STARCH 153 



and Nanji have furnished further methods for distinguishing 

 between amylose and amylopectin ; they find that when starch 

 paste, warmed to 50° C, is treated with precipitated diastase, 

 prepared from ungerminated barley, and dried by means of 

 absolute alcohol, the amylose constituent is converted com- 

 pletely into maltose whilst the amylopectin is hardly acted 

 upon ; the maltose may be removed by dialysis leaving the 

 amylopectin. If, on the other hand, precipitated barley dia- 

 stase is used, which has not been dried by alcohol, amylo- 

 pectin also is attacked yielding a product to which they give 

 the name a^-hexa-amylose. 



A further distinction between amylose and amylopectin 

 was observed by Samec and von Haefft * who showed that 

 amylopectin contains, on an average, 0-175 per cent of P2O5 

 in organic combination as a carbohydrate ester of phosphoric 

 acid ; later Samec and Mayer f were able to demonstrate 

 that after the removal of the phosphoric acid from amylo- 

 pectin, the phosphorus free carbohydrate, to which they 

 gave the name of erythroamylose, could be re-esterified with 

 phosphoric acid to a viscous jelly which, however, contained 

 2-19 per cent P2O5. The same authors also showed that 

 amylose has a^ = 189°, while amylopectin has aj, = 195-196°. 



With regard to the relative amounts of the two constituents. 

 Ling and Nanji J claim to have established an almost constant 

 ratio of 66 per cent, amylose to 33 per cent of amylopectin, 

 while, on the other hand, Samec and Hofft claim that the pro- 

 portions in potato starch are 17 per cent of amylose to 83 

 per cent of amylopectin. 



In addition to amylose and amylopectin. Ling and Nanji § 

 have also found a substance described as amylohemicellulose 

 to be associated with cereal starch grains, but the quantity 

 varies considerably in different starches. 



To summarize our knowledge with regard to the two 

 constituents of the starch grain : — 



* Samec and von Haefft : " Kolloidchem. Beihef.," 1913, 5, 141: 

 1914. 6, 23. 



t Samec and Mayer : " Compt. rend.," 1921, 193, 321. 

 X Ling and Nanji : " J. Chem. Soc," 1923, 123, 2666. 

 § Ibid., 1925, 127, 630. 



