48 Chemical Properties of Wheaten Flour. 



higher proportion of gliadin. The subject evidently demands 

 further study. 



Proteins of Flour. 



As already indicated, wheat contains more than one protein. 

 Gliadin and glutenin make up about 90 per cent, of the total 

 protein matter of the seed ; this in addition contains leucosin, 

 a so-called albumen, which is freely soluble in water and 

 coagulates when the solution is heated. In gluten the gliadin 

 acts as the sticky binding substance, whilst the glutenin serves to 

 fill up the network of gliadin threads. 



These two proteins were thought at one time to have a 

 common origin or to be derived from one another when flour is 

 wetted. Osborne, who has studied the products of their com- 

 plete hydrolysis, finds that gliadin differs sharply from glutenin 

 in yielding no glycine and no lysine ; it also gives nearly twice as 

 much proline as glutenin. 



Both gliadin and glutenin, which yield 37 and 23 per cent, of 

 glutamic acid respectively, differ greatly from leucosin, which 

 gives only 6 per cent, of this acid. They both give rise to con- 

 siderable quantities of ammonia, whereas leucosin yields but little 

 ammonia. 



The substances mentioned as decomposition products of gliadin 

 and glutenin all belong to the "amino acids," which modern 

 research has shown to make up the greater portion of the protein 

 molecule. 



T. B. Wood has carried out experiments which indicate that 

 gliadin derived either from strong or weak wheats is the same 

 in each case. Osborne's very careful researches all show that the 

 proteins of wheat are of constant composition independent of 

 their origin. 



To sum up : whereas, broadly speaking, strength must be 

 associated with the total quantity of gluten or nitrogen in a 

 flour, yet it is the physical properties of gluten, rather than the 

 amount, which determine the behaviour of the flour in bread- 

 making. 



Sugar. 



The distention of the loaf is due to the gas formed during 

 panary fermentation from sugar. The amount of sugar actually 

 present in flour would not suffice to give the necessary volume 

 of gas, but it is supplemented by sugar produced from the starch 

 of the flour. The formation of sugar is effected by the agency 

 of a diastatic enzyme ; it begins directly the flour is wetted 

 and continues throughout fermentation until the loaf is baked. 

 In general, therefore, the presence of more or less sugar in a 

 flour is unimportant, and the percentage shows no relationship 

 with the volume of the loaf. 



