1 66 THE CARBOHYDRATES 



known as dextrin. The use of starch for stiffening hnen 

 depends on some such similar change produced in the starch 

 by the heat of the iron. 



Although a great many different dextrins have from time to 

 time been described, comparatively few of them are sufficiently 

 well defined to warrant any description here. 



Amylo-dextrin. — This substance is obtained by the action 

 of ungerminated barley diastase at 50° C. and precipitated by 

 alcohol. It is a white powder slightly soluble in cold water, 

 but readily in hot. It is strongly dextro-rotatory (^j, = + 196) 

 does not reduce Fehling's solution, and gives a blue colour with 

 iodine. 



Erythro- dextrin. — This is a solid which dissolves readily in 

 water, has a rotatory power of ^j, = + 196°, and with iodine 

 produces a red-brown colour. 



The existence of erythro-dextrin as a chemical entity is, 

 however, disputed by Ost, who says that it is a mixture of 

 achroo-dextrin with starch ; an artificial mixture of achroo- 

 dextrin with | per cent of starch also produces a red colour 

 with iodine. 



Achroo-dextrin. — This substance is optically active, has the 

 value a^ — -]- 192°, gives no colour with iodine, and has a 

 sweetish taste. 



M alto-dextrin. — In addition to the above dextrins, Brown 

 and his collaborators, and Ling and Nanji * have described 

 the following malto-dextrins which are non-crystalline inter- 

 mediate products of the action of diastase on starch and pos- 

 sessing cupric-reducing power : malto-dextrin-cc CaeHgaOgi 

 (ajj=i8o°), and malto-dextrin-^, C24H4.202it (au — I73"5°), 

 and stable dextrin. X 



According to Ling and Nanji, malto-dextrin-a is an inter- 

 mediate product in the degradation of aj3-hexa-amylose to 

 j3-glucosidomaltose (see p. 156), and they regard the stable 

 dextrin of Brown as a malto-dextrin of the highest type. 



* Ling and Nanji : "J. Chem. Soc, Lond." 1925, 127, 636. 

 t Ling and Baker : id., 1895, 67, 703 ; 1897. 71, 517. 

 + Brown and Millar : id., 1899, 75, 286. 



