Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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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



Cis

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 treat-

ments 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 process-

ing, 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 bever-

ages 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 consump-

tion or for export.

0025Date palm flour is made from the pith of the tree,

young leaves are cooked as vegetables, and the ter-

minal 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 light-

ning, cure fevers, and drive away mice and fleas.

Several other uses have been recorded in folk medi-

cine, 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.

0026Mats, 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 bev-

erage 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.

Chemistry of the Different Parts of the

Date Palm

0027Dates, 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.

0028Date pollen mainly contains cholesterol, rutin,

carotenoids, and estrone, and is known to exert

1736 DATE PALMS

gonadotrophic activity in rats. Pollen mixed with

honey is eaten as an aphrodisiac. The main hemicel-

lulose in date pollen is made up of arabinose (46%),

galactose (25%), xylose (18%), rhamnose (9%), and

2% uronic acid.

0029 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 > cal-

cium > 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 constitu-

ents in the pulp are leucanthocyanins, pipecolic acid,

tannins as well as baikiain, and the sarocarp has been

shown to contain cholesterol, campesterol, stigmas-

terol, b-sitosterol, and isofucosterol. Date fruit pulp

contains some vitamins: vitamin A, folate, and niacin

are in appreciable quantities, but riboflavin, palmitic

acid, vitamins B

, and E, and thiamine are present in

trace quantities. (See Vitamins: Overview.)

0030 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 gly-

cine, 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.

0031 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.)

0032 Of the essential amino acids, glutamic acid, aspar-

tic 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

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 decreas-

ing 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

0033The 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, pre-

serves, condiments, breakfast foods, and desserts.

Dates are used to a larger extent in the bakery and

confectionery industry than they are credited for, prob-

ably due to poor or cryptic labeling of such products. It

is estimated that over 500 biscuits, cakes, cookies,

cereals, toffees, chocolates, breads, and other prod-

ucts 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.

0034Figure 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.

0035Dates are a common supplement in a number of

sauces, chutneys, jams, sauces, preserves, and cereals

in supermarkets throughout the world. Major world-

wide 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

DATE PALMS 1737

are mostly combined with oatmeal, raisins, walnuts,

sultana, and almonds, and products with these combin-

ations have energy yields of between 116 kcal (485 kJ)

and 360 kcal (1527 kJ) per 100 g.

0036 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 ex-

pensive and have a high tannin content that restricts

its use as a cheap fermentation product. (See Fer-

mented Foods: Origins and Applications.)

0038Dates have, however, been used in the production

of a number of products. Lipids have been success-

fully produced using the fat-producing fungi Penicil-

lium 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.

0039Dates 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 pro-

duced 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

fig0006 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.

1738 DATE PALMS

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.

0040 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 in-

habitants 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 ref-

erences on date palm allergens. Results of pioneering

studies carried out at the King Faisal Specialist Hos-

pital 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 popula-

tion 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,

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 fruc-

tose 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-re-

sistant, and hypoallergenic varieties. Phytopathologi-

cal 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, culti-

vated 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. West-

port, 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) Cultivar-

specific IgE-epitopes in date (Phoenix dactylifera L.)

fruit allergy. International Archive of Allergy Immun-

ology 123: 137–144.

DATE PALMS 1739

Kwaasi AAA, Parhar RS, Tipirneni P, Harfi H and Al-

Sedairy ST (1993) Major allergens of date palm (Phoe-

nix 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) Cross-

reactivities between Date Palm (Phoenix dactylifera L.)

peptides and foods implicated in the oral allergy syn-

drome (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 Separ-

ation. 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

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 treat-

ment. 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 mil-

lions 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 max-

imal 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 dis-

ease, this may increase enormously. Thus, the min-

imal 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 consid-

erably. (See Renal Function and Disorders: Kidney:

Structure and Function.)

