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78 Textbook of Pharmacognosy
America and South – West North America but only a few are commercially
important.
Geographical Source
The oldest and best known of all the natural gums is gum arabic. The tree
Acacia senegal grows wild in Sudan, Central and West Africa. Gum acacia
originally belongs to Senegal gum, Sudan gum, Kordofan gum or Egyptian
gum which is superior and always preferred to any other known gum.
The plants are grown in Senegambia in West Africa, the upper Nile region
in Eastern Africa and Central Africa. The trees grow wild throughout Sahel
from Senegal to Sudan to Somalia. Today the gum is harvested in
Mauritania, Senegal, Masli, Burkina Faso, Niger, Nigeria, Chad, Cameroon,
Sudan, Eritrea, Somalia, Ethiopia, Kenya and Tanzania. The plant has been
historically cultivated in Arabia and West Asia. Acacia nilotica (= Acacia
arabica) (Babul tree) grows wild in India in the states of Punjab, Rajasthan,
Andhra Pradesh and Tamil Nadu.
Collection and Preparation
The gum has been harvested in Arabia, Egypt and West Asia since antiquity,
and sub-Saharan Africa has a long history as a prized export. The gum
flows naturally from the cracks on the bark of the tree under difficult
conditions like heat, dryness, wounds and diseases. This flows naturally
in the form of a thick and frothy liquid and concretes in the sun into tears.
The gum is traditionally harvested by the semi-nomadic desert tribes while
on their travels. The hardened exudations are collected in the middle of
the rainy season (harvesting begins in July) and exported at the start of the
dry season (November). Acacia senegal is tapped for the gum by cutting
holes or incisions (60 × 5 cm) in the bark from which a product called
Senegal gum (kordofan) is exuded. Seyal gum from Acacia seyal (the species
more prevalent in South Africa) is collected from naturally occurring
exudations on the bark.
The gum is produced as result of injury to the plant. After the rainy
season the bark of the trees is tapped and transverse cuts are made on the
stem and branches to expose cambium. As a result of injury, tears of gum
are collected on the cambium and newly formed phloem. The gum droplets
are about 0.75–3 cm which gradually dry and harden which are manually
collected. Within 20–30 days the tears of gum which have formed on the
surface may be picked up, made free of bark pieces and foreign organic
matter. The material thus collected may be dried in the sun which helps in
the removal of moisture. During the process of sun drying numerous cracks
appear on the surface of lumps of tears and the gum is bleached. In general,
higher the temperature, the higher is the yield. Damaged trees give larger
yield of the gum. The yield is improved by natural factors that lessen the
Systematic Pharmacognostic Study of Carbohydrates and Derived Products 79
vitality of the trees like hot weather, poor soil and lack of moisture. The
gum is further processed into the final products. These include ‘kibbling’
(making the uniform pieces of pebble size), granulating, powdering and
spray drying. During kibbling, the large lumps of gum are passed through
a hammer mill and it is screened to produce smaller granules of more
uniform size. The dissolved gum (in water) is filtered for the removal of
contamination, and is sprayed into a stream of hot air to promote the
evaporation of water and the powder is screened to assure the uniformity
of the size of the particles. The crude gum is stored and exported in jute
sacks while the graded gum is packed in heavy duty bags. The semiprocessed and processed granules are exported in drums, polyethylene –
lined, multi-wall paper bags or cardboard boxes. When stored in cool
(21–24°C) in a dry place the gum has an unlimited shelf-life.
Characters
Gum Arabic is colourless (somewhat yellowish), tasteless (bland taste),
non-toxic, odourless, acidic (neutral or slightly acidic salt), white powder.
It is insoluble in oils and in most organic solvents, but usually dissolves
completely in hot or cold water forming a clear, mucilaginous solution.
The gum is available in tears, crystals, granules, powder, and spray- and
roller-dried powder. It is a multifunctional and a complicated mixture
of long and short chains of sugars (arabinogalactan of arabinose and
galactose monosaccharides, oligosaccharides and polysaccharides) and
glycoproteins of a very high molecular weight. This is a major component
of many plant gums including gum arabic. 8–5’ non-cyclic diferulic acid
has been identified as covalently linked to carbohydrate moieties of
the arabionoglactan-protein fraction. The hydrolysis of gum yields
L-arabinose, L-rhamnose, D-galactose and D-glucuronic acid. This is very
unique among the naturally occurring hydrocolloids because of its high
Gum acacia tears
Gum powder and lump
80 Textbook of Pharmacognosy
Gum acacia powder
Gum acacia salt
solubility in cold water. It forms sticky glue when mixed with water. It has
a low viscosity and adhesive properties. This is insoluble in oils and most
organic solvents. It is soluble in aqueous 60% ethanol. With glycerol and
ethylene glycol it has a limited solubility.
