CAROTIN, THE PRINCIPAL \ELLOW PIGMENT OF MILK FAT 383 



DISCUSSION OF RESULTS. 



It was the primary object of this investigation to classify the 

 natural yellow pigment of milk fat both as an individual and also 

 in relation to the two well-known yellow classes of plant pigments, car- 

 tin and xanthophylls, whose general properties have often been observed 

 to be closely related to various yellow pigments of so-called animal 

 origin. 



Basing the study upon a number of well-defined, characteristic 

 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 characteristics 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 hitherto been considered to be 

 in the animal body is in reality merely the carotin and xanthophylls 

 of the food, which are absorbed by the body and subsequently secreted 

 in the milk fat. Numerous feeding experiments show that when the 

 food is deficient in carotin and xanthophylls for a period of time, the 

 milk fat slowly decreases in color and eventually approaches a color- 

 less condition. The experiments also show that when foods rich in 

 carotin and xanthophylls are given to a cow whose milk fat is deficient 

 in lipochrome, the color of the milk fat at once increases in propor- 

 tion to the amount of pigments fed. This is true regardless of whether 

 the carotins and xanthophylls are associated with chlorophyll as in 

 green feeds, or whether chlorophyll is completely absent and xan- 

 thophylls almost so, as in carrots. 



The experiments show in addition that small amounts of carotin, 

 such as are present in the oil of cottonseed meal have apparently no 

 effect on the color of the butter fat. It is not clear, however, whether 

 this is due to the smallness of the amount of carotin or to the state 

 in which it exists in the food, i. e., dissolved in oil. There is some 

 evidence on both sides. Mendel and Daniels * have recently found 



1. Jour. Biol. Chem. 13, No. 1, p. 72 (1912). 