0003The 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 intra-

cellular fluid (ICF) is just over 40% of body weight

and extracellular fluid (ECF) just under 20% of body-

weight; 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 integ-

rity of these body fluid compartments is maintained

by the properties of their separating membranes (e.g.,

1740 DEHYDRATION

the cell membrane with its sodium pump, and the

capillary membrane and its pore size) and their

osmotic or oncotic content (e.g., sodium ions Na

for ECF; potassium ions, K

, for ICF; albumin for

plasma). Not only is the external fluid balance

important, but also changes in fluid compartments,

where shifts may be large. For example, the rate of

exchange of albumin between the intravascular and

interstitial spaces is normally 10 times its rate of

synthesis. Fluid deficits may also have different effects

on each compartment. In an average adult, a deficit of

2 l of pure water reduces the total body water evenly

by 2 l (and, incidentally, the weight by 2 kg) with a

1400 ml reduction in ICF, a 600-ml reduction in ECF

fluid, and a 150-ml reduction in plasma volume.

However, a loss of 2 l of salt and water, at a concen-

tration of 140 mmol Na

per liter, reduces the total

body water by 2 l and the weight by 2 kg but causes a

selective loss of 2 l from the ECF, with a consequent

reduction in plasma volume of nearly 500 ml. The

clinical problems presented by these two situations

are of an entirely different order. (See Potassium:

Physiology; Sodium: Physiology; Water: Physiology.)

0004 To understand the problems of fluid deficit, it is

also necessary to consider the large daily volume of

secretions, particularly those into the gastrointestinal

tract (Table 1). Under normal circumstances, these

are almost entirely reabsorbed, with a minimal daily

loss of 100 ml in the feces. With gastrointestinal

disease, e.g., vomiting, diarrhea or fistula, large

volumes of water and electrolytes may be lost to the

outside or, in the case of intestinal obstruction or ileus,

pooled in the gut and lost to the functional compart-

ments. In an adult, during a normal day, 8000 ml of

fluid enter the small bowel; 500 ml as saliva, 1200 ml

as gastric fluid, 600 ml as bile, 1200 ml as pancreatic

juice, 2000 ml as small bowel secretion, and the re-

mainder as ingested fluid. All but 1.5 l is reabsorbed in

the small intestine, and a further 1.4 l is reabsorbed

in the colon with much of the remaining sodium chlor-

ide. Approximate electrolyte content of gastrointest-

inal secretions is shown in Table 1.

Diagnosis and Monitoring

0005In common with most diagnoses, that of dehydration

depends mainly on the history and examination. The

history, combined with a knowledge of the natural

history of the presenting condition, provides the main

clues to the presence of salt and water depletion, the

likely progress of the condition and the necessary

treatment.

0006The physical signs are helpful, but none are patho-

gnomonic. The facies and eyes appear sunken, but this

is also seen in cachexia. The mouth and tongue are dry,

but this can also be caused by mouth breathing. The

skin turgor, assessed by pinching up a fold of skin and

observing its recoil, is diminished with salt depletion

but also in old age, cachexia, and extreme cold. A

marked fall in blood pressure between the lying and

sitting or standing positions is also characteristic of

salt and water depletion, as is tachycardia. A low

output of concentrated urine, associated with a rise

in blood urea owing to prerenal failure, is also seen.

0007Other biochemical indices are less useful in diagno-

sis. The plasma sodium concentration gives no clue to

the total body sodium content, unless water balance is

also known. It merely reflects the relative proportion

Cell membrane

ICF = 40% bodyweight

Interstitial

fluid

140 mmol

4 mmol

0 mmol

151 mmol

Capillary membrane

Plasma

albumin

40 g l

−1

RBCs

TBW ~ 60% bodyweight

EcF ~ 20% bodyweight

fig0001 Figure 1 Diagrammatic representation of body fluid compart-

ments and concentrations of sodium ions (Na

), potassium ions

) and albumin. TBW, total body water; ICF, intracellular fluid;

ECF, extracellular fluid; RBCs, red blood cells. Reproduced from

Dehydration, Encyclopaedia of Food Science, Food Technology and

Nutrition, Macrae R, Robinson RK and Sadler MJ (eds), 1993,

Academic Press.

tbl0001Table 1 Approximate electrolyte content of gastrointestinal

secretions

Secretion Sodium (Na

)

(mmoll

1

)

Potassium (K

)

(mmoll

1

)

Chloride (Cl



)

(mmoll

1

)

Saliva 44 20

Gastric 70–120 10 100

Small intestine 110–120 5–10 105

Bile 140 5 100

Pancreas 140 5 75

Diarrhea

Cholera (adult) 120 15 90

Cholera (child) 100 27 90

Nonspecific

(child)

56 25 55

DEHYDRATION 1741

of sodium and water in the extracellular space. Thus,

with pure water lack, the plasma sodium concentra-

tion increases. With a mixed deficit of sodium and

water, the plasma sodium reflects the relative propor-

tion of the two that are lost.

