ii8 Indianapolis Biochcmical Meeting: Ahstracts [Sept 



The Influence of Sodium Chlorid on the Precipitability of 

 Casein by Acetic Acid and its Bearing on the Parti- 

 tion of Nitrogen in Butter 



WILLIAM N. BERG 



(Dairy Division Research Laboratories, Bureau of Animal In- 



diistry, Washington, D. C). 



Acetic acid as a precipitant for casein in milk, buttermilk, etc., 

 has been the subject of many careful researches. While the dif- 

 ferent methods of precipitation may differ in certain details, they 

 are alike in principle. The milk, or other casein-containing fluid, 

 is diluted to a convenient volume and acetic acid is added in amount 

 sufficient to flocculate the casein completely. Thus, if 200 c.c. of 

 buttermilk (or milk) are diluted to nearly 500 c.c, the addition of 

 5 c.^. of IG per Cent, acetic acid will flocculate the casein. Such 

 a Suspension of flocculent casein Alters rapidly and gives a clear 

 filtrate. If to a second 200 c.c. portion of the same sample of 

 buttermilk 36 grams of sodium chlorid are added before diluting 

 with water, the addition of 5 c.c. of 10 per cent acetic acid does 

 not flocculate the casein. The sodium chlorid very profoundly 

 influences the precipitability of the casein because none is pre- 

 cipitated under these conditions. Not until three or four times the 

 usual amount of 10 per cent. acetic acid is added (15-20 c.c.) does 

 the casein flocculate, permitting rapid filtration. 



The above described effect of the sodium chlorid was noticed 

 in the course of a study of the possible proteolytic changes taking 

 place in cold storage butter. Butter usually contains casein ( i per 

 cent.), sodium chlorid (3 per cent.) and water (16 per cent.) in 

 such proportions that when butter is melted, allowed to stand, and 

 the clear supernatant fat poured off, a thick, viscid fluid (curd 

 Solution) remains, which is mixed with several per cent. of fat and 

 contains approximately 6 per cent. of casein and other nitrogenous 

 substances, and 20 per cent of sodium chlorid. 



If the curd Solution obtained from butter be treated with water 

 and acetic acid as if it were so much milk, flocculation does not 