Chemical Constituents
Gum Arabic is a complex mixture of saccharides and glycoproteins which
give it the properties of glue and binder. Acacia gum consists mainly of
arabin, the calcium salt of Arabic acid along with varying amounts of
magnesium and potassium salts of the same acid in addition to smaller
amounts of other salts of these bases. The gum (arabino-galactanC
20H36O14
) is built upon a backbone of D-galactose units with side chains
of D-glucuronic acid with L-rhamnose or L-arabinose (C12H22O11) terminal
units. The molecular weight is large in the range of 200,000 to 600,000
daltons. It is soluble in water but does not dissolve in alcohol. Arabic acid
on hydrolysis gives L-arabinose, L-rhamnose, D-galactose and
D-galactose (C6H12O6)
L-rhamnose (C
6H12O5
D-lucuronic acid (C
)
L-arabinose (C5H10O5)
6H12O7
)
Systematic Pharmacognostic Study of Carbohydrates and Derived Products 81
D-glucuronic acid. Acacia also contains an oxidase enzyme and about 14%
(12 to 17%) of water and a trace of sugar. It yields about 2.7–4.0 % of ash
entirely of calcium, magnesium and potassium carbonates.
History of Gum Arabic
Gum Arabic was an important article of commerce as early as the 12th
century BC. Herodotus in his writings (5th century BC) mentions its use in
embalming in Egypt. In the 9th century, the Arab physician, Abu Zayd
Hunayn ibn Ishaq al-Ibadi in his ‘Ten Treatises on the Eye’ described gum
arabic as an ingredient in poultices for the eye. In Turkey, the gum was
used in the application of gold to manuscripts and they mixed 24-carat
gold leaf with melted gum arabic to make gold paste. It was known that
the Turkish scribes made lampblack ink with this gum and water. In ancient
times, it was used for mummification and inks for hieroglyphics.
Medicinal Uses
Gum Arabic is a demulcent. Its demulcent properties are employed in
various cough mixtures, diarrhoea and throat preparations. As it is capable
of soothing the irritated mucous membranes, it is used in the preparation
of cough drops and lozenges. It is also administered intravenously in
haemolysis. In the form of mucilage, it is used as a suspending agent,
specifically in mixtures with resinous substance. Gum Arabic is a good
emulsifying agent for fixed oils, volatile oils and also for liquid paraffin. It
is a good binding agent and is used in the preparation of lozenges, pastilles
and compressed tablets. It is a gum of choice, as it is compatible with other
plant hydrocolloids, as well as starches and carbohydrates. In combination
with gelatin, it is used to form coacervates for microencapsulation of drugs.
It is used in intestinal dialysis and cosmetics. Pharmaceutically, it is used
in the manufacture of capsules, for coating the pills, in the manufacture of
vitamins, mascara and other cosmetics. This is used to treat bleeding,
bronchitis, gonorrhea, typhoid fever and infections of the upper respiratory
tract because of its astringent properties. Sometimes, this is also used to
lower the levels of cholesterol, which is not validated. The gum slows the
rate of absorption of some drugs like amoxycillin from the gut.
Non-medical Uses
a. Culinary and dietary uses: Gum acacia is highly nutritious and about
6 ounces of the gum supports an adult desert animal like Moor for
24 hours. It is an important ingredient of soft drink syrups, gummy
candies, chocolate candies, etc. This has an ability to reduce the surface
tension of the liquids leading to increased fizzing and as such it can
be used in the production of diet cokes. In the preparation of
beverages, it helps oil-based flavours to remain evenly suspended in
82 Textbook of Pharmacognosy
water. In confectionery, it keeps the oil flavor and a fat uniformly
distributed, prevent crystallisation of sugar and thickens chewing
gums and jellies. It is used to enhance the shelf-life of flavours in dry
packaged products like instant drinks, dessert mixes and soup bases.
