Chemical Properties of Wheaten Flour. 47 



content and afford no absolute measure of strength. Equally 

 unsatisfactory is the determination of nitrogen in the dry gluten. 



No doubt future work will involve the study of the forms *in 

 which nitrogen is present. 



All measurements hitherto made indicate that strength depends 

 on the quality rather than on the quantity of the proteins in flour. 

 However, the protein content, when judging normal flours, is 

 undoubtedly the best single measure of strength. 



Quality of Gluten. 



No satisfactory chemical data by which this can be gauged 

 have been obtained. Measurements have been made, for example, 

 of the power of expansion when a definite weight of gluten is 

 heated in metallic cylinders to a definite temperature. Of greater 

 significance is the water-holding capacity or hydration ratio as 

 measured by the ratio of the wet gluten immediately after ex- 

 traction under carefully standardised conditions to its weight after 

 drying. The ratio is on the average about 3:1; that is, gluten 

 carries about twice its weight of water. No generally accepted 

 regularity has been demonstrated, but in gluten from strong flours 

 the ratio is as low as 2*6, whilst in that from very weak flours 

 the ratio is often above 3. As Mr. Hardy points out in the fol- 

 lowing paper, this ratio is to be associated with the mineral 

 content of the flour. 



Emphasis must be laid on the fact that the method of deter- 

 mining gluten by washing is purely empirical and requires careful 

 standardisation before comparative results can be obtained. 

 Measurements of gluten at the best are but a rough-and-ready 

 guide to more exact determinations ; they have the advantage 

 that they can be made quickly without special apparatus. 



Gliadin Ratio. 



Crude gluten consists mainly of two proteins : gliadin, soluble 

 in alcohol, and glutenin, soluble in very dilute alkalis or acids. 

 It has been suggested that the ratio of gliadin to glutenin, or the 

 ratio of gliadin to the total protein in the flour, influences the 

 quality of gluten and affords a measure of strength. Girard and 

 Fleurent suggested the proper proportion of gliadin to be 75 per 

 cent, of the gluten. Snyder fixed the ideal ratio at 65 per cent., 

 but experience has not supported these views ; the gliadin ratio 

 is erratic and apparently of little value for diagnostic purposes. 

 A. D. Hall has adversely criticised the determination of the per- 

 centage of gliadin as an indication of strength ; F. T. Shutt 

 considers it to be more valuable, and suggests there is an indica- 

 tion of a relationship between the maturity of the grain and the 

 gliadin - content. The more fully ripened wheat contains the 



D 2 