0008 Progress is first monitored by observing the im-

provement in the appearance of the patient; guard

against fluid overload by watching for edema, a

raised jugular venous pressure, or pulmonary edema.

A fluid balance chart is valuable, but water balance is

best measured by changes in weight, which should be

monitored at least daily. Plasma sodium concentra-

tion changes can then be interpreted in the light of

water balance.

Conditions Associated with Water and

Salt Depletion

Diarrhea

0009 Worldwide, diarrhea is by far the most important

numerically, causing large numbers of childhood

deaths from dehydration. Its severity varies from chol-

era, in which the stool output may be up to 1 l h

1

(for

electrolyte losses, see Table 1), to other infective con-

ditions in which stool losses are smaller, although

potentially life-threatening. Treatment is usually by

oral rehydration therapy (see below), although severe

cases require intravenous or subcutaneous fluid re-

placement, where logistically possible. Formulae are

shown in Table 2 and are based on the principle that

small bowel sodium absorption is linked to that of

glucose. The presence of starch, polysaccharide, or

glucose in such formulae is vital. Amino acids and

peptides also enhance sodium reabsorption.

Vomiting or Nasogastric Aspiration

0010 An examination of Table 1 reveals the likely loss of

electrolytes from vomiting or nasogastric aspiration

and the logical replacement requirements. Aspirate

volumes must be measured and replaced appropriately.

Intestinal Fistula or Short Bowel Disease

0011 Up to 4 l per day may be lost from an upper jejunal

or duodenal fistula. Parenteral nutrition is almost

mandatory in this situation and must be combined

with adequate salt and water replacement guided by

measured losses, daily weight changes, plasma elec-

trolyte measurements, and a knowledge of electrolyte

concentrations in the fluid lost. Lower bowel fistula

or short bowel can be treated by the enteral route,

enhancing water and salt absorption using principles

similar to those used in oral rehydration therapy. If

enteral tube feeding is employed, a feed with sodium

content less than 90 mmol causes net sodium secre-

tion into the jejunum, whereas levels greater than this

are associated with net absorption. The presence of

carbohydrate and protein ensures the additional

effect of glucose and amino acids on sodium absorp-

tion. The rate of administration may also be import-

ant. Too rapid rates may overwhelm the capacity of a

shortened bowel to absorb all the fluid presented to it.

The total osmolar content should also be considered,

although the number of osmoles administered per

unit time is more important than concentration.

Metabolic and Renal Disorders

0012The hyperglycemia of diabetes mellitus causes an

osmotic diuresis, leading to large deficits of water,

sodium and potassium during acute loss of control,

e.g., diabetic ketoacidosis. An osmotic diuresis may

also result from excessive urea production owing

to excessive protein administration. Hypercalcemia

poisons distal tubular function, leading to excessive

production of dilute urine. Diabetes insipidus owing

to a lack of antidiuretic hormone (ADH) has already

been referred to. Alcohol excess dehydrates through

inhibition of ADH. Acute or chronic renal damage

may be associated with tubular dysfunction, loss

of renal concentrating capacity, and water and salt

deficit. This may be observed most strikingly in the

polyuric phase of recovery from acute renal failure or

following relief of obstructive uropathy. Treatment

consists of the appropriate administration of water

and electrolytes either orally or intravenously.

Excessive Use of Diuretics

0013Excessive use of diuretics is a common cause of water,

sodium, and potassium depletion in the elderly and

results from regimens that are too rigid and from lack

of patient education. Patients need to know, for

example, that if they fall ill from some condition

that prevents salt and water intake or leads to excess

loss, they should stop their diuretics.

tbl0002 Table 2 Concentration of electrolytes in oral rehydration solutions

Sodium (Na

)

(mmoll

1

)

Potassium (K

)

(mmoll

1

)

Chloride (Cl



)

(mmoll

1

)

Citrate or bicarbonate

(mmoll

1

)

Glucose

(mmoll

1

)

For mild to moderate diarrhea 35–60 13–25 50 10–20 100–200

For severe diarrhea 90 20 80 10 111

Glucose may be substituted by sucrose, maltose or rice water according to local availability.

