LIPIDS PRESENT IN MILK FAT 791 



fats to pass through the phospholipid stage. Lovern and Morton 44 demon- 

 strated the presence of free fatty acids in the intestinal mucosa. 



14. Lipids Present in Milk Fat 



CO The Composition of Milk Fat 



a. Fatty Acids in Milk Fat. In most species of animals, the composition 

 of the milk fat differs from that of the depot fat. Although there are minor 

 differences in the fatty acid patterns in milks obtained from different types 

 of animals, by and large milk fats are characterized rather by their similari- 

 ties. Thus, myristic and palmitic acids are consistently present in mature 

 milk from several species of animals, within the relatively narrow ranges of 

 7 to 12% and 22 to 32%, respectively. A considerable uniformity like- 

 wise obtains in the oleic acid content, which usually ranges between 28 and 

 41% in the different milks. The most characteristic components in milk 

 fat are the volatile acids, which comprise 7% of the total fatty acids, al- 

 though values more than twice this figure have been recorded for milk 

 fats from at least one species of animal. 



The first comprehensive analysis of butterfat was that of Bosworth and 

 Brown. 463 These investigators reported the presence of the monoethenoid 

 acids with an even number of carbons from do to d 4 . Hilditch and Longe- 

 necker 464 have shown that the double bond is present in the 9-10 position; 

 this can be interpreted to mean that these acids originated from oleic acid 

 by combined oxidation and reduction. 



Linoleic acid is another acid which has been demonstrated in butterfat. 

 Although Bosworth and Brown 463 failed to detect the presence of this acid 

 in butterfat, Eckstein 465 found that it was present to the extent of 0.17 to 

 0.25% in cow's butter. Linolenic acid was also demonstrated in this fat in 

 amounts of 0.07 to 0. 17%. Using a new spectrophotometry method for the 

 determination of the dienoic and trienoic acids, Schaffer and Holm 466 ob- 

 tained values of 2.62 to 2.71% for linoleic acid in summer milk fat, while 

 octadecatrienoic acid values varied between 0.77 and 1.17%. These re- 

 sults are within the range of total essential acid content for butters reported 

 by Deuel et al., m who employed a new bioassay method for the determina- 

 tion. It is probable that the divergent results concerning the presence and 



463 A. W. Bosworth and J. B. Brown, J. Biol. Chem., 103, 115-134 (1933). 



464 T. P. Hilditch and H. E. Longenecker, J. Biol. Chem., 122, 497-506 (1938). 

 466 H. C. Eckstein, J. Biol. Chem., 103, 135-140 (1933). 



466 P. S. Schaffer and G. E. Holm, J. Dairy Sci., 33, 865-869 (1950). 



467 H. J. Deuel, Jr., S. M. Greenberg, L. Anisfeld, and D. Melnick, /. Nutrition, 45. 

 535-550(1951). 



