–10%. Other constituents of pits are 7% proteins, 10% oils, 10–20% crude fiber, 55–65% carbohydrates and 1–2% ash. Date pits are relatively high in fatty acids, oleic/linoleic acids, (mostly c. 44–52%) and contain appreciable amounts of tannic acid, 17–24% lauric acid, about 10% each of myristic acid, palmitic acids, and linoleic acid, and trace amounts of stearate, capric, and caprylic acids. At the tamr stage, the pit contains cholesterol, estrones, polysaccharide A (with d-mannose and d-galactose at a ratio of 10:1), polysaccharide B, and xylose. (See Carbohydrates: Classification and Properties; Fatty Acids: Properties.) Of the essential amino acids, glutamic acid, aspartic acid, and arginine account for about half of the total proteins in date pits, whereas tryptophan is the most limiting, followed by isoleucine and lysine. The oil extracted from date pits has some uses and has
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the following physico-chemical properties. It has a specific gravity of 0.9207 (at 15 C), a refractive index of 1.4580 (at 40 C), an iodine value of 50– 55, and a saponification value of 205–210. Date pits also contain a few minerals. These are, in decreasing order: potassium > phosphorus > magnesium > calcium > sodium. The only important microelements detectable in date seeds are iron, manganese, zinc, and copper. From a general human nutrition point of view, date pits are unimportant but have one asset, a high digestibility. The only known human food is the Bedouin dish called ‘canua,’ which is made from roasted date seeds. However, date seeds are an invaluable source as a main or supplementary diet for animals. It has been suggested that date seed meal can replace barley in chick rations. Ground date seeds can replace 20–75% of ruminant rations, and 75.5% of a wheat bran–barley mixture can be used for feeding carp. Traditionally, date pits are used in feeding pigs, sheep, and camels, for fattening cattle, and for blending in chicken feed. (See Amino Acids: Properties and Occurrence.)
Commercially Available Date-Derived Products The only time that dates are used for derived products is when there is a temporary surplus, when dates are damaged, or when dates are undersize or unattractive. Date products can be classified under: sweets, preserves, condiments, breakfast foods, and desserts. Dates are used to a larger extent in the bakery and confectionery industry than they are credited for, probably due to poor or cryptic labeling of such products. It is estimated that over 500 biscuits, cakes, cookies, cereals, toffees, chocolates, breads, and other products that contain date products or are predominantly made from dates can be found in supermarkets, health food stores, and other outlets around the world. One date merchant alone in Saudi Arabia stocks over 110 pastries, and each of these items contains dates or is decorated with dates or date syrup. Figure 6 shows a basket, woven from date fiber, filled with a decoration of 110 different confectionery products, dates from 14 different dry date cultivars, a background of semisoft brown dates, date leaves, and bunches of mature dates. Dates are a common supplement in a number of sauces, chutneys, jams, sauces, preserves, and cereals in supermarkets throughout the world. Major worldwide commercial food manufacturers such as Shields Dessert Products, Sun Country, Quaker, Kellogg’s, Pillsbury, Betty Crocker, Bakery Wagon, IBSO, Edfina, HP, Crosse & Blackwells, and Shaws use dates in a number of their products. Cereals containing dates
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Figure 6 (see color plate 45) Basket, woven from date fiber and filled with 110 different confectionery products made from dates and date syrup (and dates from 14 different dry date cultivars). The background shows semisoft brown dates, date leaves, and bunches of mature dates.
are mostly combined with oatmeal, raisins, walnuts, sultana, and almonds, and products with these combinations have energy yields of between 116 kcal (485 kJ) and 360 kcal (1527 kJ) per 100 g. Date juice, presscake, and date syrup are the most common commercially derived date products. The raw juice is the main product, and presscake is the byproduct. Date syrup is obtained after evaporation of date juice. Analysis of date syrup from Iraq and Libya reveals an average of 76% total solids, 69–72% inverted sugar, 0.9–3.2% sucrose, 0.9–1.2% proteins, 0.06–0.17% tannin, 0.25–0.60% total pectin (as impure calcium pectate), 0.46–0.76 citric acid, and 1.6–1.8% ash, and a pH of between 4.14 and 4.66. A number of products like date spread, date syrup, caramel, and liquid sugar are made from date juice concentrates. The fruit pulp is used in semisolid infant foods mixed with whey and skimmed milk, and date liquid sugar is used by some manufacturers as a replacement for sucrose in the white layer in cakes. Some low-calorie sweeteners in soft drinks are prepared from dates.
Fermentation Products 0037
Dates should theoretically be used as a main nutrient for microbial conversion to produce a range of useful fermentation products. Unfortunately, unlike beet or cane sugar, date fruit is not a typical sugar crop because most date cultivars contain high levels of
inverted sugar. At the consumable stage, most of the sucrose has been inverted by the enzyme invertase into glucose and fructose. In addition, dates are expensive and have a high tannin content that restricts its use as a cheap fermentation product. (See Fermented Foods: Origins and Applications.) Dates have, however, been used in the production of a number of products. Lipids have been successfully produced using the fat-producing fungi Penicillium lilacinum, P. soppi, and Aspergillus nidulans. Aspergillus niger has been used for the production of citric acid from date syrup and molasses, and fodder yeast has been produced from Iraqi dates. Postextraction waste material is used as a cultural medium for Candida utilis and Trichoderma viride, and date seeds are also used to produce citric acid from Candida lipolytica. Dates were used as a reinforcement and flavoring agent in beer-making in ancient Egypt, and references to date wine can be found in early history. What is not clear in these old records is whether the wine referred to was fermented or not. Dates are generally not suitable for wine-making because they lack natural acidity, flavor, and astringency. However, in Iraq, good-quality light-colored dry wines have been produced from zahdi dates, and a darker sweeter wine is fermented from the date syrup, dibis. Pure alcohol can be produced from the fermented mother liquor by distillation, and a so-called sherry can be obtained from the transitional product between wine and the
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distilled pure alcohol. Vinegar (vin-aigre, from the French meaning ‘sour wine’) or acetic acid can also be made from date wines that turn sour. A number of organic acids can be produced either directly or indirectly from date sugars. Single-cell protein from date products has been the focus of investigations for a number of years, and promising results have indicated that bakers’ yeast can be produced on date extracts in the same way as it is traditionally produced on molasses.
