8 MILK AND DAIRY PRODUCTS. PART 



The most characteristic property of casein is that of curdling 

 when acted upon by rennet in the presence of a sufficient 

 quantity of a soluble lime salt. In the absence of lime salts 

 casein is not coagulated by rennet. The casein does, however, 

 undergo a change when acted upon by rennet in the absence 

 of lime, for if lime salts are afterwards added a coagulum is 

 obtained, which possesses exactly the same properties as those 

 of the curd obtained in the normal way. Rennet, therefore, 

 acts upon casein in the absence of lime salts, but the latter 

 are necessary for the precipitation of the curd. 



Hammarsten, who was the first to demonstrate these con- 

 ditions, 1 is also the original proposer of a theory regarding the 

 coagulation of milk by rennet, which is, briefly, the following : 

 Under the action of the rennet the casein is split up, and, 

 gives on the one hand a body which is only slightly soluble 

 and which stands in very close relation to casein ; this he calls 

 paracasein, and it is the main product of the cleavage. On 

 the other hand, there remains in solution a small quantity of an 

 easily soluble albumin-like substance which is poorer in carbon 

 and nitrogen than the paracasein and is named whey-albumin. 



Casein can be separated from milk by means of acids or certain 

 solid salts, e.g. common salt. The simplest method for obtaining 

 the casein from milk is to dilute it with four times its volume 

 of water and then add acetic acid up to 1 part per 1000. The 

 precipitated casein is then repeatedly dissolved in water with 

 the help of a little alkali, reprecipitated with acetic acid, and 

 carefully washed. Final ly, the casein is freed from traces of fat 

 by treatment with alcohol and ether. 



Lacto-albumin was first prepared in a pure state from milk 

 by Sebelien, 2 who gives its composition as : 



C 52-19 per cent. 



H 7-18 



N 15-77 



8 1-73 



23-13 



100-00 per cent. 



Its properties resemble those of the albumins in general, but 

 it is distinguished from serum-albumin by its considerably 



1 Maly's Jdhresber. Vols. II and IV ; also Hammarsten, " Zur Kenntnis cles 

 Kaseins mid der Wirkung des Labferments," Nova Acta Hey. Soc. Scienl., 

 Upsal., 1877. ' 2 Zeitnclirift fiir phytiioloy. Chem., Vol. IX. 



