I08 THE PROTEINS OF THE WHEAT KERNEL. 



SUMMARY. 



The proteins of the wheat kernel are gliadin, insoluble in neutral aqueous 

 solutions, but distinguished from all the others by its ready solubility in 

 neutral 70 per cent alcohol ; glutenin, 1 a protein having a similar elementary 

 percentage composition to gliadin, soluble in very dilute acid and alkaline 

 solutions, but insoluble in dilute alcohol or neutral aqueous solutions and 

 yielding a wholly different proportion of decomposition products when boiled 

 with strong acids ; leucosin, an albumin-like protein, freely soluble in pure 

 water and coagulated by heating its solution to 50 to 60 ; a globulin similar 

 in composition and properties to many globulins found in other seeds, and 

 one or more proteoses which are present in very small quantity. It has 

 also been shown that the proteins obtained from the embryo of the wheat 

 are the globulin, albumin, and proteose above mentioned, and that! these 

 form nearly all of the protein substance of this part of the seed. It thus 

 appears that these three proteins are contained chiefly in the embryo, and 

 that gliadin and glutenin form nearly the whole of the proteins of the endo- 

 sperm, or over 80 per cent of the total protein matter of the seed. 



It is possible that a part of the albumin, globulin, and perhaps minute 

 quantities of the proteose are contained also in the endosperm, for these 

 proteins are always found in flour from which, in the milling process, the 

 embryo is very nearly completely separated. The uncertainty, however, 

 as to the completeness of this separation makes it questionable whether or 

 not the small amount of these proteins found in the best flour is not due to 

 the presence of more or less of the embryo that escaped separation in the 

 milling process. 



The flour of wheat differs from that of other seeds in forming a dough 

 when moistened with sufficient water, which, when washed with more water, 

 loses its starch, and finally yields a tough elastic mass, long known as wheat 

 gluten. This gluten contains the greater part of the protein matter of the 

 seed, together with a little starch, fat, lecithin, and phytocholesterin, and 

 possibly some carbohydrate substance or substances of as yet unknown char- 

 acter. These non-protein substances are probably not united with one another 

 in the gluten, but are mechanically mixed. The quantity of starch that 

 remains in the gluten depends on the thoroughness of the washing, while 

 the other substances owe their presence largely to their insolubility in water. 

 The chief constituents of the gluten are the two proteins, gliadin and glu- 

 tenin, the relative proportions of which vary with the variety of wheat from 



1 This is the protein which Ritthausen called "gluten-casein." 



