I. WHY SODIUM CITRATE PREVENTS CURDLING 

 OF MILK BY RENNIN.*t 



ALFRED W. BOSWORTH and LUCIUS L. VAN SLYKE. 



SUMMARY. 



i. The addition of sodium citrate to milk in infant feeding is a 

 frequent practice in cases in which the use of normal milk results in 

 the formation of large lumps of tough indigestible curd in the stomach. 

 The favorable results attending such use of sodium citrate have never 

 been explained on the basis of actual investigation. 



2. Work previously done by the authors suggested a chemical 

 explanation of the observed facts and led them to test the matter 

 by an experimental study of the action of sodium citrate on milk. 



3. The addition of sodium citrate to normal milk increases the 

 amount of soluble calcium in the milk, this increase resulting from a 

 reaction between the calcium caseinate of the milk and sodium citrate, 

 by which is formed sodium caseinate (or calcium-sodium caseinate) 

 and calcium citrate. The reaction is reversible. 



4. The curdling of milk by rennin is delayed by the presence of 

 sodium citrate ; when there is added 0.400 gm. of sodium citrate per 

 100 c.c. of milk (equal to 1.7 grains per ounce), no curdling takes 

 place. 



5. The curd produced by rennin in the presence of small amounts 

 of sodium citrate (0.050 to 0.350 gm. per 100 c.c. or 0.20 to 1.5 grains 

 per ounce) increases in softness of consistency as the amount of 

 sodium citrate in the milk increases. 



6. The results of our work indicate that at the point at which 

 rennin fails to curdle milk we have in place of the calcium caseinate 

 of normal milk a double salt, calcium-sodium caseinate; this 

 double salt, when rennin is added, is changed to a calcium-sodium 

 paracaseinate which, owing to the presence of the sodium, is not 

 curdled. 



7. The practice of adding sodium citrate to milk at the rate of 1 

 to 2 grains of citrate per ounce of milk appears to have a satisfactory 

 chemical basis in the reaction between the sodium citrate and the 

 calcium caseinate of the milk. The amount added is governed by 

 the object in view, viz., whether it is desired to prevent curdling 

 or only modify the character of the curd in respect to softness. 



* Published also in the Am. Jour. Diseases of Children, 7 : 298-304. 

 t Reprint of part of Technical Bulletin No. 34, May; see p. 293. 



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