CHAPTER V. 



SOLUBILITY OF VEGETABLE PROTEINS. 

 A. Solubility in Water. 



ALL seeds, when ground fine and treated with water, yield extracts 

 which in most cases contain only a small quantity of protein substance. 

 Some of this consists of proteose and albumin, soluble in pure water ; 

 some may be globulin, dissolved in the dilute saline solution formed by 

 the soluble mineral constituents of the seed ; and some may be protein, 

 insoluble in water alone, but dissolved by the acids extracted from the 

 seeds. 



From some of the leguminous and other seeds, when freshly 

 ground, water extracts a considerable quantity of protein which, after 

 a time, begins to separate from solution in consequence of a develop- 

 ment of acid in the extract. This separation can also be effected by 

 adding a small quantity of acid. We have just shown, page 28, that 

 there are proteins, e.g., legumin, which in the free state are soluble in 

 water, but when combined with a small amount of acid, as a protein 

 salt, are insoluble in water, but soluble in neutral saline solutions. 



It is, consequently, necessary to consider carefully the conditions 

 under which the dissolved protein exists in its solution before definite 

 conclusions can be reached as to its true solubility. 



Most, perhaps all, seeds, when extracted with water, yield a small 

 proportion of proteose which may either be a constituent of the seed 

 or be derived from the other proteins by the action of enzymes. Be- 

 sides this proteose a small amount of protein is nearly always present 

 which appears to have the properties of a true albumin. Whether 

 this latter is actually an albumin soluble in pure water is difficult to 

 determine definitely. 



Leucosin (366) from wheat flour is the only critically studied vege- 

 table albumin which in the free state, as well as when combined with 

 acids, is soluble in water. 



It is generally assumed, and seems to be highly probable, that 

 most seeds contain a small proportion of similar albumins, but few are 

 known in which such occur in any considerable quantity. 



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