1742 DEHYDRATION

Excessive Sweating

0014 Excessive sweating, e.g., in the tropics, merits appro-

priate replacement. Before adaptation takes place,

those going from temperate to hot climates are

particularly prone to dehydration and heat stroke. A

liberal water intake, combined, if necessary, with

additional salt, should be taken prophylactically.

Errors in Diagnosis

0015 Errors in diagnosis are particularly common in already

hospitalized patients who are more often the victims of

excess fluid administration than of dehydration. This

results commonly from a naı

ve interpretation and reli-

ance on one or more physical signs, e.g., dry mouth, or

from a failure to understand the compartmental distri-

bution of body fluids and how these are affected by

disease. A proper understanding of simple fluid balance

concepts is a prerequisite for managing the many con-

ditions in which dehydration or salt and water deple-

tion are common. Salt and water are also intrinsic

components of food and of the regimens used in the

nutritional support of the sick.

Oral Rehydration Therapy

0016 Solutions enhance the absorption of water and electro-

lytes through their substrate content, e.g., glucose,

while replacing electrolyte deficit safely, e.g., avoiding

hypernatremia in infants. They should be palatable and

acceptable to children, readily available and simple to

use under all conditions. An alkalizing agent to counter

acidosis may be advantageous. Solutions used in the

UK for mild to moderate diarrhea contain less sodium

and more glucose than the World Health Organization

(WHO) formula, which is used for severe diarrhea, e.g.,

cholera. Dose is according to fluid loss, but a rough

guide for adults is 200–400 ml for every loose stool, for

children 200 ml per motion, and for infants 1–1.5 times

the usual feed. In severe cases, doses may be higher. The

WHO policy is to promote its own single oral rehydra-

tion solution and to prevent hypernatremia in children

by giving extra water between doses. For further

details, see British National Formulary.

See also: Potassium: Physiology; Renal Function and

Disorders: Kidney: Structure and Function; Sodium:

Physiology; Water: Physiology

Further Reading

Guyton AC (1991) Textbook of Medical Physiology. Phila-

delphia, PA: WB Saunders.

Hladky SB and Rink TJ (1986) Body fluid and kidney

physiology. Physiological Principles in Medicine Series.

London: Edward Arnold.

Turnberg LA (1992) Pathophysiology of secretory diar-

rhoea. Hospital Update 18: 93–104.

Walters G (1983) Disorders of fluid and electrolyte balence.

In: Williams DL and Marks V (eds) Scientific Founda-

tions of Clinical Biochemistry: Biochemistry in Clinical

Practice, pp. 1–23. London: Heinemann.

DENTAL DISEASE

Contents

Structure of Teeth

Etiology of Dental Caries

Role of Diet

Fluoride in the Prevention of Dental Decay

Structure of Teeth

M E J Curson and M S Duggal, University of Leeds,

Leeds, UK

This article is reproduced from Encyclopaedia of Food Science,

Background

0001 The teeth comprise the hardest structures of the

human body and as such, once fully formed, change

little throughout life. Their resistance to destruction is

such that they play a major role in archeological and

forensic studies. Teeth as archeological remains are

well known to survive for thousands, if not millions,

of years after the death of the animal of which they

were a part.

0002Despite their apparent indestructibility in relation

to physical damage, and the ravages of time as

skeletal remains, the teeth are susceptible to chemical

damage during life by acid dissolution, a process

known as dental caries. This disease has occurred in

DENTAL DISEASE/Structure of Teeth 1743

humans for as long as they have existed. Even in the

earliest human skull specimens, the teeth show signs

of dental decay, albeit of a limited extent, with only

one or two cavities occurring in the mouth of an

individual. The susceptibility of the teeth to dental

caries has therefore always been present, but the

prevalence and incidence of the disease have varied.

This will be discussed more fully elsewhere, but an

understanding of the dental caries process is based

upon a knowledge of the structure of the teeth,

which is discussed in this article in overall terms of

the teeth and the components that make up a tooth.

Teeth

0003 In all mammals, there are two sets of teeth; in

humans, a primary (baby) or deciduous set of 20

teeth is replaced between the ages of 6 and 12 by

a secondary or permanent set of up to 32 teeth.

