FEEDS 417 



change the nature of some of the ingredients. For example, certain 

 feeds tend to yield butterfat which varies in its melting point, but 

 efforts to increase the percentage of butterfat by feeding methods have 

 not met with commercial success. 



Examination of Table 16-6 on milk composition shows that the 

 total solids of cow's milk consist largely of butterfat, proteins, lactose, 

 and inorganic salts. Milk also contains carotene, vitamins A and D, 

 riboflavin, thiamine, and ascorbic acid. 



From a nutritional standpoint the proteins of milk are of great 

 importance since they contribute essential amino acids necessary 

 for normal health and growth. The proteins of milk are casein, 

 lactalbumin, and lactoglobulin. Casein is present in cow's milk in 

 the largest amount and represents that portion of the milk which 

 precipitates when milk becomes sour. This precipitate is called the 

 "curd" and is marketed as cottage cheese. 



Lactalbumin is a water-soluble protein which is coagulable by heat; 

 although it rarely occurs in excess of 0.5 per cent of the milk, it con- 

 stitutes about one-sixth of the total milk protein. Lactoglobulin is a 

 water-soluble protein which exists in normal milk in very small 

 amounts. 



Butterfat is a highly palatable mixture of glycerides of fatty acids. 

 The unique flavor of butterfat is attributed in part to the presence 

 of diacetyl (dimethylglyoxal) which is formed during the ripening of 

 the cream. In addition, branched-chain aldehydes of 5 to 10 carbon 

 atoms contribute to the flavor. The unique physical properties of 

 butterfat result from the types of fatty acids combined as glycerides. 

 Butterfat is characterized by the presence of a relatively large amount 

 of short-chain fatty acids such as butyric, caproic, caprylic, and capric 

 acids. 



From the viewpoint of nutrition it is unfortunate that the market 

 value of milk is based solely on its butterfat content. From an energy 

 standpoint butterfat has no advantage over several other edible fats 

 and oils. Butterfat does make important contributions to the vitamin 

 A content of the diet, but the carotene and the vitamin A contents 

 of butter are subject to wide seasonal variations. Vitamin A can be 

 obtained more economically from other natural foods, particularly 

 leafy vegetables, eggs, and whole milk. 



The chemistry of lactose has been discussed in Chapter 3. This 

 sugar is not hydrolyzed by adults as efficiently as other sugars, although 

 infants and young animals hydrolyze lactose to glucose and galactose 

 quite efficiently. Lactose forms lactic acid in the intestine, thereby 

 favoring the development of desirable types of acid-forming organisms 



