Fatty acid profile of milk lipids

Milk fats, especially ruminant fats, contain a very wide range of fatty acids more than 400 and 184 distinct acids 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  

Ruminant milk fats contain a high level of butanoic acid (C4.0) and other short-chain fatty acids. The method of expressing the results in Table 3.6 (%, w/w) under-represents the proportion of short-chain acids-if expressed as mol %, butanoic acid represents c. 10% of all fatty acids (up to 15% in some samples), i.e. there could be a butyrate residue in c. 30% of all triglyceride molecules. The high concentration of butyric (butanoic) acid in ruminant milk fats arises from the direct incorporation of )S-hydroxybutyrate (which is produced by micro-organisms in the rumen from carbohydrate and transported via the blood to the mammary gland where it is reduced to butanoic acid). Non-ruminant milk fats contain no butanoic or other short-chain acids the low concentrations of butyrate in milk fats of some monkeys and the brown bear require confirmation. 

The concentration of butanoic acid in milk fat is the principle of the widely used criterion for the detection and quantitation of adulteration of butter with other fats, i.e. Reichert Meissl and Polenski numbers, which are measures of the volatile water-soluble and volatile water-insoluble fatty acids, respectively. 

Short-chain fatty acids have strong, characteristic flavours and aromas. When these acids are released by the action of lipases in milk or 

The milk fats from marine mammals contain high levels of long-chain, highly unsaturated fatty acids, presumably reflecting the requirement that the lipids of these species remain liquid at the low temperatures of their environments. 

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The fatty acid profile of ruminant fats (milk and adipose tissue) is relatively constant due to the buffering action of the rumen microflora that modify ingested lipids. However, the proportions of various fatty acids in milk lipids show seasonal/nutritional/lactational variations (Figure 3.5) which are reflected in seasonal variations in the hardness of milk fat (Figure 3.7). 

The fatty acid profile can be modified substantially by feeding encapsulated (protected) polyunsaturated oils to cows. The oil is encapsulated in a film of polymerized protein or in crushed oil-rich seeds. The encapsulating protein is digested in the abomasum, resulting in the release of the unsaturated lipid, a high proportion of the fatty acids of which are then incorporated into the milk (and adipose tissue) lipids. The technical... 

Aurousseau et al. 2004 for a review see Scollan et al. 2006) or the effects of lipid-enriched diets (Mele et al. 2007 W sowska et al. 2006 Nod et al. 2007) on ruminal BH and consequently on meat and milk fatty acid profile. However, this extensive topic is out of the scope of the present chapter and will not be further treated. 

To obtain a total fatty acid profile, to include co3 fatty acids, and other potentially beneficial fatty acids such as GLA, the approach is normally straightforward and involves extraction of lipids in the presence of an appropriate, derivatization of fatty acids to methyl esters, and analysis by GC. Appropriate extraction methods, depending on the type of food and lipids presents, must be employed to extract the total lipids efficiently. An alternative is to hydrolyze the sample directly to release all the fatty acids in the free form followed by derivatisation. An appropriate methylation step is required. Alkaline methods are milder, but will only derivatize EFA. Acidic methods are used to derivatize samples containing FFA with or without EFA. Separation of FAME can normally be achieved on Carbowax type columns of medium length, but samples such as milk fats or PHVO, containing complex mixtures of trans fatty acids, require longer polar columns and may require the use of additional techniques. Milk fats also contain SCFA and specific precautions or adaptations of protocols are necessary for their analysis. 

Factors affecting the fatty acid profile and CLA level of cow s milk include breed, diet, and stage of lactation (early-lactation milk generally has a lower solid fat content, i.e. a lower proportion of saturated fat). Even among animals with similar characteristics, CLA levels can differ considerably, probably due to differences in rumen microbial populations or levels of A -desaturase activity. Unsaturated lipids can be partially protected from rumen hydrogenation by feeding whole seeds, encapsulated fatty acids, or fatty acids as their calcium salts. 

Milk fat contains a number of different lipids, but is predominately made up of triacylglycerols (TAG) (98%). The remaining lipids are diacylglycerols (DAG), monoacylglycerols (MAG), phospholipids, free fatty acids (FFA) and sterols. Milk fat contains over 250 different fatty acids, but 15 of these make up approximately 95% of the total (Banks, 1991) the most important are shown in Table 19.1. The unique aspect of bovine, ovine and caprine milk fat, in comparison to vegetable oils, is the presence of high levels of short-chain volatile FFAs (SCFFA), which have a major impact on the flavor/aroma of dairy products. Most cheeses are produced from either bovine, ovine or caprine milk and the differences of their FFA profile are responsible for the characteristic flavor of cheeses produced from such milks (Ha and Lindsay, 1991). 

All microalgae contain sterols (typically up to 10% of total lipid) either as the free sterol (most common) or as a fatty acid ester, glycoside or sulphate (Ghosh et /., 1998 Volkman et al, 1998 Milke et al, 2008). Sterol profiles can be characteristic of a particular class, family, genus or even species and so are often applied to chemotaxonomic and phylogenetic studies. Profiles... 

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