232 The Chenihtrii of tin StniH/f/i of W/irat Flour 



the same substance. It was therefore not possible, on the available 

 evidence, to explain the difference in the loaf-iiiakinti; qualities of different 

 flours by reference to their protein content. 



A valuable contribution to the study of the subject was made, when 

 Wood (3) resolved the conception of flour strength into two factors: 



1. Tii(> factor of strength which determines the shape of the loaf. 



^- J) ;• >j I! size ,, ,, 



The results obtained by this investigator justified the conclusion that 

 the capacity of a flour for giving off gas wjien incubated with yeast 

 and water is the factor which in the first instance determines the size 

 of the loaf. The latter depends not so much on the amount of sugar 

 present in the flour as such, but on the diastatic capacity of the flour, 

 which gives rise to continued sugar formation and consequently con- 

 tinued gas evolution in the dough. The same worker also showed that 

 the properties of gluten in regard to coherence and elasticita^ were 

 subject to considerable modification by the concentration of acid, alkali 

 or salt in the solution with which it was in contact, and he suggested 

 that these properties have an important bearing on the shape of the 

 loaf. A knowledge of the acidity and soluble .salt content of a flour should 

 therefore afford a clue to that factor of strength wliich decides whether 

 the flour will make a good-.shaped loaf. 



The information obtained in the investigation referred to above has 

 been applied with success in several pha.ses of the milling industry. The 

 view has long been held, however, by Professor Wood himself, that in 

 view of the improvement of tlie methods employed in protein research, 

 the question of the identity or non-identity of the corresponding gluten 

 proteins in weak and strong flours should be re-investigated. It is now 

 recognised that two proteins may be quantitatively identical with regard 

 to their amino-acid content and yet be two distinct proteins, by virtue 

 of dift'erences in the order of hnkage of the amino-acids within the protein 

 molecules. Such a case is furnished by the caseinogens of cow's and 

 sheep's milk. Though it is possible to show that these proteins are 

 distinct sub.stances(i), yet by the ordinary chemical methods of analysis 

 they are indistinguishable. 



It is clear, then, that any chemical method which is to be emplo3'ed 

 to decide on the identity or non-identity of related proteins must be 

 such as to take into account the pos.sibility of differences connected with 

 the order in which the constituents of the proteins are linked up within 

 the molecules. Such a method is the Racemisation Method, which has 

 been used recently in the investigation of the corresponding proteins of 



