Page 305 - Pharmacognosy 2 PG303

Pharmacognosy-2 (PG303) Level 2 Clinical Pharmacy-Pharm D

by injury or by unfavourable conditions of growth and are usually formed by
changes in existing cell walls. The conversion of the cell walls of a tissue into gum
is known as Gummosis. It occurs either normally in the Ceratenchyma and phloem
parenchyma or induced by wounding the stem where gummosis appears to take place
in the cambium or young phloem tissue.

Chemically, Gums consist of calcium, potassium, and magnesium salts of
complex substances known as polyuronides, and can be hydrolysed by prolonged
boiling with dilute acids to yield mixtures of sugars and sugar acids. The sugars so
given are monosaccharides, usually pentoses such as arabinose and xylose, or
hexoses such as galactose. The sugar acids, liberated by hydrolysis, are known as
uronic acids.

Notes
• Pectin and Hemicellulose, also yield on hydrolysis sugars and uronic acids,

thus showing a relationship with gums. Pectin consists mainly of pectic acid and
almost completely soluble in water forming a viscous colloidal solution. One part of
pectin heated in 9 parts of water forms stiff gel. Certain commercial gums are
actually hemicellulose such as Carob and Guar gums.

• Mucilage are similar in constitution to gums but are normal products of cell
activity, being secreted in the cell and laid down like hemicellulose, often in such
quantity as to completely fill the cells. They are insoluble in water but form slimy
mass with it (c.f. Gums).

• Artificial gums or Dextrin are produced from starch by enzymatic or
incomplete acid hydrolysis. They differ essentially from gums in being entirely
converted into dextrose by dilute mineral acids, and are strong dextrorotatory, while
natural gums are slightly laevorotatory.

The most important gums are Gummi Arabicum and Gummi Tragacanthae
which are official in the Egyptian Pharmacopoeia.

Gum Arabic

Syn.: Gum Acacia; Acacia; Acaciae Gummi, Gummi Arabicum

Gum Arabic is the dried gummy exudation obtained from the stem and
branches of Acacia senegal (Lin.) Willd., or of some other African species of
Acacia (Fam. Leguminosae, Mimo-soideae).

The plant is a small tree attaining a height of 5-6 metres and growing freely
both in Western Africa and in Eastern Africa (the upper Nile districts), possibly also

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