146 PROTEINS AND AMINO-ACIDS [ch. 



(c) Extraction of gliadin. Take 100 gms. of flour (or ground wheat) and add 

 125 c.c. of 70 % alcohol. Warm on a water- bath and filter. Repeat the process with 

 another 125 c.c. of alcohol. Evaporate the filtrates, which contain gliadin, on a 

 water-bath (or better distil off" the alcohol in vacuo). When reduced to about half its 

 bulk, take a little of the filtrate and filter. Divide this filtrate into two parts in test- 

 tubes. To one add water : to the other absolute alcohol. A white precipitate of 

 gliadin is formed in each case, since it is insoluble in both water and strong alcohol, 

 though soluble in dilute alcohol. The remainder of the gliadin extract is evaporated 

 almost to dryness, and then poured slowly into a large volume of distilled water. 

 A milky precipitate of gliadin is formed which may be made to settle by adding a 

 little solid sodium chloride and stirring. Filter off the gliadin and dissolve in 10 ^Jq 

 acetic acid. With the solution make the tests for protein [Expt. 127, (a)-(o?)J. 



{d) Extraction of glutenin. Take 100 gms. of flour, make it into a firm dough 

 with water in an evaporating dish and allow this to stand for half an hour. The 

 dough consists of gluten (gliadin and glutenin) to which the starch adheres. Then 

 put the dough into a piece of fine muslin and knead and wash thoroughly in a 

 stream of water until all the starch is removed. Collect some of the washings in a 

 beaker and to this suspension of starch add a few drops of iodine solution. It will 

 turn a deep blue-black colour. When the starch is completely washed away, an 

 elastic rubbery mass of gluten will remain. 



Take about 10 gms. of the gluten, divide it into small pieces and heat it in a 

 flask on a water-bath with small quantities of 70 % alcohol until the extract gives 

 no, or very little, milkiness (due to gliadin) on pouring into water. Decant ofl" the 

 alcohol from the residue of the glutenin, as it can only be filtered with difiiculty. 

 Dissolve the glutenin in 0*2 % caustic potash solution. Neutralize a portion of this 

 solution with deci-normal sulphuric acid, drop by drop. A precipitate of glutenin is 

 formed. Test the remainder for proteins [Expt. 127 {a)-{d)'\. 



Expt. 136. To demonstrate the fact that gluten formation depends on the presence 

 of gliadin. Repeat Expt. 135 {d) with flour that has been extracted with 70 o/q alcohol 

 for two or three days. (The alcohol is allowed to stand on the flour in the cold. It 

 is then poured ofl", and more added, and the process repeated. The flour is now dried 

 again, first in air, then in the steam-oven and finally is ground in a mortar.) No gluten 

 will be formed on account of the absence of gliadin. 



In the Barley (Hordeum vulgare) grain, small percentages of an 

 albumin, apparently identical with leucosin, and of a globulin, barley 

 edestin, are present, together with some proteose. The main protein is 

 a prolamin, hordein, very similar to, but not identical with, gliadin. 

 There is no well-defined glutelin (Osborne, 11). 



In the Rye (Secale cereale) grain there are small percentages of 

 proteose, and of leucosin and edestin. The greater part of the protein 

 is gliadin, said to be identical with that in wheat. 



In the Maize {Zea Mays) grain there is apparently no true albumin, 

 though there is some proteose. There are small quantities of globulin, 

 but the greater part of the protein is a prolamin, termed zein, and a 

 glutenin (Osborne, 12). 



