452 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Globulin and Albumin from Cereals. 



These proteins are present only in small quantities in the flotr, but the 

 germ contains up to 10 per cent, of coagulable proteins. 



The germ is extracted with water ; sufficient salt is present to dissolve 

 some of the globulin, or the germ is extracted with 10 per cent, salt solution. 

 The proteins are precipitated by saturating the extract with ammonium 

 sulphate. The precipitate is dissolved in water or salt solution and dialysed. 

 The globulin is precipitated and purified by again dissolving and dialysing. 

 The albumin (leucosin of wheat) in the solution is obtained by heat coagula- 

 tion. The two proteins have the general properties of globulins and albumins. 



GLIADINS AND GLUTELINS. 



The chief constituents of the seeds of cereals are starch and protein. 

 Small quantities of fat and salts are also present. 



The chief protein constituents form a distinct group which is not 

 represented in other plants nor in animals. They are therefore known 

 as gliadins and glutelins. The percentage composition of the protein 

 matter of the flour of cereals is the following : 



The mixture of glutelin and gliadin in roughly equal proportions 

 is known as gluten. 



Gluten. 



About 20 gm. of flour is made into a dough with 8-10 c.c. of 

 water and the dough is allowed to stand for 15-60 minutes. It is 

 washed by kneading in a piece of muslin under running water. The 

 washing is continued until no more starch can be removed. The re- 

 mainder has a sticky elastic consistency and is of a grey to pale yellow 

 colour. When it is dried the gluten forms a brittle mass like glue and 

 is yellow-brown in colour. It is contaminated with the fat of the grain 

 and some starch. 



The formation of gluten is due to the gliadin, which makes a 

 sticky mass with water and binds together the particles of glutelin. 

 The elastic properties of gluten depend mainly upon the proportion 

 of salts present in the flour, especially phosphates. Rye does not 

 form gluten but contains a large proportion of a gummy polysaccharide. 