It is capable of smoothing the creams, fixatives and lotions in
cosmetics. It is used in sweeteners and as an additive in foods and
beverages, as a thickener in liquids like soft drinks and food flavours.
It has a low viscosity and high adhesive properties that make it an
excellent ingredient for coating cereals, confectionaries and snack
foods. In bakery products, it is used in icings and frostings. In food,
the gum is used as a stabiliser. It is edible. The Arab populations use
the natural gum to make a chilled, sweetened and flavoured gelatolike dessert. New foliage is used as forage while the dried seeds are
consumed by the humans. It is an excellent source of soluble dietary
fibre.
b. Use in artistry, lithography and photography: It is also used as a
permanent binder to fix the pigments onto the surface of the
paper by the artists in water colour paints. It is used for gum
printing in photography to bind the pigments and to create
coloured photographic emulsions which are sensitive to
ultraviolet light. Nowadays, it is used in lithography as it helps
as an antioxidant coating for photosensitive plates. This has been
used since ancient times as part of the black ink. The ancient
Egyptian ink was made of carbon soot form the lamps or burnt
plant material apart from water and gum arabic. Written on paper
or papyrus, this ink has survived for over 3000 years. Because the
gum dissolves easily in water, it is used as a binder for water
colour printing.
c. Other uses: The gum is used as a water-soluble binder in fireworks.
It is an important constituent of shoe polish and used in home-made
incense cones. It is used as an adhesive on postage stamps and
cigarette papers. It can also be used as a flocculating agent in refining
the ores, in microencapsulation to produce carbonless copy paper,
scratch-and–sniff perfume advertisements, laundry detergents,
baking mixes, etc. It also finds it use in sizing and finishing the
textiles and for inhibition of metal corrosion. Non-culinary uses
include the production of fireworks, paints, inks, glues, ceramic
glazes, textiles, cosmetics and more. The roots of the plant nearer to
the ground as well as the bark of the tree are used in making strong
ropes and cords. The bark of the tree is rich in tannin and is used in
tanning and in the production of dyes and inks. Caution is to be
taken as very rarely, the gum may cause gas, bloating and loose
stools when used as a supplement in addition to some allergic
reactions.
Systematic Pharmacognostic Study of Carbohydrates and Derived Products 83
Harmful Effects
In particular when used in larger amounts, the gum may cause digestive
issues for some people. The potential side effects are: flatulence/gas,
bloating, unfavourable viscous sensation in the mouth, early morning
nausea, mild diarrhoea and other types of ingestion. To limit these side
effects, it is always better to keep the intake well below the maximum daily
dose of about 30 grams/day.
Adulteration
The crude gum is often adulterated by adding similar and inferior quality
gums which cannot be normally detected. For example, Mesquite gum
obtained from Prosopis juliflora and artificial gums made from starch or
dextrin and in the form of a fine powder, it is adulterated with starch and
white dextrin.
TRAGACANTH
Synonyms
Gum Tragacanth (English), Traganth (German), Gomme adragant (French),
Tragacantha, Angira (Hindi), Katila (Bengali), Shiraz gum, Gum elect, Gum
dragon, Syrian tragacanth, Hog gum, Goat’s thorn, Green dragon, Gummi
tragacanthae.
Biological Source
It is the dried gummy exudation (sap) obtained by incision from the bark
of stems and branches of several species of Middle Eastern legumes of
the genus Astragalus which include Astragalus gummifer Labill. and other
Asiatic species like A. tragacanthus, A. kurdicus, A. microcephalus, A. verus,
Gum tragacanth plant Gum extract
84 Textbook of Pharmacognosy
Tragacanth gum
As powder
A. adscendens and A. strobilifer (Family: Leguminosae–Fabaceae). The
words, tragos and akantha in Greek mean ‘goat’ and ‘thorn’ respectively.
Hence, the name ‘Goat’s thorn’ for the plant. Indian tragacanth (Sterculia
gum, Karaya gum) is obtained from Sterculia urens Roxb. and other
species. This was described by Theophrastus several centuries before Christ.
The gum has been officially recognised in the U. S. Pharmacopoeia
since 1820.