Allergenicity of Date Fruit and Pollen 0041
Numerous epidemiological studies have reported a steady and significant increase in the world-wide prevalence of allergic diseases in the last two decades. In Saudi Arabia and most of the Middle Eastern countries, it is common knowledge amongst the inhabitants that date pollen causes asthma and allergic rhinitis, and some of the fruits, on ingestion, can cause itching of the mouth and throat. In spite of these observations, there have been no published references on date palm allergens. Results of pioneering studies carried out at the King Faisal Specialist Hospital and Research Centre in Riyadh, Saudi Arabia on the allergenicity of date pollen and fruits in Saudi Arabia have confirmed that date pollen and fruits of some cultivars are allergenic. In the allergic population studied, 25% were allergic to the pollen and 13% to the fruits. These results have been confirmed by workers in Spain, Israel, Kuwait, and France, and cases of anaphylactic shock have been reported. Six pollen components of 12, 14, 27–30, 37–40, 57, and 65–67 kDa, three fruit components of 14.3, 27–33, and 54–58 kDa have been found to be the major date allergens. These allergens have been found to share cross-reactive epitopes with a number of foods that have been implicated in the oral allergy syndrome. These allergenic peptides are novel and are unique to some date pollen and fruits cultivars only. However, amino acid sequencing has indicated that date allergens albeit novel, have similar isoelectric points (pIs) to, and share sequence homologies with, known allergenic structures, namely profilins, wound-induced proteins, cross-reactive carbohydrate determinants, pathogenicity-related, acidic class III chitinase, and endochitinase proteins.
General Comments and Future Prospects 0042
Clearly, the date palm is an important plant, and date-derived products used in foods are more common the world over than had been known. It is also clear from the production, export, and import data that there is an imbalance in production,
1739
consumption, and export. The need to increase date production to meet increasing demand is indicated. Date fruit cultivars that have a high inverted sugar content can be developed further to yield more fructose at their inverted stage. Since dates have a high potassium content, and some hypertensive patients who take diuretics need potassium supplements in their diet, cultivars that have a high potassium, high fructose, and low glucose content can be bred to help with the dietary management of diabetes mellitus. Even though the palm has been known for many years to be one of the most disease-resistant and hardy plants, it appears from the range of infectious agents listed here that the date palm is under threat from new and old pathogens. More effort should be concentrated on breeding high-yielding, disease-resistant, and hypoallergenic varieties. Phytopathological research needs to be focused on, and all aspects of date production improved and diversified. See also: Aflatoxins; Allergens; Amino Acids: Properties and Occurrence; Arsenic: Properties and Determination; Dehydration; Dietary Fiber: Properties and Sources; Fermented Foods: Origins and Applications; Hemicelluloses; Insect Pests: Insects and Related Pests; Irradiation of Foods: Basic Principles; Jams and Preserves: Methods of Manufacture; Syrups
Further Reading Al-Ogaidi HKH, Al-Janabi SM and Al-Shakhli IM (1987) Production of carbonated beverage using date juice. Effect of gelatine, tannin and pH on clarification of date juice (Arabic). Date Palm Journal 5: 2. Al-Rawi N, Narkakis P and Beuer DH (1967) Amino acid composition of Iraqi dates. Journal of the Science of Food and Agriculture 18: 1–2. Barett HC (1973) Date breeding and improvement in North America. Fruit Varieties Journal 27: 50–55. Duke JA (1978) The quest for tolerant germplasm. In: ASA Special Symposium 32, Crop Tolerance to Suboptimal Land Conditions, pp. 1–61. Madison, WI: American Society of Agronomy. Khaliel AS and Abou HAN (1985) Formation of vesicular– arbuscular mycorrhizae in Phoenix dactylifera, cultivated in Qasim region, Saudi Arabia. Pakistan Journal of Botany 17: 267–270. Knight R Jr (1980) Origin and world importance of tropical and subtropical fruit crops. In: Nagy S and Shaw PE (eds) Tropical and Subtropical Fruits, pp. 1–120. Westport, CT: AVI. Krueger RR (1995) Mystique of the date palm links old and new worlds. Diversity 11: 128–129. Kwaasi AAA, Harfi HA, Parhar RS et al. (2000) Cultivarspecific IgE-epitopes in date (Phoenix dactylifera L.) fruit allergy. International Archive of Allergy Immunology 123: 137–144.
1740 DEHYDRATION Kwaasi AAA, Parhar RS, Tipirneni P, Harfi H and AlSedairy ST (1993) Major allergens of date palm (Phoenix dactylifera L.) pollen. Identification of IgE-binding components by ELISA and immunoblot analysis. Allergy 48: 511–518. Kwaasi AAA, Harfi HA, Parhar RS et al. (2002) Crossreactivities between Date Palm (Phoenix dactylifera L.) peptides and foods implicated in the oral allergy syndrome (OAS). Allergy 57(6): 508–518. Riedel HR (1986) Dates, where they come from and how they can be used in the confectionery industry (Ge). Kakao und Zucker 38: 12. Sachde AG, Al-Kiasy AM and Norris RAK (1981) A study of the possibility of producing quality wines from
some commercial varieties of Iraqi dates. Mesopotamia Journal of Agriculture 16(1): 483. Salim N (1976) Fructose Increase from Dates and its Separation. Report PDRC-TB-5/76. Palm and Dates Research Centre, Baghdad, Iraq. Report PDRC-TB-5/76. Samarawira I (1983) Date palm (Phœnix dactylifera). Potential source of refined sugar. Economic Botany 37: 181–186. Shurafa El- MY, Ahmed HS and Abou-Naji SE (1982) Organic and inorganic constituents of date palm pit (seed) in Libya. Date Palm Journal 1(2): 537. Tisserat BH (1979) Tissue culture of date palm. Journal of Heredity 70: 221–222.
Degradation See Spoilage: Chemical and Enzymatic Spoilage; Bacterial Spoilage; Fungi in Food – An Overview; Molds in Spoilage; Yeasts in Spoilage; Storage Stability: Mechanisms of Degradation; Parameters Affecting Storage Stability; Shelf-life Testing
DEHYDRATION S P Allison, University Hospital, Nottingham, UK Copyright 2003, Elsevier Science Ltd. All Rights Reserved.
Definition 0001
Dehydration strictly means lack of water but has come to be used more colloquially to mean salt and water depletion and, even more loosely, to mean a deficit in body fluid of any kind. It is unfortunate that such loose terminology leads to loose thinking, imprecise diagnosis, and, in some cases, inappropriate treatment. In contrast, the terms ‘water depletion,’ ‘salt and water depletion,’ and ‘plasma volume deficit,’ have more precise diagnostic meaning and imply the appropriate treatment for their correction. Pure water depletion is in fact rare. The most obvious example is diabetes insipidus, caused by a lack of antidiuretic hormone. In contrast, salt and water depletion, or desalination, is extremely common. A prime example is that caused by diarrheal diseases, which kills millions of children throughout the world each year.