Primary Teeth

0004 The primary teeth are laid down in utero and com-

mence calcification at or immediately after birth. The

first teeth to erupt are usually the incisors at about

6 months of age, and the final primary teeth to come

into the mouth are the second molars between the

ages of 2 and 3 years.

0005 The primary teeth have the same basic structure as

the permanent teeth, i.e., enamel, dentine, cementum,

and pulpal (nerve) tissue. However, the overall

morphology of a primary tooth does differ somewhat

from the permanent successor. The major difference

lies in the crown, particularly of the primary molars,

which are more bulbous. The bulbosity is most

pronounced on the first primary molar in the lower

jaw, or mandible.

0006 The roots of the primary teeth are shorter, smaller,

and, in the molar, more curved than the permanent

successors. There is therefore less dentine in a primary

tooth. As the enamel is also thinner than in perman-

ent teeth, so dental caries progresses through to the

nerve faster in primary teeth. Furthermore, as the

nerves or pulps of the primary teeth are relatively

larger and more prominent, so the risk of abscess, as

a result of caries penetrating through to the pulp is

that much greater.

Permanent Teeth

0007 In a full set of permanent teeth, there are 32, although

not all teeth always develop, so one or several teeth

may be missing. The commonest tooth to be absent is

the third molar, or wisdom tooth.

0008 The morphology of the permanent teeth is very

similar to the primary teeth, but larger and with

much bigger roots relative to crown size. The enamel

is also much thicker. The dentine comprises the bulk

of a permanent tooth and becomes thicker with age.

This is because, as teeth age, the wear on the outside

of the enamel caused by eating slowly removes the

enamel. In wearing away the tooth, the masticated

foods produce a response in the nerve, which is slowly

reduced as dentine is produced by the odontoblasts.

In time, the nerve can shrink to the extent that the

pulp chamber almost disappears. Where a coarse,

abrasive diet is used, this process of laying down

secondary dentine can occur earlier in life and at a

much faster rate.

Structure of Teeth

0009The differences in the structure between primary and

permanent teeth are therefore those of size and thick-

ness. The chemical compositions of the enamel, den-

tine, and cementum of primary and permanent teeth

are essentially the same. As the chemistry of their

structure affects their subsequent resistance or sus-

ceptibility to dental caries, it is appropriate to discuss

their structure in detail.

Enamel

0010Tooth enamel comprises a hard, porcelain-like cap

covering the whole of the clinical crown of a primary

or permanent tooth. The crown is defined as that part

of a tooth that is erupted and is visibly present in the

mouth. It is distinct from the anatomic crown. How-

ever, with age, as the tooth continues to erupt, the

clinical crown becomes the same as the anatomic

crown.

0011The enamel comprises calcium, phosphate, water

(as OH) of a form known as hydroxyapatite (Ca

(PO

)

. 2OH). This basic chemical structure is wide-

spread in the animal kingdom and is the building

block of all calcified tissue. Where enamel is unique

is that the percentage of inorganic component making

up enamel is higher than any other tissue. Analysis of

enamel shows that an average of 98% is made up of

the inorganic component, largely the hydroxyapatite.

(See Calcium: Physiology.)

0012Developing enamel, which is of ectodermal origin,

is composed of up to 18% calcium and heterogeneous

proteins. The majority of the developing enamel

matrix consists of amelogenin, which is protein-rich.

The remainder of the enamel protein is a high-

molecular-weight phosphoprotein, known as enam-

elin. As the enamel continues to develop, the

amelogenin is replaced as the enamel calcifies and

then matures. During this process, over 90% of the

amelogenin is removed. If this process does not occur

properly, e.g., during some metabolic disorders,

enamel hypoplasia occurs. At a later stage, if

1744 DENTAL DISEASE/Structure of Teeth

calcification does not proceed properly during matur-

ation, hypocalcification results. In both instances, the

tooth may be more susceptible to dental caries.

0013 Mature enamel consists of enamel crystallites of

the aforementioned hydroxyapatite. These crystal-

lites mature rapidly in width but slowly in thickness.

The end result is a crystallite of large size.