Geographical Source
Tragacanth grows wild in the dry deserts, highlands and mountains of
Turkey, Iran, Greece, Iraq, Syria and Russia. In India Astragalus species
grow in wild state in Kumaon and Garhwal regions of Himalayas. Iran is
the biggest producer of the best quality gum. The primary source is the
desert highlands of Northern and Western Iran, particularly, the Zagros
mountain region.
Collection and Preparation
The plant is a small, low, bushy, perennial shrub having a large tap root
which along with the branches is tapped for the gum. The plants require
abundance of water during the growing season, but need a dry climate
during the time of collection, which extends from April to September (for
ribbons) and from August to November (for flakes). The plants are tapped
by making careful longitudinal incisions in the tap root and the bark of the
branches. When the plant is injured, the gum exudes readily from these
cuts in the form of ribbons or flakes. The cell walls of the pith and then the
medullary rays are gradually transformed into gum. The gum absorbs water
and creates internal pressure within the stem, thus forcing it to the surface
through the incision that caused the injury. When the gum strikes the air,
it gradually hardens owing to the evaporation of the water and becomes
Systematic Pharmacognostic Study of Carbohydrates and Derived Products 85
brittle. The nature of the incision governs the shape of the final product.
The better grade comes from transverse incisions made with a knife in the
main stem and older branches. The gum from such incisions is known as
ribbon gum and flake gum, depending on the shape of the solidified
exudates. The gum usually shows longitudinal striations caused by small
irregularities in the incision. The metamorphosis occurs only at night, and
the tragacanth ribbons exhibit transverse striations that show the amount
that exudes each night. The whiter and more transluscent ribbons are
collected when the drying time is of shorter duration. The collections are
first brought to the trading centers and then to wholesale markets where
they are sorted by hand, graded, packed and shipped.
Characters
The gum is viscous, odourless and tasteless and is obtained during hot
season from the root of the plant and dried. The gum comes out of the
plant from natural injuries as white to pale-yellow, flattened, straight,
spirally twisted or coiled ribbons or worm-like flakes which can be
powdered (white to pale-yellow or pinkish brown). Sometimes, it will be
shaped like irregular tears of yellowish or brownish colour. Sometimes,
the pieces appear with a red tinge and horny in their structure.
The gum exudate varies in its quality from long, thin, white ribbon to a
coarse, yellow-tan ribbon. The powder made from the ribbon is white to
light yellow in its colour, odourless, and has an insipid, mucilaginous taste.
The flakes vary from yellow tan to brown to give yellowish white to tan
powders. This swells rapidly in either cold or hot water to a viscous,
colloidal sol or semi-gel which acts as a protective colloid and stabiliser. It
is insoluble in alcohol and other organic solvents. The gum can tolerate
small amounts of alcohol of glycols. The gum solutions are acidic in the
pH range of 5–6. It is fairly stable over a wide range of pH down to
extremely acidic conditions of about pH 2.0.
The viscosity is the most important factor in the evaluation of the gum
and is regarded as a measure of its quality as well as its behaviour (as a
suspending agent, stabiliser or emulsifier). The viscosity of 1% solution
may range from about 100–3500 centipose depending on the grade. The
viscosity reaches a maximum in 24 hours at 25°C, 8 hours at 40°C, and
2 hours at 50°C. The maximum initial viscosity is at pH 8.0, but maximum
stable viscosity is about pH 5.0. The viscosity of the gum solution is quite
stable over a wide pH range.
Chemical Constituents
It is a water-soluble carbohydrate gum with a molecular weight of
approximately 840,000, which contains the polysaccharides tragacanthin
(30–40% water-soluble) and bassorin (60–70% water-insoluble). Tragacanth
86 Textbook of Pharmacognosy
contains bassorin, a complex mixture of high molecular weight
polysaccharides (polymethoxylated acids, galactoarabans) which upon
hydrolysis yield D-galacturonic acid, D-galactose, geddic acid (C34H68O2),
L-arabinose, D-xylose and L-fucose, in addition to small amounts of
rhamnose and glucose as well as traces of starch and/or cellulose. Mannose
and glucuronic acid are absent. The gum is soluble in water and swells up
to form smooth, stiff, opalescent mucilage. In solution, it is acidic with a
pH of 5.0–6.0, and its maximum viscosity is at pH 8.0 but maximum stable
viscosity was found to be near pH 5.0 and stability decreases below 4.0 or
above 6.0. The portion soluble in water is chiefly polyarabinantrigalaetangeddic acid while the insoluble part is bassorin. Bassorin on
hydrolysis yields tragacanthose, xylose and bassoric acid. It is insoluble in
ethanol and does not swell in aqueous ethanol. Bassorin has an elongated
molecular shape and forms a viscous solution. The gum also contains water,
traces of starch, cellulose and nitrogenous substances yielding about 3%
ash. Tragacanthin, which is probably demethoxylated bassorin, composes
about 30% of the gum and is the more water-soluble component. The
aqueous suspension on microscopic examination shows many angular
fragments with either circular or irregular lamellae along with starch grains
and stratified cellular membranes.
