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Electrolytes and Colloids. — The Physical State of Gluten. 

 By Prof. T. B. Wood and W. B. Hardy, F.R.S. 



(Received October 24,— Eead December 10, 1908.) 



G-luten, as ordinarily prepared by washing wheat flour in tap water, forms 

 a coherent stringy mass insoluble in water. It consists essentially of 

 a mixture of two proteins, gliadin and glutenin, but even when very 

 thoroughly washed it always includes some starch. Gliadin, which forms 

 rather more than half of the total protein, is soluble in dilute alcohol, and 

 gives to the gluten its peculiar physical properties. 



The power which dough possesses of retaining the gas formed during 

 fermentation is due to the tenacity and ductility of gluten.* Therefore, 

 the property of forming a light and well-shaped loaf, which is so variable 

 a feature of different flours, is determined by the amount and the physical 

 state of the contained gluten. 



The physical state of gluten, like that of other colloids, is conditioned 

 by the electrolytes which are present. Gluten washed out of flour with 

 distilled water obviously is more friable and less tenacious than gluten 

 washed out with tap water which contains salts. It is this influence of 

 electrolytes upon the physical state of gluten which we propose to discuss. 



Gluten is peculiarly sensitive to low concentrations of acid or alkali. 

 A tenacious ductile mass suspended in a large volume of, for instance, 

 O'OOOl normal acid, begins almost at once to show signs of disintegration, 

 and is at once dispersed by slight movement to form a stable opaque 

 colloidal solution or hydrosol. 



Action of Acids. — This action was investigated quantitatively by 

 suspending a small mass of gluten on a bent glass rod in a beaker 

 containing 120 c.c. of a solution of acid of known strength, and noting the 

 concentration at which cohesion was so far reduced as to allow the protein 

 to fall off the rod and disperse in a cloudy " solution." It was found that 

 while very dilute acid causes dispersion, a solution of a strong acid above, 

 a certain concentration maintains the cohesion. Gluten, therefore, is 

 coherent in distilled water, and in strong acids above a certain critical 

 concentration. A weak acid, such as acetic acid, brings about dispersion up 

 to as high as twice normal, the highest concentration tried. Inspection of 

 a series of beakers with concentrations of any strong acid from zero to the 

 critical point makes it clear that, starting from the lowest concentration, 

 * Wood, ' Journ. Agric. Sci.,' vol. 2, part 2, p. 139, and part 3, p. 267. 