Physiology 0002
The loss and gain of fluid by the body to and from its surroundings are normally small compared with the enormous daily flux between the different
compartments within the body. Assuming the maximal concentrating ability of healthy kidneys, the volume of urine required to excrete waste products may be as little as 500 ml, although it is safer to allow 1–1.5 l. Insensible loss by evaporation from the lungs may be 500 ml, and from the skin surface 400 ml, although this may be greatly increased in hot climates or during fever, owing to sweating. The amount lost from the gastrointestinal tract as feces is usually as little as 100 ml, but in the presence of diarrheal disease, this may increase enormously. Thus, the minimal daily input of fluid to maintain balance in a healthy adult in a temperate climate is approximately 1500 ml, although 2 l provides a safer margin. In warmer climates this requirement is increased considerably. (See Renal Function and Disorders: Kidney: Structure and Function.) The distribution of body fluids in an adult between different compartments is shown in Figure 1. Total body water is approximately 60% of the bodyweight (more in small children, less in the obese). The intracellular fluid (ICF) is just over 40% of body weight and extracellular fluid (ECF) just under 20% of bodyweight; 25% of the ECF is within the intravascular space, i.e., plasma; the remaining 75% is termed the ‘interstitial fluid’ and surrounds the cells. The integrity of these body fluid compartments is maintained by the properties of their separating membranes (e.g.,
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DATE PALMS A A A Kwaasi, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia Copyright 2003, Elsevier Science Ltd. All Rights Reserved.
Background 0001
The date palm (Phoenix dactylifera L.) has been known for as long as recorded history. Apart from its importance as a food source for man and animals, all parts of the plant have their use in medicine, pharmacognosy, chemistry, and religion, and in the fishing, horticulture, and construction industries. Like all economic plants, dates are also afflicted by a number of diseases from microbes, insects, and rodents. Dates are one of the few foods that have a high potassium content and, at a certain stage of development, have a low sucrose content. As knowledge in agriculture, medicine, and industry develops, so does the number of new agents that are found to be harmful or useful to man. In the last two decades, there has been a dramatic increase in the number of foods that have been found to be allergenic, and accidental consumption of these foods by susceptible individuals has led to fatalities. Date fruit and pollen are no exception. Results of recent research have revealed that both date pollen and fruit peptides from certain date cultivars can elicit allergic responses in susceptible individuals and share a number of cross-reactive epitopes with some well-known allergens. The beneficial properties of the date are such that its cultivation should be expanded.
History 0002
The date palm has provided inhabitants of the hot dry regions of the world with a highly desirable food and has therefore been thoroughly exploited. The earliest archeological finds dated 5000–6000 bc were from Iran, Egypt, and Pakistan. Remnants of dates have been found in excavations of Neolithic sites dating back 7000–8000 years and in the tombs of Egyptian Pharaohs. The earliest cultivated finds dated around 4000 bc were from Eridu, Lower Mesopotamia in the Bronze Age. Dates are mentioned in Akkadian and Sumerian cuneiform sources (c. 2500 bc) and later. The date palm has historical and religious fame in Judaism, Christianity, and Islam. Date palm fronds are used on Palm Sunday and are thought to have been used in Jesus’ triumphant entry into Jerusalem (Synoptic Gospels, New Testament), and the book of Psalms states that ‘the righteous shall flourish like a
palm tree.’ Date fruits are eaten by most Christians during Christmas and are used in breaking the fast during the Islamic Holy Month of Ramadan. It is mentioned in the Qur’a¯ n (Maryam 19:25–26) in relation to Jesus’ birth, and there are a total of 26 references to dates in this holy book.
Origin and Distribution The palm is presumed to have originated in the Persian Gulf area and in Western India, but its exact origin is difficult to establish. Apart from remnants of some wild dates still present in areas around Jordan and the Iraq–Iran border, all dates known today are fully domesticated. The date was naturalized in Arabia and spread through Northern Africa, Spain, the drier parts of the Nile valley, and around the Euphrates River. From Spain, it was introduced to America, where it is now grown commercially in the warm valleys of Southern California and Arizona. Dates are cultivated throughout the desert regions of the world and grow well between latitudes of 15 and 35 N, from the Canaries and Morocco in the west, to India in the east. It is recorded from all the inner and littoral parts of North Africa, the southern parts of the Balkan Peninsula, and Asia Minor, from Syria, Palestine, Transjordanian, Iraq, Arabia Peninsula, Iran and Baluchistan regions. Dates are grown on family compounds and along streets and highways, and are seen in every conceivable space in the Middle East. The date is cultivated as an ornamental plant in South Europe, where it seldom matures into fruit, except in southern Italy and Spain, and is cultivated in parts of Queensland, Australia.
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Botany The date palm belongs to the Class: Monocotyledoneae, Subclass: Areciae and is a member of the Family Arecaceae (formerly Palmaceae). It is an aborescent, erect, unbranched stem with large petioles that are sheathed at their bases. The tree is characterized by numerous offshoots that are produced at the base of the trunk of young palms. The average mature tree is about 20 m tall, but some may be as high as 30 m. A young, actively bearing date palm, showing offshoots and fruits at the end of the ‘khalaal’ stage is shown in Figure 1. The trunk of the palm is covered with persistent grayish leaf bases. It is surmounted by a handsome array of pinnately divided long leaves and needlesharp fronds. Between 10 and 20 new leaves are
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(b)
Figure 1 (see color plate 42) (a) Young actively bearing date palm with offshoots or suckers. (b) Bunches of fruit from the same tree photographed at the end of the ‘khalaal’ stage.
produced annually. Date palm leaves are subtended at their bases by a cylindrical sheath of reticulate mass of tough, fibrous material, together forming a tight protective envelope for the terminal bud. Even though the phyllotaxy of date palm is not always clear, it forms the basis for the identification of some cultivars. The palm produces many long rope-like adventitious roots that arise from the spherical base of the stem, often traversing long distances in search of water and nutrients. In Egypt and Algeria, mycorrhizal association of the root tips with arbuscular fungi of the genera Glomus, Autochthon, Aoufous, and Sclerocystis is common, but Glomus mosseae has been found to be most efficient in helping the date palm maintain water balance. Male and female flowers are borne on different plants (dioecious), but all date plants look alike. Both male and female inflorescences are branched and are completely enclosed during development by sheathing fibrous spathes. The female inflorescence has pendulous branches, and florets (small flowers) are spread out along their entire length. A female flower with branches of male inflorescence inserted and tied, and a male inflorescence with abundant pollen are shown in Figure 2a and 2b, respectively.
