GENERAL CHEMISTRY OF MILK 97 



2. The chemical part of the process is retarded by gradual 

 destruction of the rennet by temperatures above 41 C., free 

 hydroxyl ions, inactivation through antirennin, change of the 

 casein by heating above 80 C., and the presence of formalin. 



3. The physical part of the process is accelerated by high 

 temperature, free hydrogen ions and neutral salts up to a certain 

 concentration, especially the salts of alkaline earths. 



4. The physical part of the process is retarded by diminished 

 concentration of the salts of alkaline earths, which are precipi- 

 tated by heat, and the increased concentration of neutral salts. 

 Possibly alkalies also act in this direction. 



LACTALBUMIN 



Lactalbumin is similar to serum albumin and can be prepared 

 from milk by the following methods: 



1. Milk is saturated witrrMgSO 4 and filtered. To the filtrate 

 are added a few drops of a 0.25 per cent, acetic acid. The pre- 

 cipitate is gathered and redissolved and the solution neutralized. 

 By repeated precipitation with MgSO 4 remnants of casein and 

 globulin are removed and the solution is dialyzed until MgSO 4 

 has disappeared. The albumin is then precipitated with alcohol. 

 Finally the precipitate is dried at low temperature. 



2. Milk is filtered through a porcelain filter and the albumin 

 precipitated from the filtrate by saturation with ammonium sul- 

 phate. The precipitate is dialyzed, reprecipitated with alcohol 

 and dried. Lactalbumin is crystallizable; if the solution of lac- 

 talbumin is saturated with MgSO 4 , this solution diluted with an 

 equal volume of water, and then acetic acid added until a per- 

 manent turbidity appears, crystals will form on standing. Crys- 

 tallization is aided by occasional gentle agitation. The form of 

 the crystals is the same as that of egg-albumen and serum albu- 

 min, but its rotation is different (Mathews). 



When prepared by one of the above methods, lactalbumin is 

 a tasteless white powder, easily soluble in water. Lactalbumin 

 contains no phosphorus, but twice as much sulphur as casein. 

 Elementary analysis gives the following composition (Sebelein) : 



C. = 52.10, H. = 7.18, N. = 15.77, S. = 1,73, O. = 23.13 



It is soluble in saturated solutions of NaCl and MgS04, but 

 is precipitated by a saturated solution of (NH 4 ) 2 SO 4 . It is pre- 

 cipitated from a saturated solution of MgSO 4 by addition of acid, 

 but is redissolved if the acid is neutralized. Rupp states that 

 there is no albumin coagulated at 62.8 C. if this temperature be 

 maintained for thirty minutes. Under the same conditions at 



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