STARCH 149 



Preparation of Starch. 



The method of preparation varies according to the source 

 employed. From wheat flour it may be obtained by stirring 

 up this material thoroughly with water, and allowing the mix- 

 ture to stand until the gluten contained in the flour undergoes 

 fermentation, when it dissolves and may be removed by wash- 

 ing. On a small scale the separation is most conveniently 

 effected by kneading some flour in a muslin bag which is held 

 under a stream of water. The starch granules are hereby 

 washed through the muslin, while the gluten remains behind 

 in the bag as a sticky grey mass. 



Starch may also be obtained from potatoes by macerating 

 them with water and separating the non-starchy material from 

 the starch by filtration. The starch is then allowed to settle at 

 the bottom of the water, when it is collected and dried. 



Purification. 



Malfitano and Moschkoff * give the following method for 

 the purification of starch : A I per cent colloidal solution of 

 starch is frozen and then allowed to melt. When melted, most 

 of the starch is deposited in a floccular precipitate, whilst the 

 clear liquid contains some starch and the greater part of the 

 mineral impurities. On repeating the operation four or five 

 times, the purified product yields less than -02 per cent of ash. 

 Even the purest starch yields on incineration a small amount 

 of ash constituents chiefly of phosphates which were in organic 

 combination with the material (see Amylopectin, p. 152). 

 In addition to phosphates, varying quantities of silica are 

 found in the ash, the amount depending on the source from 

 which the starch was prepared. Silica is not a true constituent 

 of the starch proper, but is associated with another substance, 

 known as amylohemicellulose,t which occurs in greater 

 quantities in some starches than in others, notably in the 

 starches of barley, wheat, rice, tapioca, maize, and sago,| 



* Malfitano and Moschkoff : " Compt. rend.," 1910, 151, 817. 

 t Ling and Nanji : " J. Chem. Soc," 1923, 123, 2672 ; 1925, 127, 652. 

 X Clayson and Schryver : " Biochem. Journ.," 1923, 17, 493 ; Schryver 

 and Thomas : id., 497. 