A typical female flower (gynoecium) has a small cup-shaped calyx tube formed from three outer perianth segments. It has three inner perianths, which are small and circular, and are closely appressed to the three carpels of the superior apocarpous ovary, each of which is surmounted by a short, hooked stigma. Only one ovary develops into a seed after fertilization. The floral formula of the female flower is: K3C3A0G3. The male palms produce between 30 and 50 inflorescences yearly. Their spathes are narrower and shorter than the female flowers and are covered with a rust-colored powdery coating (See Figure 2b). The inflorescence consists of a short, stiff peduncle with numerous copious branches and white, sweet scented flowers along their length. The male flower has six stamens bearing long flattened anthers with undulate margins and has the floral formula: K3C3A6G0. The center of the androecium bears a (vestigial) small rudimentary ovary. Pollen production is prolific, and typical pollen is light, small, and pale yellow in color, and measures about 8 by 25 mm. Date pollen is distinct and only slightly resembles the pollen of Sabal palmetto and Ginkgo biloba (see scanning electromicrograph of pollen grains in Figure 3).
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(b)
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Figure 2 (see color plate 43) (a) Female flower with branches of male inflorescence inserted and tied to the female. (b) Opened male inflorescence with abundant pollen.
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Figure 3 Scanning electromicrograph of two pollen grains.
Genetic Diversity 0010
The heterozygous nature of the palm, its dioecious habit and the long period of cultivation, has led to the
establishment of thousands of different date cultivars. In Riyadh (Saudi Arabia) alone, about 100 different cultivars are sold in the local open markets during harvest. A photograph of 18 of these cultivars is
DATE PALMS
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fig0004
shown in Figure 4. Results of enzymatic and genetic studies have been carried out on the fruits of several cultivars in Algeria and Iraq, and other studies of isoenzymes in leaves demonstrate that there is a high percentage of polymorphic loci, strong heterozygosity, and genetic diversity among cultivars. Extensive date breeding continues, and reports from the African Centre of Diversity indicate that date cultivars able to withstand such characteristics as alkaline soil, drought, frost, heat, heavy soil, high pH, salt, sand, slope, smog, and water logging have been bred. Furthermore cultivars with such fruit qualities as attractiveness, resistance to spoilage, heavy yield, late or early maturity, richness of flavor, smoothness of skin, and coloration are available in the germplasm repository of USDA, California, USA. Many of the native palms in the Arabian Peninsula and North Africa have originally grown from either volunteer or intentionally nursed seedlings, but in modern date culture, many different cultivars are propagated vegetatively from offshoots or suckers (See Figure 1a). There are hundreds of established varieties or cultivars, and it is estimated that there are 350 cultivars of soft dates in the Basra region of Iraq alone.
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Dates can be categorized into three different groups depending on the type of fruits they produce: soft, semisoft, and dry. Soft dates have a soft fleshy consistency and contain about 60% sugar in the form of glucose and fructose, and this concentration is sufficient to prevent undesired fermentation. They are used fresh or preserved in the form of ‘agwa,’ a pressed mixture of dates. Semisoft dates have a firmer flesh and contain much more sugar than soft dates. Dry dates contain much more sugar than soft and semisoft dates (65 to 70%), and they ripen and dry to a hard consistency while still on the palm tree.
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Ecology The environmental demands of date palms are summed up in the old Arab adage that ‘the date palm needs its feet in running water and its head in the fire of the sky.’ Date palms enjoy high temperatures and can withstand very low temperatures for short periods only. Temperatures below 8 C are harmful. They can tolerate annual precipitation of between 31 and 403 mm and grow well in regions of low humidity and where rainfall is low or nonexistent. Flowering is favored by long, hot, and
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Figure 4 (see color plate 44) Eighteen of the most popular date cultivars sold in Riyadh, Saudi Arabia. Their names are as follows: 1 ¼ Assela, 2 ¼ Labana, 3 ¼ Sabbaka, 4 ¼ Rothana, 5 ¼ Manifi, 6 ¼ Naboot-Ali, 7 ¼ Sefri, 8 ¼ Mabroom, 9 ¼ Roshidia, 10 ¼ Sokary, 11 ¼ Khodri, 12 ¼ Safawi, 13 ¼ Halaw/Helwa, 14 ¼ Hanini, 15 ¼ Barhi, 16 ¼ Juffair, 17 ¼ Qattar, 18 ¼ Seeleg.
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completely dry periods, and an average temperature of 30 C is considered optimal for proper ripening. The plants can tolerate a wide variety of soil types and a fair amount of alkalinity (pH range of 5–8.2) with the only proviso that the soil be well aerated. To bear well, the roots must be in a stratum with less than 1% of alkali salts. Recently, salt-tolerant date cultivars have been bred, and cultivation in halophytic (salty) soils close to the sea has been made possible. Most date palms are grown under carefully controlled irrigations or in oases. Date trees must be pruned to allow new leaves to grow, to prevent rodent and insect infestation, and to facilitate pollination, fruit setting, and harvesting.
Propagation 0014
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Dates can be generally grown from seeds or vegetatively propagated from offshoots, but in recent years, organogenesis has been researched, and the use of plantlets from tissue culture has become popular. Although impractical for the poor peasant farmer, it has the advantage that several plantlets can be produced in a very short time from a small amount of meristematic tissue. Growth of dates from offshoots is, however, the preferred option for the native grower and has almost completely replaced the old fashioned growth from seeds. Adult date palms in their early years produce many offshoots, and these offshoots are removed from the parent plant and transplanted about 9.2 m apart. The young transplanted tree needs protective wrapping or shelter against cold, heat, and wind, and should be watered daily during the first week and once weekly thereafter until the roots have fully developed. In Saudi Arabia, it is common practice for whole mature trees to be dug out and transplanted as a ‘quick fix.’ Growth from seeds is still used in a few areas for pollen production. Date plantations should be irrigated and the soil fertilized. Inter-cropping of date trees with citrus and other fruit plants is common practice, and alfalfa (Medicago sativa) is often grown.
