Milk fat bovine

In testing for authenticity of bovine milk fat (Luf, 1988a Younes and Soliman, 1987) the first test should be for the presence of plant sterols, this indicating the presence or absence of vegetable oils. This can be carried out by similar 

Fatty acid analysis of a fat is nowadays a relatively routine analytical operation. After methylation of the fat using reaction with boron trifluoride/methanol, boron trichloride/methanol, methanolic hydrogen chloride solution, diazomethane or, if free fatty acids are not present, alkaline catalysts such as sodium methoxide/methanol, the prepared methyl esters are then analysed by GC on a polar column such as CpSil 88, BPX70 or SP2340. The high polarity of the column is necessary to separate the saturated and unsaturated fatty acids fully. The fatty acid composition of a milk fat sample is thus relatively easily obtained, and was therefore one of the first techniques investigated for authentication purposes. 

Milk fat does have a very characteristic fatty acid composition, and contains about 15 major fatty acids and several hundred minor fatty acids (Gunstone etal., 1994 Hettinga, 1996). One might think that this would mean that authentication would be relatively easy from just the fatty acid composition. However the fatty acid composition is not just complicated, it is also very variable. Early surveys showed this variability (Hilditch and Williams, 1964 Hallabo and El-Nikeety, 1987) and some of the reasons for this variability were soon evaluated (Hilditch and Williams, 1964). 

Other factors are also claimed to affect the fatty acids in milk. Cattle low in copper are reported to give milk higher in conjugated linolenic acid (Sol-Morales 

A summary of the ranges of major fatty acids ( 1%) that have been found in bovine milk fats is given in Table 5.3. This includes values obtained from 

---

Table 11.4 Averaged composition of the major fatty acids in bovine milk fat (adapted from Jensen, 2000 297).

Unsaturated fatty acids may occur as cis or trans isomers trans isomers, which have higher melting points than the corresponding cis isomers, are considered to be nutritionally undesirable. Bovine milk fat contains a low level (5%) of trans fatty acids in comparison with chemically hydrogenated (hardened) vegetable oils, in which the value may be 50% due to non-stereospecific hydrogenation. 

Bovine milk fat contains low concentrations of keto and hydroxy acids (each at c. 0.3% of total fatty acids). The keto acids may have the carbonyl group (C=0) at various positions. The 3-keto acids give rise to methyl O... 

Figure 3.6 Seasonal changes in the iodine number of Irish bovine milk fat (from Cullinane et al., 1984a).

Figure 3.9 Sources of the fatty acids in bovine milk fat TG, triglyceride (from Hawke and Taylor, 1995).

As the chain length increases up to C,6 0, an increasing proportion is esterified at the sn-2 position this is more marked for human than for bovine milk fat, especially in the case of palmitic acid (C,6 0). 

Table 3.10 Composition of bovine milk fat globule membranes...

Table 3.11 Structures of glycosphingolipids of bovine milk fat globule membrane ...

Table 3.12 Enzymatic activities detected in bovine milk fat globule membrane preparations...

Kitchen, B. J. 1977. Fractionation and characterization of membranes from bovine milk fat globule. J. Dairy Res. 44, 469-482. 

Mather, I. H., Weber, K. and Keenan, T. W. 1977. Membranes of mammary gland. XII. Loosely associated proteins and compositional heterogeneity of bovine milk fat globule membrane. J. Dairy Sci. 60, 394-402. 

Nielson, C. S. and Bjerrum, 0. J. 1977. Crossed immunoelectrophoresis of bovine milk fat globule membrane protein solubilized with non-ionic detergent. Biochim. Biophys. Acta 466, 496-509. 

Massart-Leen et al. (1981) analyzed bovine milk fat and goat milk fat for branched chain fatty acids. They did not find the same diversity of fatty acids in bovine as in goat milk fat and as previously reported. The authors suggested that the difference—the absence of branched chain acids other than iso and anteiso in bovine milk fat—could be caused by the relative inefficiency of the incorporations of methylmalonic acid into the biosynthetic pathway. 

