Origins of the Fatty Acids

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 de novo synthesis of fatty acids in the mammary gland utilizes mainly acetate and some (3-hydroxybutyrate. These precursors arise from the microbial fermentation of cellulose and related materials in the rumen. Once in the mammary gland, acetate is activated to acetyl-CoA. The mechanism of fatty acid synthesis essentially involves the carboxylation of acetyl-CoA to malonyl-CoA, which is then used in a step-wise chain elongation process. This leads to a series of short-chain and medium-chain length fatty acids, which differ by two CH2 groups (e.g., 4 0, 6 0, 8 0, etc.) (Hawke and Taylor, 1995). These are straight-chain, even-numbered carbon fatty acids. However, if a precursor such as propionate, valerate or isobutyrate, rather than acetate, is used, branched-chain or odd-numbered carbon fatty acids are synthesised (Jenkins, 1993 see Chapter 2). 

The net result of these processes is that the fatty acids in the mammary gland, which originate from the dietary lipids, consist of substantial quantities of 16 0, 18 0 and oleic acid, small amounts of linoleic and linolenic acids, and limited quantities of other monoenoic and dienoic fatty acids such as llt-18 l and 9c, llt-18 2. 

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Starting from the carboxylic carbon (A-designation 12-hydroxy-oleic acid or ricinoleic acid). It is used to characterize the origin of the fatty acids in nutrition circle. 

The exact local origin of the fatty acid component of the glycosphingolipids in the central nervous system is not known for certain. Palmitate and oleate can pass from the blood into the brain or may be synthesized in the cytoplasm of the brain cells. To produce the longer fatty acid chains, the fatty acid elongation system of the mitochondria, e.g., those of oligodendrocytes, may then convert palmitate to C18 to Gae fatty acids (Fig. 2). 

Analytical results are often represented in a data table, e.g., a table of the fatty acid compositions of a set of olive oils. Such a table is called a two-way multivariate data table. Because some olive oils may originate from the same region and others from a different one, the complete table has to be studied as a whole instead as a collection of individual samples, i.e., the results of each sample are interpreted in the context of the results obtained for the other samples. For example, one may ask for natural groupings of the samples in clusters with a common property, namely a similar fatty acid composition. This is the objective of cluster analysis (Chapter 30), which is one of the techniques of unsupervised pattern recognition. The results of the clustering do not depend on the way the results have been arranged in the table, i.e., the order of the objects (rows) or the order of the fatty acids (columns). In fact, the order of the variables or objects has no particular meaning. 

The repertoire of chemicals that can be used for communication is limited by the biosynthetic ability of the insect. Compared to other insect orders, pheromone biosynthesis in Hymenoptera has received little study [191]. However, the biosynthetic origins of chemically diverse hymenopteran semiochemicals likely include aromatic, fatty acid, and terpenoid pathways as well as simple modifications of host-derived precursors. Notable recent studies include the biosynthesis of the fatty acid components (2 )-9-oxodec-2-enoic acid 52 and (2 )-9-hydroxydec-2-enoic acid of the honeybee queen mandibular pheromone from octadecanoic acid [192,193], and the aliphatic alcohol and ester... 

The fourth and last step of the /3-oxidation cycle is catalyzed by acyl-CoA acetyltransferase, more commonly called thiolase, which promotes reaction of /3-ketoacyl-CoA with a molecule of free coenzyme A to split off the carboxyl-terminal two-carbon fragment of the original fatty acid as acetyl-CoA The other product is the coenzyme A thioester of the fatty acid, now shortened by two carbon atoms (Fig. 17-8a). This reaction is called thiolysis, by analogy with the process of hydrolysis, because the /3-ketoacyl-CoA is cleaved by reaction with the thiol group of coenzyme A... 

Although LOX activity is important to the plant s defense against pathogens, there are negative aspects of the enzyme in foods. LOX activity and the resulting fatty acid hydroperoxide products initiate free radical chains that modify proteins (particularly residues of Trp, His, Cys, Tyr, Met, and Lys) as well as vitamins or their precursors (e.g., carotene and tocopherol). Evidence of such free radical reactions is often visibly observed as loss of carotenoid/chlorophyll pigments in improperly blanched frozen foods. Another consequence of these free radical reactions is the development of potent off-flavors, many of which originate from decomposition of the fatty acid hydroperoxide products. 

The original DEBS 1-TE cell-free system allowed several other features of polyketide chain extension to be examined by using well-known inhibitors of specific enzyme activities. Incubation of DEBS 1 -TE with the serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF) resulted in a significant decrease in biosynthetic activity. This result emphasized the mechanistic similarity between the targeted TE domain and the serine protease enzymes. Addition of the fatty acid inhibitor cerulenin [38] also reduced production of the lactone, consistent with the evolutionary kinship between these two classes of enzymes. Inhibition of DEBS 1+TE by cerulenin was also reported [33],... 

Matter, L. (1992) Determination of the animal of origin of dairy products and raw and cooked meats by GC analysis of the fatty acid methyl esters (FAME) obtained by transesterification. J. High Res. 

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