FOODS 105 







cellulose. Alcohol precipitates a white powder (soluble 

 starch) from the aqueous solution. The blue coloration 

 produced by iodine is characteristic of starch. Heat 

 discharges the coloration, but it reappears on cooling. 

 By dilute acids, starch is converted into dextrin, maltose, 

 and dextrose ; by diastase, into maltose and dextrin, as 

 shown above ; and by the saliva, into dextrin and maltose. 



Dextrin is really a name which denotes several isomeric 

 substances usually found in mixture and resembling each 

 other very closely. They form gummy amorphous masses 

 whose aqueous solutions are dextro-rotatory, hence the 

 name dextrin. They do not reduce Fehling's solution 

 and are not directly fermented by yeast, but in the presence 

 of diastase, the dextrin is changed to dextrose and then 

 fermented. They give a red colour with iodine, and are 

 much used as substitutes for natural gums. 



Inulin is a polysaccharid found in the roots of dahlia, in 

 chicory, and in many compositae. It is a white powder, 

 soluble in boiling water to a clear solution. It gives a 

 yellow colour with iodine. When boiled with water it is 

 completely changed to fruit sugar (laevulose). 



Glycogen occurs in the liver of mammals. It is a mealy 

 powder, soluble in hot H 2 O, gives a reddish-brown colour 

 with iodine ; ferments change it to maltose, and dilute acids 

 to dextrose. It is precipitated from solution by alcohol. 



Raffinose, or Melitose, is a trisaccharid found in Australian 

 manna, in the flour of cotton seeds, in small amounts in 

 sugar beets, and is crystallized from the molasses. It is 

 very soluble, is dextro-rotatory, is easily fermented with 

 yeast, but does not reduce Fehling's solution. 



Arabinose was formerly thought to be a glucose, but is 

 really a pentose ; that is, contains but five carbon atoms. 

 It is made from gum arabic by boiling with dilute sulphuric 

 acid. It crystallizes in prisms, is slightly soluble, is dextro- 

 rotatory, reduces Fehling's solution, but does not ferment 

 with yeast. Boiling mineral acids convert it into furfurol. 



Mannite, or Mannitol, exists in three states, namely, dex- 

 tro, laevo, and inactive. It has a sweet taste and is found in 

 " manna," the dried sap of the manna ash (Fraxinus ornus). 

 It is also made (with difficulty) by the action of nascent 

 hydrogen on glucose. It oxidizes to saccharic acid. 



