LIPIDS PRESENT IN MILK FAT 795 



cows, sheep, goats, and camels contains approximately 3% of this acid, 

 mature human milk fat contains only 0.4% of this 4-carbon acid, 492 or none 

 at all. 493 The milk fat of the mare most nearly approaches that of the 

 human in butyric acid content. 494 Another difference between human milk 

 fat and that of other species is its octadecadienoic acid content. This 

 value is considerably higher in human milk fat than in that of any animal 

 except the mare. 494 Human milk is also unique in containing a small 

 proportion of octadecatrienoic acid, although Eckstein 465 reported its pres- 

 ence in cow's milk fat. The milk fat of the Atlantic gray seal (Halichoerus 

 grypus) exhibits the greatest divergence in composition from the usual 

 fatty acid make-up of milk fats of any milk fat investigated. According to 

 Meara, 495 the total fat content of this milk is ten times the level of fat in the 

 milks of land animals. Only those fatty acids are present in the milk of 

 this seal which also occur in the blubber oil. However, this milk fat is 

 more saturated than is the body fat, particularly because of the higher pal- 

 mitic acid content. The opposite relationship between the saturation of 

 blubber fat and of milk fat obtains in the case of the blue whale (Balaenop- 

 tera musculus) . For an analysis of the composition of the milk fats of sev- 

 eral species, the reader is referred to pages 194 and 195 of Vol. I, The 

 Lipids. 



b. Colostrum vs. Mature Milk Fat. Marked variations in the composi- 

 tion of milk fat occur at different stages of lactation. The colostrum, 

 which is the first milk produced immediately after parturition, shows the 

 greatest variability from the mean average composition. Anantakrishnan 

 et al. m found that the composition of buffalo colostrum fat differed from 

 that of mature milk in having a lower content of butyric, myristic, and 

 palmitic acids, and an increased proportion of stearic and oleic acids. 

 The following figures (in per cent) were obtained for the composition of 

 colostrum milk fat and mature milk fat, respectively, of the buffalo: 

 butyric acid, 7.4, 12.1; caproic acid, 0.3, 0.7; caprylic acid, 1.3, 2.4; 

 capric acid, 1.5, 1.5; lauric acid, 1.7, 1.8; myristic acid, 9.1, 12.8; palmitic 

 acid, 19.5, 28.2; stearic acid, 15.9, 11.5; arachidic acid, 0.9, 0.7; and total 

 saturated acids, 57.6, 71.7. In the group of unsaturated acids, the follow- 

 ing differences in composition were noted between colostrum and mature 

 butterfat: decenoic acid, 0.1, 0.1; dodecenoic acid, 0.1, 0.1; tetradecenoic 



492 A. R. Baldwin and H. E. Longenecker, J. Biol. Chem., 154, 255-265 (1944). 



493 T. P. Hilditch and M. L. Meara, Biochem. J., 38, 29-34 (1944). 



494 T. P. Hilditch and H. Jasperson, Biochem. J., 38, 443-447 (1944). 



495 M. L. Meara, Biochem. J., 51, 190-193 (1952). 



496 C. P. Anantakrishnan, V. R. B. Rao, T. M. Paul, and M. C. Rangaswamy, J. Biol. 

 Chem., 166, 31-33 (1946). 



