Fatty acids in animal fats

Chromosomes are composed of proteins and nucleic acids. 6. Fatty acids in vegetable oils are more unsaturated than fatty acids in animal fats. 

TABLE 19.1 J The Most Abundant Fatty Acids in Animal Fats, Vegetable Oils, and Biological Membranes ... 

Animal fats and vegetable oils mostly contain unsaturated straight chain fatty adds with 10 36 carbon atoms. The most common fatty acids are monoenoic and polyenoic fatty acids with 16-18 carbon atoms. The unsaturated fatty acids content of fats and oils ranges widely, from more than 90% of total fatty acids in rapeseed oil to less than 10% in coconut oil. Unsaturated fatty acids in animal fats occur in a much smaller concentration range, usually between 50 and 70% (Table 3.7). The only exception is fish oil, because it contains fatty acids with 20 22 carbon atoms and 4-6 double bonds (Table 3.12). The fat offreshwater fish differs in composition from the fatty adds in the fat of marine fish. Fish do not synthesise... 

Absorption and Deposition of CLA in Animal Tissues. Miller etal (27) described a method employing the methyl ester of conjugated dienes prepared from com oil as tracers of fat metabolism. It was postulated that the conjugated dienoic isomers could be differentiated from other fatty acids in body fat by spectrophotometric absorbance at 233 nm. 

Fats are esters of glycerol and fatty acids. Liquid fats are often called oils. Whether a fat is solid or liquid depends on the nature of the fatty acids. Solid animal fats contain mostly saturated fatty acids, while vegetable oils contain high amounts of unsaturated fatty acids. To avoid arteriosclerosis, hardening of the arteries, diets which are low in saturated fatty acids as well as in cholesterol are recommended. 

Such uniform fats do not occur to any extent in nature. Natural fats are statistical mixtures of glycerol triesters with three different fatty acids usually containing 12-20 carbon atoms and 0-4 cw-configured double bonds. A rule that seems often to be followed is that the few percent of unsaturated acids in animal fats are located on the central carbon atom of glycerol, whereas in plant fats their position is rather on Cl or C3. 

The methods used for determination of fat or oil in food are often based on extraction with either ethyl ether or petroleum ether and gravimetric determination of the extraction residue. These methods may provide unreliable or incorrect results, particularly with food of animal origin. As shown in Table 14.20, where a corned beef sample was analyzed, the amount and composition of fatty acids in the fat residue were influenced greatly by the analytical methods used. In addition to the accessible free lipids, the emulsifiers present and the changes induced by autoxidation affect the amount of extractable lipids and the lipid-to-nonlipid ratio in the residue. The use of a standard method still does not eliminate the disadvantages shown by analytical methods of fat analysis. Therefore, in questionable cases, quantitative determination of fatty acids and/or glycerol is recommended. 

Percent (m/m) saturated and unsaturated fatty acids in selected fats and oils H Polyunsaturated H Monounsaturated Saturated FIGURE 18.7 Vegetable oils have lowt melting points because they have a higher percentage of unsaturated fatty acids than do animal fats. 

The fats of the diet serve as a source of the essential fatty acids—arachidonic, linoleic, and linolenic acid, but only linoleic acid is required preformed in the diet. Although meats provide fat, the vegetable oils are generally richer sources of the essential fatty acids than animals fat hence, no deficiency of fatty acids is likely to develop in a meatless diet unless there is impaired lipid absorption. 

Palmitoleic acid is commonly found at low levels in animal and plant tissues (Gunstone, 1994). It is present in most fish oils at levels of around 10% (w/w) of total fatty acids. In animal depot fat, the level of palmitoleic acid varies between 3% and 10%, depending on location and animal species. In human and animal milk, the proportion of palmitoleic acid, together with other 16 1 isomers, is typically 2-6%, with exceptionally high levels found in grey seal milk (16%) and camel colostrum (14%) and milk (10%) (Gorban and Izzeldin, 2001). 

CH3-[CHi]5.CH CH-[CH2]g-C02H. A white solid, m.p. 43-44°C, which is present in small quantities in animal fats and in milk. It is the only naturally occurring fatty acid with the trans configuration. 

The saturated fatty acids, stearic [57-11-4] and palmitic [57-10-3], are found in animal fats and dairy products. Extensive studies point to the deleterious effect of these acids on arterial walls as a result it is recommended that saturated fatty acid intake be carefully controlled and intake limited (23). 

Sterols. Sterols (4) are tetracycHc compounds derived biologically from terpenes. They are fat-soluble and therefore are found in small quantities in fats and oils. Cholesterol [57-88-5] (4a) is a common constituent in animal fats such as lard, tallow, and butterfat. The hydroxyl group can be free or esterified with a fatty acid. 

Historically, many attempts have been made to systematize the arrangement of fatty acids in the glyceride molecule. The even (34), random (35), restricted random (36), and 1,3-random (37) hypotheses were developed to explain the methods nature utilized to arrange fatty acids in fats. Invariably, exceptions to these theories were encountered. Plants and animals were found to biosynthesize fats and oils very differently. This realization has led to closer examination of biosynthetic pathways, such as chain elongation and desaturation, in individual genera and species. 

Triacylglycerol (Section 27.1) A lipid, such as those found in animal fat and vegetable oil. that is, a triester of glycerol with long-chain fatty acids. 

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