L-Arap-, →2)β-L-Araf-, α-L-Araf-, →2)-α-L-Araf-,→3)-α-L-Araf-,→4)-α-
D-Galp-, →6)-α-D-Galp-, α-L-Araf-(1→2)-α-L-Araf-(1→4)-L-Ara, α-L-
Araf-(1→2)-α-L-Araf-(1→5)-L-Ara, β-D-Galp-(1→4)-[β-D-Galp-(1→4)]2-
D-Gal, β-D-Galp-(1→4)-β-D-Galp-(1→4)-D-Gal, β-D-Glcp-(1→4)-[β-D-
Galp-(1→4)]2-D-Galp, α-D-Glcp-(1→4)-[α-D-Glcp-(1→4)]
-D-Glc.
0.3
(The gum contains free α-Araf-(1→2)-α-Araf-(1→4)-Arap and α-Araf-
(1→2)-α-Araf-(1→5)-Araf, which correspond to side-chain structures
with α-Araf and Arap in the arabinogalactan. β-Galp-(1→4)-[β-Galp-
(1→4)]
-Galp, β-Galp-(1→4)-β-Galp-(1→4)-Galp, β-Glcp-(1→4)-[β -
2
Galp-(1→4)]2-Galp probably correspond to tragacanthic acid, and α-
Glcp-(1→4)-[α-Glcp-(1→4)]
Graphical structure of Gum tragacanth
D-xylose (C5H10O5) L-fucose (C6H12O5)
-Glc to starch).
0–3
Systematic Pharmacognostic Study of Carbohydrates and Derived Products 87
D-galactose D-galacturonic L-arabinose
(C
6H12O6
) acid (C6H10O7)(C
5H10O5
)
History of Tragacanth
Gum tragacanth is one of the oldest drugs known and has been in
commercial use for well over 2000 years, widely used in pharmacy and
industry down through the ages. It was described by Theophrastus three
centuries before Christian era. Dioscorides and Arabian writers gave it
due attention. In ancient times, it has been used as an emulsifier, thickening
agent and also a suspending agent. It was officially recognised in the US
Pharmacopoeia since 1820. In folk medicine, it has been used as a laxative,
and for the treatment of persistent cough, diarrhoea, and as an aphrodisiac.
It has been used for centuries in Chinese herbal medicine to overcome
fatigue, to lower the blood pressure, to treat colds, nephritis and
hypoglycaemia. It would be difficult to locate the first use of tragacanth as
the first use of wheat. It came into Smyrna form the interior of Asia Minor,
and from Persia and Armenia.
Medicinal Uses
The uses of Tragacanth are dependent on its high viscosity at low
concentration, suspending action, stability to heat and acidity, effective
emulsifying properties, and an extremely longer shelf-life. Gum Tragacanth
is used extensively in pharmaceutical products because of its thickening
power and stabilising action in suspended matter. It has no known
therapeutic action and is solely used as an excipient for tablets, as a
component of medicinal jellies and as laxative and in making emulsions. It
is used in the preparation of lozenges and styptic powder. It is very useful
in cases of irritation of the mucous membranes of the pulmonary and
genitourinary organs. It is also used as a vehicle for active medicines. Gum
is having demulcent, emollient and spermicidal properties. It is used to
treat coughs and diarrhoea. It is also employed in spermicidal jellies and
creams, which immobilise spermatozoa on contact. It is reported that
tragacanth gum exerts a strong inhibitory action on cancer cells. The
alkaloid within it is used as a remedy for cough and diarrhoea. As a paste
it is used as a topical treatment for burns. The mucilage of Tragacanth has
been used as an application to burns. The gum is used in the cod liver oil