Pollination, Fruit Formation, and Development 0016
It is estimated that one male plant is sufficient to pollinate 50–100 female date trees, and it is common practice to plant 2.4 male plants per hectare. In Saudi Arabia, dates usually flower between February and April, and dates are pollinated during these months. Date pollen can be stored at various temperatures for differing lengths of time without much loss of viability or ability to fertilize female flowers. Dates should
be naturally wind-pollinated, but there is a small contribution from visiting insects and birds. However, the native form of pollination is to insert one to three branches of male inflorescence in the fully exposed female inflorescence (See Figure 2a). In order to effect efficient fertilization and to maximize fruit yield, this method has largely been replaced by hand pollination, in which pollen is placed in porous sacs or dusters and spread as dust on female flowers or by mechanical spraying. A temperature of 35 C is optimal for pollen germination. After successful pollination and fertilization, one of the three ovules of the ovary develops into a one-seeded drupe with a fleshy inner tissue and an outer shiny chitinous skin. The fertilized rudimentary fruit is referred to in Arabic as ‘hababauk.’ Dates take about 200 days to reach maturity. After pollination, the fruit passes through four distinct phases, known in Arabic as ‘kimri,’ ‘khalaal,’ ‘rutab,’ and ‘tamr’ stages. The kimri stage is the time from which the rudimentary seed is formed until it is about 17–19 weeks old. The fruit increases rapidly in size and weight, and in its reducing sugar, acid, and moisture content. This ends the time of botanical maturity, and the fruit turns yellow or red, depending on the cultivar. The khalaal stage is the second stage of development (from 19 to 25 weeks). Weight gain is slow, but sucrose content increases, whereas the moisture content decreases. Tannins start to precipitate, leading to a reduction in astringency, making some varieties palatable and commercially mature at this stage. At the rutab stage, which sets in from around 26 to 28 weeks, there is further moisture loss, and in some varieties, sucrose turns into inverted sugar, and there is browning and skin softening. The moisture content decreases to about 35%, and this is the time during which fresh soft dates are sold. The final stage, tamr, is used only to refer to dates that are left on the palm trees to undergo further ripening, and some dates become self-preserving at this stage.
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World Date Production It is estimated that there are about 90 million date palms in the world. One United Nations Food and Agricultural Organization statistical report names 31 countries as the main date-producing countries. Out of these, only 21 countries export any appreciable amount of their produce. However, 72 countries throughout the world import between 11 and over 500 000 tonnes of dates annually. In the year 2000, the world date production totalled 5.21 million tonnes. Date production figures for each of the 20 leading date-producing countries (except India) are shown in Figure 5.
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Somalia
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Morocco
China
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Libya
Oman
UAE
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Iraq
Algeria
Pakistan
Saudi Arabia
Iran
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Figure 5 World date-production figures (shown as histograms) for the 20 date-producing countries (figures for India not provided).
Pests, Diseases, and Losses 0019
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Dates are afflicted by a number of pests and diseases, which result in substantial losses. Even though new diseases keep emerging, the most important and widespread of these is Bayoud disease, a fungal wilt disease of date trees caused by the fungus Fusarium oxysporium f. sp. albenidis. Plants infected by this and other wilt fungi make way for opportunistic microbes and pests to cause more damage. Some newly emerging diseases are fungal rhizosis (Ceratocystis radicicola) in South Africa and Serenomyces in California, and two new pathogens, Phomopsis phoenicicola and Fusarium equiseti, have been reported from Iraq. The most recently reported diseases (December 2000) are the phytoplasma ‘white tip die-back’ in Northern Sudan and the ‘slow decline’ disease in North Africa. Dates can also be attacked by a range of pests: the scale insect is important in the Dangola District of Northern Sudan, and termite damage is common. Pakistani dates are mainly attacked by borers (Coleoptera spp.) and the red palm weevil, Rhynchosporus ferrugineus. Recently, this weevil has spread to Israel, Jordan, the Palestinian Authority, and Saudi Arabia. An isolated report from Oman implicates the Indian palm weevil (Pseudophilus testaceus) as the cause of some date tree infestations. Ants and locusts are troublesome, and mice and other rodents feed on leaves, tender roots, and fruits. Damage to fruit through direct infestation by fungi results in the production of phytoalexins, and aflatoxin contamination causing severe fungitoxicity during packaging or marketing has been reported in the cultivars Lulu and Naghal. A list of other disease causing agents, pests, and some of the resultant symptoms is given in Table 1.
Table 1 Diseases of the date palm Agent
Symptom/disease
Alternaria spp. Alternaria citri Alternaria stemphylioides Aspergillus niger Auerswaldia palmicola Catenularia fuligenea Ceratostomellara dicicola Colletotrichum gloesporoides Diplodia phoenicum
Leaf spot Brown spot of fruit Fruit rot Calyx end rot Leaf infection Fruit rot Root rot Leaf infection Leaf stalk rot, fruit rot, and shoot blight Black scorch and heart bud rot Inflorescence blight and fruit rot Leaf spot and false smut Black mildew Root knot nematode Decline disease Decline disease Fruit rot Leaf spot Fruit rot Saprophytic contaminant on roots Fruit rot Wood rot
Endoconidiophora paradoxa Fusarium spp. Graphiola phoenicis Meliola furcata Meloidogyne spp. Omphalia pigmentata Omphalia tralucida Penicillium roseum Pestalotia spp. Phomopsis phoenicola Phymatotrichum omnivorum Pleospora herbarum Poria spp.
tbl0001
Harvesting, Packaging, and Storage Under optimum conditions, dates start fruiting in 3–5 years of planting an offshoot and reach full maturity in 12 years. Dates are usually harvested from July to September, and the estimated yield of dates per bunch is about 5–15 kg. After harvest, dates are packed or transported loose to the market, packing, or processing plants. The majority of techniques that are applied by commercial growers to prevent infestation and spoilage are fumigation, heat treatment, chilled storage, and irradiation. The most
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popular fumigant is hydrogen phosphide. Methyl bromide was also commonly used, but, owing to its toxicity to man and animals, it has been banned in most parts of the world. Heat treatment is an effective method for disease and spoilage control, because a 100% mortality can be achieved at all stages of the life cycle of some insects. Refrigeration at 4 C is used to prolong the storage life of dates, making it possible to keep dates of 20% moisture content for a year without any changes in appearance and taste. Analyses have confirmed that glucose, fructose, sucrose, and protein contents are the same in irradiated as in nonirradiated dates. Combined treatments seem to be the best choice for overall pest and microbial control.
Quality Control Procedures in Date Production 0023
In organized date-handling companies, dates are sorted and cleaned to achieve homogeneity. Different date cultivars ripen and mature at different times and are therefore picked at different times. Dates are often delivered to the processing or packing plants as a mixture, where they are sorted, cleaned, and graded into cull dates, first-, second- and third-grade dates. Cull dates are used for animal feed, whereas first- and second-class dates are packaged, and third-grade dates are used for commercial date products. After sorting and grading, dates are dry-cleaned by moving them over damp towelling, on mechanical shakers, or on rotating cylinders. They are then air-dried and, depending on their use, are sent for further processing, such as dehydration, hydration, glazing, coating, and pitting.
