Fatty acids in milk

Stonyfield farms, a commercial processor in the United States, has initiated a "Greener Cow Project" to decrease CIT4 emissions by feeding cows a diet rich in natural omega-3 sources http / www.stonyfield.com/ search/index.jsp q=greener-icow x=12 y=8. Preliminary results indicate a reduction of enteric emissions by an average of 12% and an increase in omega-3 fatty acids in milk. 

Saturated fatty acids (no double bonds), such as myristic, palmitic, and stearic, make up two-thirds of milk fatty acids. Oleic acid is the most abundant unsaturated fatty acid in milk, with one double bond. Triglycerides account for 98% of milk fat. The small amounts of mono-, diglycerides, and free fatty acids in fresh milk may be... 

Both maternal and infant factors determine the final amount of drug present in the nursing child s body at any particular time. Variations in the daily amount of milk formed within the breast (e.g., changes in blood flow to the breast) as well as alterations in breast mUk pH wUl affect the total amount of drug found in mUk. In addition, composition of the milk will be affected by the maternal diet for example, a high-carbohydrate diet will increase the content of saturated fatty acids in milk. 

Milk fats, especially ruminant fats, contain a very wide range of fatty acids more than 400 and 184 distinct adds have been detected in bovine and human milk fats, respectively (Christie, 1995). However, the vast majority of these occur at only trace concentrations. The concentrations of the principal fatty acids in milk fats from a range of species are shown in Table 3.6. Notable features of the fatty acid profiles of milk lipids include ... 

The usual diet of ruminants consists of fresh and preserved herbage and cereals. As a result of microbial activity in the rumen, esterified dietary fatty acids are hydrolyzed, short chain fatty acids are produced by fermentation of cellulose and other polysaccharides, unsaturated fatty acids are hydrogenated and/or converted to geometric (trans) and positional isomers, and microbial lipids are synthesized. These activities account in part for the enormous diversity of fatty acids in milk and the unique features short-chain and a high proportion of long chain saturated fatty acids. (Patton and Jensen, 1976 Christie, 1979B). 

Table 4.3. Composition and Stereospecific Distribution of Fatty Acids in Milk Fat Trigylcerides from Bimonthly Samples of Maleny Butter.

Parodi, P. W. 1976. Distribution of isomeric octadecenoic fatty acids in milk fat. J. Dairy Sci. 59, 1870-1873. 

Harper, W. J., Schwartz, D. P. and El-Hagarawy, I. S. 1956B. A rapid silica gel method for measuring total free fatty Acids in milk. J. Dairy Sci. 39, 46-50. 

Kuzdzal-Savoie, S. 1980. Flavour impairment of milk and milk products due to lipolysis. VII. Determination of free fatty acids in milk and milk products. Int. Dairy Fed. Bull. 118, pp. 53-66. 

Salih, A. M. A. and Anderson, M. and Tuckley, B. 1977. The determination of short and long chain free fatty acids in milk. J. Dairy Res. 44, 601. 

Shipe, W. F., Senyk, G. F. and Fountain, K. B. 1980B. Modified copper soap solvent extraction method for measuring free fatty acids in milk. J. Dairy Sci. 63, 193-198. 

Worstorff, H. 1975. Mechanical factors in the milking plant affecting the level of free fatty acids in milk. Ind. Dairy Fed. 86, 156-161. 

It is important to bear in mind when discussing the effect of dairy fat in association to heart disease that dairy products contain many different saturated fatty acids that do not exert the same biological response in terms of, for example, cholesterol levels. The saturated fatty acids in milk fat include shorter and medium chain fatty acids (2 0-10 0), lauric acid (12 0), myristic acid (14 0), palmitic acid (16 0), and stearic acid (18 0). Other fatty acids in milk fat are oleic acid (18 1) and linoleic acid (18 2n-6) as indicated in Table 1.2. 

TABLE 1.2 Percentages of the different fatty acids in milk fat... 