Smith et al. (1978) have described a procedure for the GLC determination of cis and trans isomers of unsaturated fatty acids in butter after fractionation of the saturated, monoenoic, dienoic, and polyenoic fatty acid methyl esters by argentation TLC. Total trans acids were much higher, as measured by infrared spectrophotometry than by GLC, probably because some of the acids could have two or more of the trans bonds designated as isolated by infrared spectrophotometry. Enzymatic evaluation of methylene-interrupted cis, cis double bonds by lipoxidase resulted in lower values than those obtained by GLC. The authors mention that the lipoxidase method is difficult, requiring considerable skill, and suggest that their method is suitable for the determination of the principal fatty acids in complex food lipids such as bovine milk fat. 

Barbano, D. M. and Sherbon, J. W. 1975. Stereospecific analysis of high melting triglycerides of bovine milk fat and their biosynthetic origin. J. Dairy Sci. 58, 1-8. 

Breckenridge, W. C. and Kuksis, A. 1968. Specific distribution of short chain fatty acids in molecular distillates of bovine milk fat. J. Lipid Res. 9, 388-393. 

Hay, J. D, and Morrison, W. R. 1970. Isomeric monoenoic fatty acids in bovine milk fat. Biochim. Biophys. Acta 202, 237-243. 

Parodi, P. W. 1979. Stereospecific distribution of fatty acids in bovine milk fat trigylcer-ides. J. Dairy Res. 46, 75-81. 

In terms of composition, Table 7.5 shows that milk fat consists primarily of triglycerides with small amounts of di- and monoglycerides, phospholipids, sterols such as cholesterol, carotenoids, fat-soluble vitamins A, D, E, and K, and some traces of free fatty acids (Renner 1983 Christie 1983). The fatty acid composition of bovine milk fat is characterized by a high proportion of saturated fatty acids (60 to 70%), appreciable amounts of monounsaturated fatty acids (25 to 35%), and small amounts of polyunsaturated fatty acids (4%) (Lampert 1975). Milk fat... 

Briley, M. S. and Eisenthal, R. 1974. Association of xanthine oxidase with the bovine milk-fat-globule membrane. Catalytic properties of the free and membrane-bound enzyme. Biochem. J. 143, 149-157. 

Farrar, G. H. and Harrison, R. 1978. Isolation and structural characterization of alkali-labile oligosaccharides from bovine milk-fat-globule membrane. Biochem. J. 171, 549-557. 

Farrar, G. H., Harrison, R. and Mohanna, N. A. 1980. Comparison of lectin receptors on the surface of human and bovine milk fat globule membranes. Comp. Biochem. Physiol. 67B, 265-270. 

Greenwalt, D. E., Johnson, V. G. and Mather, I. H. 1985B. Specific antibodies to PAS-IV, a glycoprotein of bovine milk-fat-globule membrane, bind to a similar protein in cardiac endothelial cells and epithelial cells of lung bronchioles. Biochem J. 228, 233-240. 

Harrison, R., Higginbotham, J, D. and Newman, R. 1975. Sialoglycopeptides from bovine milk fat globule membrane. Biochim. Biophys. Acta 389, 449-463. 

Hayashi, S. and Smith, L. M. 1965. Membranous material of bovine milk fat globules. I. Comparison of membranous fractions released by deoxycholate and by churning. Biochemistry 4, 2550-2556. 

Huang, C. M., and Keenan, T. W. 1972A. Preparation and properties of 5 -nucleotidases from bovine milk fat globule membranes. Biochim. Biophys. Acta 274, 246-257. 

Kanno, C., Shimizu, M. and Yamauchi, K. 1977. Polydispersity and heterogeneity of the soluble glycoprotein isolated from bovine milk fat globule membrane. Agr. Biol. Chem. (Japan) 41, 83-87. 

Keenan, T. W., Freudenstein, C. and Franke, W. W. 1977A. Membranes of mammary gland. XIII. A lipoprotein complex derived from bovine milk fat globule membrane with some preparative characteristics resembling those of actin. Cytobiologie 14, 259-278. 

Mather, I. H., Tamplin, C. B. and Irving, M. G. 1980. Separation of the proteins of bovine milk-fat-globule membrane by electrofocusing with retention of enzymatic and immunological activity. Ear. J. Biochem. 110, 327-336. 

---