STARCH 



155 



By acting on starch at the ordinary temperature with 

 12 per cent commercial hydrochloric acid for twenty-four 

 hours, Brown and Morris found that granules, while retaining 

 their external features, had acquired the power of dissolving in 

 hot water without the formation of paste. The addition of 

 alcohol to such a solution caused the immediate precipitation 

 of a white substance known as soluble starch, which is turned 

 blue by iodine, is strongly dextro-rotatory, [a],, = 202°, and 

 does not reduce Fehling's solution. On the other hand, if 

 starch is boiled for some time with dilute hydrochloric acid, 

 it is converted into glucose, a fact which is made use of in 

 estimating starch. 



That maltose is also produced as an intermediate product 

 of the acid hydrolysis of starch has been shown by Fernbach 

 and Schoen,* and also by Weber and Macpherson,t who have 

 proved it to be present in commercial glucose (see p. 97). 

 Accompanying the conversion of starch into glucose there is, 

 however, the formation of varying quantities of gummy sub- 

 stances known as dextrins (q.v.) ; it is, however, not known for 

 certain whether these dextrins are formed directly by the action 

 of the acid on the starch, or whether they are produced by the 

 condensing action of the acid on the glucose already formed ; 

 there is, moreover, great difference of opinion with regard to 

 the nature and number of these substances which are formed. 

 According to Nanji and Beazeley J some iso-maltose is always 

 formed during acid hydrolysis of starch. 



Action of Malt Diastase on Starch. 



The action of an extract of malt § on starch paste is 

 complex in that it involves liquefaction and saccharification.|| 

 These two changes are effected by different enzymes as is in- 

 dicated by keeping a mixture of starch paste and malt extract 

 at 70° C. After some minutes the paste becomes less viscous 



* Fernbach and Schoen : " Bull. Soc. Chim.," 1912, [iv], li, 303. 

 t Weber and Macpherson : "J. Amer. Chem. Soc," 1895, 17, 312. 



I Nanji and Beazeley : " J. Soc. Chem. Ind.," 1926, 45, 215 T. 



§ Barley malt has been shown to contain a great many different 

 enzymes capable of acting upon lichenin, mannan, cellobiose andmaltase, 

 etc. ; it is the action upon starch only which is here being considered. 



II Oblsson : " Zeit. physiol. Chem.," 1922, 119, i. 



