THE ISOELECTRIC POINTS OF THE PROTEINS IN 

 CERTAIN VEGETABLE JUICES. 



By EDWIN J. COHN,* JOSEPH GROSS, and OMER C. JOHNSON. 



{From the Earriman Research Laboratory, Roosevelt Hospital, New York, in 

 , Collaboration with the Section of Food and Nutrition, 



Medical Department, U. S. Army.) 



(Received for publication, August 21, 1919.) 



The preparation 'n the dry condition of systems rich in protein 

 has assumed new importance in the practise of dehydrating vegetables 

 and meats. Until recently the removal of water and the preservation 

 of the original appearance of the foodstuffs have been considered the 

 most important criteria for success in the operation. But accepta- 

 bility of the dehydrated product has varied largely. In certain 

 instances vegetables have lost important nutritional quaHties upon 

 dehydration or shortly thereafter. Others have been slow to reab- 

 sorb water. Occasionally dehydrated material has spoiled. 



Information regarding the nature of the proteins in such systems, 

 should exp.a n, in part, the causes of variation, set up criteria for 

 change upon dehydration, and lead gradually to the perfection of 

 • processes. 



With this in \dew the characteristics of the proteins in the juices 

 of the potato, of the carrot, and of the tomato have been studied. 

 Their isoe ectric points and their solubility at different hydrogen ion 

 concentrations have been determined. The acidity of the juices of 

 these vegetables together with this information suggests the state 

 in which the proteins exist in nature. 



The Significance of the Isoelectric Point. 



The classification of simple proteins depends upon their solubihty 

 in water containing different concentrations of inorganic salts (albu- 

 mins from globuhns) , different concentrations of hydrogen ions (albu- 

 mins and globuHns f rom glutelins) , or different concentrations of alcohol 



* Lieutenant, Sanitary Corps, U. S. Army. 



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