Synonyms British Gum; Starch Gum; Leiocom; Pyrodextrin; Torrefaction dextrin; Canary dextrin; Yellow dextrin; White dextrin.
Preparation Dextrin is prepared by carrying out the incomplete hydrolysis of starch with dilute acid or by heating dry starch.
Various types of dextrin are prepared as detailed below namely:
(a) British Gum, Starch Gum: It is produced at high temperature in the absence of acid.
Characteristic features:
(i) Dark brown colour, odourous,
(ii) High viscosity, very soluble in cold water,
(iii) Does not reduce Fehling’s Solution, and
(iv) Gives reddish-brown colour with iodine.
(b) Canary Dextrin, Yellow Dextrin: It is prepared by hydrolyzing starch at high temperature for a longer duration but in the presence of small quantum of acid.
Characteristic features:
(i) Light brown to yellow colour, slight odour, and
(ii) Low viscosity, very soluble in cold water.
(c) White Dextrin: It is prepard by hydrolysis at low temperature for a shorter duration but in the presence of large quantum of acid.
Characteristic features:
(i) White colour, odourless,
(ii) Slightly soluble in cold water, and gives a red colour with iodine, and
(iii) Very soluble in hot water and gives a blue colour with iodine.
Uses
1. As an excipient for dry extracts and pills.
2. It is used for preparing emulsions and dry bandages.
3. It is employed for thickening of dye-pastes and mordants used in printing fabrics in fast colours.
4. It is used for sizing paper and fabrics.
5. It is employed for preparing felt and printing tapestries.
6. It is used for preparing printer’s inks, glues and mucilage.
7. It is employed for polishing cereals.
8. It is extensively used in making matches, fireworks and explosives.
