Dextrin

Dextrin (C₆H₁₀O₅), an isomer of starch (q.v.), from which it is readily prepared. When starch is heated for some hours in an oven, or for thirty minutes to the temperature of 213° C. the grains swell, burst, and turn into a pale brownish substance known as torrefied starch, British gum, or commercial dextrin. It appears either in translucent masses or as a powder. With iodine it gives a fine purplish-red colour. On the addition of cold water to it the dextrin dissolves readily, forming a clear gummy solution, leaving behind some unaltered starch. This gummy solution is largely used in calico-printing and as a substitute for gum-arabic, as on our postage stamps. Dextrin being as insoluble in alcohol as it is soluble in water is precipitated from the solution on the addition of that substance, forming white flocculent masses uniting into translucent colourless lumps. This pure dextrine is not coloured by iodine. Dextrin is formed in baking, often constituting 10 per cent. of bread, and giving a glaze to loaves and biscuits. It is also formed from starch, and even from cellulose (q.v.), by the action of acids and of nitrogenous ferments (q.v.), or zymosis, such as diastase (q.v.), as in the germination (q.v.) of seeds, or that artificially stimulated germination known as malting (q.v.). Dextrin occurs, therefore, in beer. It has also been found in the flesh of animals. It is suggested that some ferment is present in every cell, and that the transformation of starch by its action into dextrin may be a widely important process of digestion preparatory to the transfer of the carbohydrate food to another part of the organism.