PHYSICAL PROPERTIES OF MILK 75 



THE YELLOW COLOR OF MILK AND MILK-FAT 



The natural yellow color of milk and its products, especially 

 butter, is of considerable commercial value because the public 

 regards this character as an indication of quality. The sub- 

 stance which imparts the yellow color has been given the name 

 of " lactochrome " by some writers, but little has been known of 

 its real nature. Because of the fact that milk and butter are the 

 most highly colored during the early part of the summer when 

 cows are feeding on green grass, it has been assumed that there 

 is some relation between the yellow color of milk and the chloro- 

 phyll of green plants. Recently, Palmer and Eckles have studied 

 the yellow color of milk-fat and Palmer and Cooledge the yellow 

 color of whey. 



Palmer and Eckles 1 found that the natural yellow pigment of 

 milk-fat is due to the presence of two classes of yellow pigments 

 which are common in green plants known as carotin 2 and 

 xanthophylls. They say : 



" Basing the study upon a number of well-defined, characteris- 

 tic physical and chemical properties of carotin and xanthophylls, 

 it has been shown that the principal pigment of milk-fat is a 

 member of the fast widening group of hydrocarbon pigments, 

 the carotin of green plants. In addition it has been shown that 

 the milk-fat carotin nearly always has associated with it one 

 or more minor constituents whose general properties and charac- 

 teristics are identical with the xanthophyll group of pigments. 

 Two and possibly three xanthophyll constituents were found in 

 one sample of high-colored butter-fat. 



"In addition to the establishment of a chemical relation 

 between carotin and xanthophylls and the yellow lipochrome 

 of milk-fat, it has been possible to demonstrate a much more 

 significant fact, namely that this lipochrome whose origin has 



1 Missouri Research Bui. 10. 



2 So named from the yellow color of carrots. 



