PHYSICAL PROPERTIES OF MILK 85 



pigments of the fat at this time are identical with the normal 

 pigments of the fat. Their increase at this time is probably 

 due to the physiological conditions surrounding the secretion 

 of the milk of the freshening animal. 



THE YELLOW PIGMENT OF MILK WHEY 



In a similar way Palmer and Cooledge studied the yellow color 

 of milk whey. Since the chief color of milk is due to the carotin 

 in the fat, the pigment in the whey may be considered as the 

 secondary or minor pigment of milk. It is this pigment which 

 gives to whey its greenish-yellow color. They regard this minor 

 pigment to be " lactochrome " which was formerly believed to 

 be chiefly responsible for the yellow color of milk and butter-fat. 

 Studies of the chemical properties of lactochrome showed 

 "its very close relationship to urochrome, the specific pigment 

 of normal urine, the general characteristics of the two pigments 

 being identical." (Pages 85-91 from Palmer and Cooledge.) 

 Factors influencing the color of milk whey. 



During the course of the investigations of the milk whey pig- 

 ment a wide variation in the color of the whey from the milk of 

 different animals was noticed. This was especially evident 

 when the color of the whey from sheep's milk was compared with 

 the color of the whey from cow's milk, and was also. often evident 

 when merely observing two samples of freshly prepared whey 

 from the milk of two different cows. In order to establish a 

 better standard of comparison and study the factors that might 

 be influencing the amount of lactochrome in the milk the follow- 

 ing procedure was adopted : 



Freshly drawn milk was run through a cream separator at a 

 uniform speed and the casein precipitated from the skim milk 

 with the smallest amount of 10 per cent acetic acid necessary to 

 cause a clear coagulation. A portion of the cloudy yellow fil- 

 trate was then boiled for a few minutes to bring down the coagu- 