General Uses 0024
There is an old Arab adage that ‘there are as many uses for dates as there are days in the year’. The date palm is primarily cultivated for its fruit, which is eaten fresh, dry, or variously processed. It is a high-energy food, containing mainly sugar. In areas where dates are a staple food, the variety of date products includes date honey, date sugar, and date wine, which are made from fresh date fruit juice. A date drink called ‘nabidh’ is prepared by soaking mashed up dates in water for one night. The traditional use of date syrup in some Islamic countries used to be mainly on a specific occasion: it would be poured on fermented dough (asseda) and eaten on the occasion of the Prophet’s birthday. Early records indicate that date syrup has been an overland export material between the Middle East and China for many years, and it is widely
used on breads, in softening and preserving dates in jars, and in home-made confectionery. In recent years, date syrup has been used as a base for beverages and bakery products, and in icecreams. Even though attempts to use it in the preparation of soft drinks have proved difficult, a carbonated date syrup-based soft drink of Swiss origin (Tamra) is marketed in Saudi Arabia. Dates are customarily cooked and packaged as candies for local consumption or for export. Date palm flour is made from the pith of the tree, young leaves are cooked as vegetables, and the terminal bud and palm heart are eaten as salad. Oil is made from the seeds (pits or kernel), which is mainly used for making soap. It was believed in ancient Egypt that when a woman of childbearing age ate two date seeds, she would be childless for several years. The kernel can be ground and used as animal feed. Crystallized inverted sugar from dates is sold in certain date-producing countries, and the seeds can be strung and used as beads. In medieval times, the palm was believed to prevent sunstroke, avert lightning, cure fevers, and drive away mice and fleas. Several other uses have been recorded in folk medicine, and it has been observed that there is a very low incidence of cancers in the Bedouins, attributable to their heavy dependence on dates as a staple food. Mats, hats, and baskets are woven from date leaves, and the fibers are used for ropes and thread and for rigging boats. In traditional Arab villages, the leaves are used for roofing, and the midribs are used for fencing. The leaves are used as manure, and shredded palm leaves serve as a good substrate for the growth of tomatoes and cucumber. The sap and inflorescence (mostly from senile plants) after fermentation are a good source of palm wine or toddy (alcoholic content 5%), which is either drunk in its natural state or made into liquor. Arrak is an example of an alcoholic beverage distilled from dates. The wood from the trunk is used as firewood, timber for doors, beams, camel saddles, roofing rafters, cords, ropes, baskets, crates, and furniture.
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Chemistry of the Different Parts of the Date Palm Dates, like many plants, are a source of different chemicals. One unexpected compound in date tissue is serotonin, with levels of up to 850 mg per 100 g. Date leaves contain coumarin, luteolin-7-glucoside, luteolin-7-rutinoside, and glycosylapigenin. The main minerals in the leaves and petioles are nitrogen, phosphorus, potassium, and ash. Date pollen mainly contains cholesterol, rutin, carotenoids, and estrone, and is known to exert
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gonadotrophic activity in rats. Pollen mixed with honey is eaten as an aphrodisiac. The main hemicellulose in date pollen is made up of arabinose (46%), galactose (25%), xylose (18%), rhamnose (9%), and 2% uronic acid. Dry date fruit pulp has an average moisture content of 22.5% with an energy yield of 1151 kJ. It contains 1.9–2% protein, 0.45% lipids, 73.5% carbohydrates, and 7.5% fiber. Its mineral content, in decreasing order, is: potassium > phosphorus > magnesium > calcium > sodium > selenium > iron, but it also contains trace amounts of zinc, copper, and magnesium. Workers in some parts of the world have reported similar chemical contents, but in India, a small amount of arsenic has been detected. Other constituents in the pulp are leucanthocyanins, pipecolic acid, tannins as well as baikiain, and the sarocarp has been shown to contain cholesterol, campesterol, stigmasterol, b-sitosterol, and isofucosterol. Date fruit pulp contains some vitamins: vitamin A, folate, and niacin are in appreciable quantities, but riboflavin, palmitic acid, vitamins B6, and E, and thiamine are present in trace quantities. (See Vitamins: Overview.) The lipid content of date pulp can be as low as 0.2%. It is higher in monounsaturated 16:1 and 18:1 fatty acids than the polyunsaturated fatty acids of 18:2 and 18:3 species. The low protein content of dates is reflected in its poor amino acid content: apart from glutamic acid, aspartic acid, proline, and glycine, which are present at 213, 126, 106, and 95 mg per 100 g, respectively, of date pulp, it contains only trace amounts of most of the other essential amino acids. Some workers have reported high amounts of arginine, but generally, tryptophan, isoleucine and lysine are absent. Date pits (seeds or kernel) make up between 6 and 12% of the total weight of date fruit and have a moisture content of 5–10%. Other constituents of pits are 7% proteins, 10% oils, 10–20% crude fiber, 55–65% carbohydrates and 1–2% ash. Date pits are relatively high in fatty acids, oleic/linoleic acids, (mostly c. 44–52%) and contain appreciable amounts of tannic acid, 17–24% lauric acid, about 10% each of myristic acid, palmitic acids, and linoleic acid, and trace amounts of stearate, capric, and caprylic acids. At the tamr stage, the pit contains cholesterol, estrones, polysaccharide A (with d-mannose and d-galactose at a ratio of 10:1), polysaccharide B, and xylose. (See Carbohydrates: Classification and Properties; Fatty Acids: Properties.) Of the essential amino acids, glutamic acid, aspartic acid, and arginine account for about half of the total proteins in date pits, whereas tryptophan is the most limiting, followed by isoleucine and lysine. The oil extracted from date pits has some uses and has
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the following physico-chemical properties. It has a specific gravity of 0.9207 (at 15 C), a refractive index of 1.4580 (at 40 C), an iodine value of 50– 55, and a saponification value of 205–210. Date pits also contain a few minerals. These are, in decreasing order: potassium > phosphorus > magnesium > calcium > sodium. The only important microelements detectable in date seeds are iron, manganese, zinc, and copper. From a general human nutrition point of view, date pits are unimportant but have one asset, a high digestibility. The only known human food is the Bedouin dish called ‘canua,’ which is made from roasted date seeds. However, date seeds are an invaluable source as a main or supplementary diet for animals. It has been suggested that date seed meal can replace barley in chick rations. Ground date seeds can replace 20–75% of ruminant rations, and 75.5% of a wheat bran–barley mixture can be used for feeding carp. Traditionally, date pits are used in feeding pigs, sheep, and camels, for fattening cattle, and for blending in chicken feed. (See Amino Acids: Properties and Occurrence.)
