It is an exudation product of the plant and they are complex polysaccharides and amorphous, containing methyl pentose, hexoses and uronic acid residues joined by glycosidic linkage. Ex. gum acacia, plum gum, guar gum.
Occurrence of Gum:
Gums occur as exudate from the bark, leaves, stem and wounded part of plant as metallic salt of Na, K and Ca.
Chemical Nature of Gum:
1) Neutral salt of complex polysaccharide and branched chain nucleus of uronic acid (gluconic acid) residues
2) On hydrolysis with boiling water and acid split gums into uronic acid and some sugars (xylose, arabinose, fructose, glucose).
Properties of Gum:
Acidic in reaction, swells in water, Amorphous, soluble in water, form gel, insoluble in organic solvents, form salt with basis like Ca, Na, K.
Physiological Role of Gum:
Gums absorb water greatly and hence they hold water in plant tissues.
1) Gum Arabic (Acacia) exudate from bark of acacia
2) Damson Gum – from bark of Damson plum tree
3) Tragacanth Gum – from leguminous plants
4) Guar Gum – obtained from guar plant
5) Microbial Gum – from capsules of certain bacteria.
Uses of Gum:
Used in large scale in medicine and wood industry, manufacture of chewing gums