Component Fatty Acids

Even-numbered straight-chain saturated and unsaturated fatty acids make up the largest proportion of fatty acids in fats and oils. Minor amounts of odd-carbon-number acids, branched-chain acids, and hydroxy acids may also be present. Processed fats, especially hydrogenated fats, may contain a variety of geometric and positional isomers. The division of fatty acids into saturated and unsaturated groups is important because it generally reflects on the melting properties of the fat of which they are a part. There are some exceptions to this rule. Short-chain saturated fatty acids such as those present in milk fats and lauric fats have

Cerebrosides

Phosphatidyl esters

Plasmalogens

Sphingomyelin

Hexoses

Sphingosine

Sphingosine

Glyceryl ether

Phosphoric acid amino alcohols

Fatty aldehydes

Glyceryl ether

Figure 1. Interrelationship of the lipids. 721

very low melting points; unsaturated trans isomers have much higher melting points than the cis isomers and are therefore comparable to saturated fatty acids in their effect on melting characteristics.

Some of the important saturated fatty acids are listed in Table 1 with their systematic and common names. The unsaturated fatty acids are listed in Table 2. The naturally occurring unsaturated fatty acids are almost exclusively in the cis form. Trans acids are abundant in ruminant milk fats and in hydrogenated fats.

The depot fats of higher land animals consist mainly of palmitic, oleic, and stearic acids and are high in saturation. The fats of birds are somewhat more complex. The fatty acid compositions of the major food fats of this group are listed in Table 3. The kind of feed consumed by the animals greatly influences the fatty acid composition of the depot fats. For example, the high linolenic acid content of the horse fat in Table 3 is the result of pasture feeding. Animal depot fats are generally low in polyunsaturated fatty acids. The iodine value of beef fat is about 50 and of lard about 60.

Ruminant milk fat has an extremely complex fatty acid composition. The following fatty acids are present in cow's milk fat (3): even and odd saturated acids from 2:0 to 28:0; even and odd monoenoic acids from 10:1 to 26:1 with the exception of 11:1, and-including positional and geometric isomers; even unsaturated fatty acids from 14:2 to 26:2 with some conjugated trans isomers; monobranched fatty acids 9:0 and 11:0 to 25:0; some iso and some anteiso (iso acids have a methyl branch on the penultimate carbon, anteiso on the next to penultimate carbon; multibranched acids from 16:0 to 28:0, both odd and even with three to five methyl branches; and, finally, a number of keto, hydroxy, and cyclic acids.

Marine oils also contain a large number of different fatty acids. As many as 50 to 60 fatty acids have been reported (4). The 14 major ones consist of few saturated fatty acids (14:0, 16:0, and 18:0) and a larger number of unsaturated fatty acids with 16 to 22 carbon atoms and up to 6 double bonds. This provides the possibility for many positional isomers. It is customary to number carbon atoms of

Table 1. Saturated Even- and Odd-Carbon-Numbered Fatty Acids

Systematic name

Common name

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