0014 The crystallinity of enamel varies, depending on

its purity and the degree of incorporation of other

elements. However, enamel is never a pure substance

and always includes other inorganic or organic com-

ponents during the developmental stage. The main

component of interest is fluoride, which may be sub-

stituted for part of the hydoxyl ion to form fluorapa-

tite. This is of considerable interest in dentistry, as this

change produces an enamel that has a much greater

resistance to acid dissolution. The incorporation of

fluoride in the enamel will also provide a reservoir

of fluoride ion, which plays a role not only in resisting

dissolution but more importantly in remineralization.

0015 The crystallinity is affected not only by incorpor-

ation of other ions, but also in surface enamel and

in physicochemical ionic exchanges. Posteruptively,

these changes in enamel chemistry are notably influ-

enced by the uptake and release of fluoride and a

reduction in carbonate. The latter is about 2.5% by

weight, compared with calcium at 36% and phos-

phorus at 18%. However, it is felt that the carbonate

component, as it is less stable than pure hydroxyapa-

tite, may lead to a disruption of the enamel crystallin-

ity and probably play an important role in enamel

maturation. It is felt that as carbonate is more acid-

labile than other components, it is lost during early

caries or may make a high-carbonate enamel more

susceptible to acid dissolution.

0016 Enamel is laid down during development by

specialized cells called ameloblasts, and if a higher

concentration of fluoride is available in the blood-

stream, this trace element becomes incorporated by

the ameloblasts in the developing enamel. This mech-

anism is important when discussing the resistance of

enamel to dental caries, but also in the formation of

mottled enamel associated with high fluoride intake.

0017 As mentioned above, enamel is laid down by ame-

loblasts by a process of secretion of an enamel matrix,

which then becomes calcified. Further calcium and

phosphate salts are laid down as the enamel matures

prior to, and soon after, eruption in the mouth.

During this period of maturation, the enamel appears

to be more susceptible to acid dissolution, demineral-

ization, and the development of carious cavities. The

carbonate content of such enamel is high; carbonate is

subsequently lost during maturation, but this will be

offset by incorporation or the presence of fluoride in

the oral environment.

0018The enamel surface of the outermost layers of

10 mm is of a slightly different histological structure.

During the formation of the enamel, the ameloblasts

lay down an outer ‘surface layer’ of different, higher

mineral composition. If an increased level of fluoride

is incorporated in this layer, that tooth will have a

greater resistance to subsequent decay. Even during

the process of early demineralization, this ‘surface

zone’ remains intact, probably by a process of con-

tinuous remineralization by inorganic ions released

from the inner layers of enamel as it dissolves. During

the early stages of demineralization (caries), when the

inner layers of enamel are dissolved, the outer layer

retains its structure but becomes whitish in appear-

ance when seen clinically. This is known as a ‘white

spot’ or ‘incipient caries’ and is the first clinical sign

of decay, but can be reversed by remineralization. The

rate at which demineralization occurs will depend not

only on the level and frequency of acid attack but also

on the resistance of the enamel. This in turn will

depend on the degree of mineralization, maturation,

and fluoride and carbonate content.

Dentine

0019The major part of a tooth is dentine. The structure is

laid down by cells called odontoblasts, which secrete

tubules of dentine from the junction with the enamel

to the nerve or pulp of the tooth. The odontoblasts

are mesenchymal in origin and the structure they lay

down has a lower level of mineralization, as well as

smaller crystallites than enamel.

0020The dentine differs from the enamel in compos-

ition, being only 79% inorganic, although this

inorganic material is the same hydroxyapatite as in

the enamel and resembles bone in composition. The

higher organic component consists of collagen type I,

making up the walls of the dentine tubules and the

dentine process in the centre of the dentinal tubules.

0021Unlike enamel, dentine has an innervation by

means of nerve endings located at the pulpal end of

the dentinal tubules. It is for this reason that pain is

experienced when dentine is exposed in the mouth.

This exposure may occur as part of the carious pro-

cess when weak or undermined enamel breaks away

to form a cavity. Alternatively, when a cavity is drilled

by a dentist, in the process of removing decay, the

sensitive dentine is cut, also causing pain unless some

form of anesthesia is used.

0022Because of the higher organic content of the den-

tine, the process of dental decay is somewhat different

to that of the enamel. While the caries in enamel

is almost entirely a chemical dissolution by acids

produced by bacteria, such as Streptococcus mutans,

a secondary process of proteolytic removal of the

collagen occurs in dentinal caries.

DENTAL DISEASE/Structure of Teeth 1745