IDF (1991). Determination of Free Fatty Acids in Milk and Milk Products (Standard 265). International Dairy Federation, Brussels. 

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... 

The fatty acids of bovine milk fat arise from two sources synthesis de novo in the mammary glands and the plasma lipids originating from the feed. The fatty acids from these two sources differ in their structure. The fatty acids that are synthesised de novo are short-chain and medium-chain length acids, from 4 0 to 14 0 and also some 16 0, while the Cis fatty acids and some 16 0 arise from the plasma lipids. De novo fatty acid synthesis accounts for approximately 45% (w/w) of the total fatty acids in milk fat, while lipids of dietary origin account for the rest (Moore and Christie, 1979). 

The presence of Qg tram-fatty acids in milk fat is the result of incomplete biohydrogenation of the unsaturated dietary lipids in the rumen. These fatty acids have attracted attention because of their adverse nutritional affects. Clinical trials have shown that traus-octadecenoic acids, relative to the cis isomer, can increase the LDL-cholesterol and decrease the HDL-cholesterol, thus, producing an unfavourable affect on the LDL HDL ratio (Mensink and Katan, 1993). 

The quantitative determination of individual isomers of tram-18 1 fatty acids in milk fat is not straightforward. It involves a multi-stage analytical procedure (i.e., transesterification of milk fat, argentation TLC of the fatty acid esters to separate the civ-isomers and tram-isomers, followed by capillary GC). This method gives an almost complete separation of the 13 individual tram-18 1 isomers, from A4 to A16 (Precht and Molkentin, 1996). 

There are about 200 minor monoenoic, dienoic and polyenoic fatty acids in milk fat ranging in chain length from C10 to C24, and consisting of both positional and cisltrans isomers. A number have considerable nutritional significance for example, eicosapentaenoic acid (20 5,0.09%) and docosahex-aenoic acid (22 6,0.01%) are present in the metabolic pathway of the n-3 fatty acids, while arachidonic acid (20 4, 0.14%) is part of the n-6 pathway. 

As noted earlier, there are some 400 fatty acids in milk fat, which means that theoretically milk fat could contain many thousand triacylglycerols. Even if one considers only the 15 or so fatty acids that are present at concentrations above 1% (Table 1.2), and ignores the placement of these fatty acids at specific positions on the triacylglycerol molecule, there are still 680 compositionally different triacylglycerols. 

The fatty acids in milk fat are derived from two sources, de novo synthesis of fatty acids in the mammary gland and plasma lipids (see Pal-quist, Chapter 2). De novo synthesis generally involves short-chain and medium-chain fatty acids and some 16 0. The proportions of various fatty acids depend on the specific balance between enzymatic chain elongation and chain termination. The plasma lipids are derived from the diet and also from storage in the body tissues. For non-ruminants, the diet has a large influence on the fatty acid composition but for ruminants, biohydrogenation in the rumen results in much less impact of diet on the final fatty acids absorbed into the bloodstream. 

Table 1.17. Major fatty acids in milk triacylglycerols from various species...

Hebeisen, D.F., Hoeflin, F., Reusch, H.P., Junker, E., Lauterburg, B.H. 1993. Increased concentrations of omega-3 fatty acids in milk and platelet rich plasma of grass-fed cows. Int. J. Vitam. Nutr. Res., 63, 229-233. 

Jensen, R.G. 2000. Fatty acids in milk and dairy products. In, Fatty Acids in Foods and their Health Implications. 2nd edn (C.K. Chow, ed.), pp. 109-123, Marcel Dekker Inc., New York, NY. 

Palmquist and Conrad (1971) fed or intravenously infused 1-14C palmitic acid into lactating cows and mathematically calculated the partition of 14C secreted into milk fat as originating from two pools, diluted due to turnover of the dietary and endogenous fatty acids. The proportions of the long-chain fatty acids in milk derived from the diet were influenced by the... 

More than 95% of Ci8 and longer-chain fatty acids in milk fat are derived from the blood TAG-rich lipoproteins. Non-esterified fatty acids are... 

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