LIPIDES (fats and RELATED SUBSTANCES) 



85 



content of food. In 1919 Steenbock called attention to the occurrence 

 of vitamin A in close association with the yellow pigmentation of fats 

 and foods; for example, yellow corn was found to be rich in vitamin A, 

 while white corn was deficient in this vitamin. The same correlation 

 between vitamin and pigment was found with respect to carrots, squash, 



From Hawk and Bersjeim, Practical Phi/siolopical CheuiMnj. 

 Courtesy of P. Blakiston's Son & Co., Inc. 



Fig. 4-1. Crystals of beef fat. 



cabbage, and other vegetables. The work of von Euler, Moore, and 

 others has demonstrated that carotene of plants is the precursor of 

 vitamin A in the animal body. Carotene is transformed in the body, 

 apparently in the liver, from an intensely yellow pigment into an almost 

 colorless compound. This transformation is accompanied by changes in 

 structure and other properties of the pigment (see p. 207). 



In the pure state, fats have no taste, but by a curious anomaly natural 

 fats are the chief materials that give flavor to food. Food prepared with- 

 out the addition of fat is considered by many people unpalatable; liberal 

 additions of butter make food particularly appetizing. Butter owes its 

 taste largely to diacetyl (CH3 CO CO CH3) and acetylmethyl-carbinol 

 (CH3 CO CHOH CH3), compounds produced by bacteria in the ripen- 

 ing of tlie cream. 



The same condition obtains with respect to odor. When purified, fats 

 have no odor; yet natural fats frequently have marked odors. This 

 apparent contradiction is explained by the readiness with which fats 

 take up odors. The housewife carefully avoids i)utting onions and 

 butter together in the refrigerator. The absorption of odors by fats is 