Commercially Available Date-Derived Products The only time that dates are used for derived products is when there is a temporary surplus, when dates are damaged, or when dates are undersize or unattractive. Date products can be classified under: sweets, preserves, condiments, breakfast foods, and desserts. Dates are used to a larger extent in the bakery and confectionery industry than they are credited for, probably due to poor or cryptic labeling of such products. It is estimated that over 500 biscuits, cakes, cookies, cereals, toffees, chocolates, breads, and other products that contain date products or are predominantly made from dates can be found in supermarkets, health food stores, and other outlets around the world. One date merchant alone in Saudi Arabia stocks over 110 pastries, and each of these items contains dates or is decorated with dates or date syrup. Figure 6 shows a basket, woven from date fiber, filled with a decoration of 110 different confectionery products, dates from 14 different dry date cultivars, a background of semisoft brown dates, date leaves, and bunches of mature dates. Dates are a common supplement in a number of sauces, chutneys, jams, sauces, preserves, and cereals in supermarkets throughout the world. Major worldwide commercial food manufacturers such as Shields Dessert Products, Sun Country, Quaker, Kellogg’s, Pillsbury, Betty Crocker, Bakery Wagon, IBSO, Edfina, HP, Crosse & Blackwells, and Shaws use dates in a number of their products. Cereals containing dates
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Figure 6 (see color plate 45) Basket, woven from date fiber and filled with 110 different confectionery products made from dates and date syrup (and dates from 14 different dry date cultivars). The background shows semisoft brown dates, date leaves, and bunches of mature dates.
are mostly combined with oatmeal, raisins, walnuts, sultana, and almonds, and products with these combinations have energy yields of between 116 kcal (485 kJ) and 360 kcal (1527 kJ) per 100 g. Date juice, presscake, and date syrup are the most common commercially derived date products. The raw juice is the main product, and presscake is the byproduct. Date syrup is obtained after evaporation of date juice. Analysis of date syrup from Iraq and Libya reveals an average of 76% total solids, 69–72% inverted sugar, 0.9–3.2% sucrose, 0.9–1.2% proteins, 0.06–0.17% tannin, 0.25–0.60% total pectin (as impure calcium pectate), 0.46–0.76 citric acid, and 1.6–1.8% ash, and a pH of between 4.14 and 4.66. A number of products like date spread, date syrup, caramel, and liquid sugar are made from date juice concentrates. The fruit pulp is used in semisolid infant foods mixed with whey and skimmed milk, and date liquid sugar is used by some manufacturers as a replacement for sucrose in the white layer in cakes. Some low-calorie sweeteners in soft drinks are prepared from dates.
Fermentation Products 0037
Dates should theoretically be used as a main nutrient for microbial conversion to produce a range of useful fermentation products. Unfortunately, unlike beet or cane sugar, date fruit is not a typical sugar crop because most date cultivars contain high levels of
inverted sugar. At the consumable stage, most of the sucrose has been inverted by the enzyme invertase into glucose and fructose. In addition, dates are expensive and have a high tannin content that restricts its use as a cheap fermentation product. (See Fermented Foods: Origins and Applications.) Dates have, however, been used in the production of a number of products. Lipids have been successfully produced using the fat-producing fungi Penicillium lilacinum, P. soppi, and Aspergillus nidulans. Aspergillus niger has been used for the production of citric acid from date syrup and molasses, and fodder yeast has been produced from Iraqi dates. Postextraction waste material is used as a cultural medium for Candida utilis and Trichoderma viride, and date seeds are also used to produce citric acid from Candida lipolytica. Dates were used as a reinforcement and flavoring agent in beer-making in ancient Egypt, and references to date wine can be found in early history. What is not clear in these old records is whether the wine referred to was fermented or not. Dates are generally not suitable for wine-making because they lack natural acidity, flavor, and astringency. However, in Iraq, good-quality light-colored dry wines have been produced from zahdi dates, and a darker sweeter wine is fermented from the date syrup, dibis. Pure alcohol can be produced from the fermented mother liquor by distillation, and a so-called sherry can be obtained from the transitional product between wine and the
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distilled pure alcohol. Vinegar (vin-aigre, from the French meaning ‘sour wine’) or acetic acid can also be made from date wines that turn sour. A number of organic acids can be produced either directly or indirectly from date sugars. Single-cell protein from date products has been the focus of investigations for a number of years, and promising results have indicated that bakers’ yeast can be produced on date extracts in the same way as it is traditionally produced on molasses.
Allergenicity of Date Fruit and Pollen 0041
Numerous epidemiological studies have reported a steady and significant increase in the world-wide prevalence of allergic diseases in the last two decades. In Saudi Arabia and most of the Middle Eastern countries, it is common knowledge amongst the inhabitants that date pollen causes asthma and allergic rhinitis, and some of the fruits, on ingestion, can cause itching of the mouth and throat. In spite of these observations, there have been no published references on date palm allergens. Results of pioneering studies carried out at the King Faisal Specialist Hospital and Research Centre in Riyadh, Saudi Arabia on the allergenicity of date pollen and fruits in Saudi Arabia have confirmed that date pollen and fruits of some cultivars are allergenic. In the allergic population studied, 25% were allergic to the pollen and 13% to the fruits. These results have been confirmed by workers in Spain, Israel, Kuwait, and France, and cases of anaphylactic shock have been reported. Six pollen components of 12, 14, 27–30, 37–40, 57, and 65–67 kDa, three fruit components of 14.3, 27–33, and 54–58 kDa have been found to be the major date allergens. These allergens have been found to share cross-reactive epitopes with a number of foods that have been implicated in the oral allergy syndrome. These allergenic peptides are novel and are unique to some date pollen and fruits cultivars only. However, amino acid sequencing has indicated that date allergens albeit novel, have similar isoelectric points (pIs) to, and share sequence homologies with, known allergenic structures, namely profilins, wound-induced proteins, cross-reactive carbohydrate determinants, pathogenicity-related, acidic class III chitinase, and endochitinase proteins.
General Comments and Future Prospects 0042
Clearly, the date palm is an important plant, and date-derived products used in foods are more common the world over than had been known. It is also clear from the production, export, and import data that there is an imbalance in production,
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consumption, and export. The need to increase date production to meet increasing demand is indicated. Date fruit cultivars that have a high inverted sugar content can be developed further to yield more fructose at their inverted stage. Since dates have a high potassium content, and some hypertensive patients who take diuretics need potassium supplements in their diet, cultivars that have a high potassium, high fructose, and low glucose content can be bred to help with the dietary management of diabetes mellitus. Even though the palm has been known for many years to be one of the most disease-resistant and hardy plants, it appears from the range of infectious agents listed here that the date palm is under threat from new and old pathogens. More effort should be concentrated on breeding high-yielding, disease-resistant, and hypoallergenic varieties. Phytopathological research needs to be focused on, and all aspects of date production improved and diversified. See also: Aflatoxins; Allergens; Amino Acids: Properties and Occurrence; Arsenic: Properties and Determination; Dehydration; Dietary Fiber: Properties and Sources; Fermented Foods: Origins and Applications; Hemicelluloses; Insect Pests: Insects and Related Pests; Irradiation of Foods: Basic Principles; Jams and Preserves: Methods of Manufacture; Syrups
Further Reading Al-Ogaidi HKH, Al-Janabi SM and Al-Shakhli IM (1987) Production of carbonated beverage using date juice. Effect of gelatine, tannin and pH on clarification of date juice (Arabic). Date Palm Journal 5: 2. Al-Rawi N, Narkakis P and Beuer DH (1967) Amino acid composition of Iraqi dates. Journal of the Science of Food and Agriculture 18: 1–2. Barett HC (1973) Date breeding and improvement in North America. Fruit Varieties Journal 27: 50–55. Duke JA (1978) The quest for tolerant germplasm. In: ASA Special Symposium 32, Crop Tolerance to Suboptimal Land Conditions, pp. 1–61. Madison, WI: American Society of Agronomy. Khaliel AS and Abou HAN (1985) Formation of vesicular– arbuscular mycorrhizae in Phoenix dactylifera, cultivated in Qasim region, Saudi Arabia. Pakistan Journal of Botany 17: 267–270. Knight R Jr (1980) Origin and world importance of tropical and subtropical fruit crops. In: Nagy S and Shaw PE (eds) Tropical and Subtropical Fruits, pp. 1–120. Westport, CT: AVI. Krueger RR (1995) Mystique of the date palm links old and new worlds. Diversity 11: 128–129. Kwaasi AAA, Harfi HA, Parhar RS et al. (2000) Cultivarspecific IgE-epitopes in date (Phoenix dactylifera L.) fruit allergy. International Archive of Allergy Immunology 123: 137–144.
1740 DEHYDRATION Kwaasi AAA, Parhar RS, Tipirneni P, Harfi H and AlSedairy ST (1993) Major allergens of date palm (Phoenix dactylifera L.) pollen. Identification of IgE-binding components by ELISA and immunoblot analysis. Allergy 48: 511–518. Kwaasi AAA, Harfi HA, Parhar RS et al. (2002) Crossreactivities between Date Palm (Phoenix dactylifera L.) peptides and foods implicated in the oral allergy syndrome (OAS). Allergy 57(6): 508–518. Riedel HR (1986) Dates, where they come from and how they can be used in the confectionery industry (Ge). Kakao und Zucker 38: 12. Sachde AG, Al-Kiasy AM and Norris RAK (1981) A study of the possibility of producing quality wines from
some commercial varieties of Iraqi dates. Mesopotamia Journal of Agriculture 16(1): 483. Salim N (1976) Fructose Increase from Dates and its Separation. Report PDRC-TB-5/76. Palm and Dates Research Centre, Baghdad, Iraq. Report PDRC-TB-5/76. Samarawira I (1983) Date palm (Phœnix dactylifera). Potential source of refined sugar. Economic Botany 37: 181–186. Shurafa El- MY, Ahmed HS and Abou-Naji SE (1982) Organic and inorganic constituents of date palm pit (seed) in Libya. Date Palm Journal 1(2): 537. Tisserat BH (1979) Tissue culture of date palm. Journal of Heredity 70: 221–222.
Degradation See Spoilage: Chemical and Enzymatic Spoilage; Bacterial Spoilage; Fungi in Food – An Overview; Molds in Spoilage; Yeasts in Spoilage; Storage Stability: Mechanisms of Degradation; Parameters Affecting Storage Stability; Shelf-life Testing
DEHYDRATION S P Allison, University Hospital, Nottingham, UK Copyright 2003, Elsevier Science Ltd. All Rights Reserved.
Definition 0001
Dehydration strictly means lack of water but has come to be used more colloquially to mean salt and water depletion and, even more loosely, to mean a deficit in body fluid of any kind. It is unfortunate that such loose terminology leads to loose thinking, imprecise diagnosis, and, in some cases, inappropriate treatment. In contrast, the terms ‘water depletion,’ ‘salt and water depletion,’ and ‘plasma volume deficit,’ have more precise diagnostic meaning and imply the appropriate treatment for their correction. Pure water depletion is in fact rare. The most obvious example is diabetes insipidus, caused by a lack of antidiuretic hormone. In contrast, salt and water depletion, or desalination, is extremely common. A prime example is that caused by diarrheal diseases, which kills millions of children throughout the world each year.
Physiology 0002
The loss and gain of fluid by the body to and from its surroundings are normally small compared with the enormous daily flux between the different
compartments within the body. Assuming the maximal concentrating ability of healthy kidneys, the volume of urine required to excrete waste products may be as little as 500 ml, although it is safer to allow 1–1.5 l. Insensible loss by evaporation from the lungs may be 500 ml, and from the skin surface 400 ml, although this may be greatly increased in hot climates or during fever, owing to sweating. The amount lost from the gastrointestinal tract as feces is usually as little as 100 ml, but in the presence of diarrheal disease, this may increase enormously. Thus, the minimal daily input of fluid to maintain balance in a healthy adult in a temperate climate is approximately 1500 ml, although 2 l provides a safer margin. In warmer climates this requirement is increased considerably. (See Renal Function and Disorders: Kidney: Structure and Function.) The distribution of body fluids in an adult between different compartments is shown in Figure 1. Total body water is approximately 60% of the bodyweight (more in small children, less in the obese). The intracellular fluid (ICF) is just over 40% of body weight and extracellular fluid (ECF) just under 20% of bodyweight; 25% of the ECF is within the intravascular space, i.e., plasma; the remaining 75% is termed the ‘interstitial fluid’ and surrounds the cells. The integrity of these body fluid compartments is maintained by the properties of their separating membranes (e.g.,
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