Fatty acids in triglycerides

X 11 X 20) mm. (a) Cross-section of the human lower leg of a volunteer. Two volume elements in musculature and one voxel inside the tibial bone marrow are indicated, (b) Spectrum recorded from the tibialis anterior (TA) muscle shows low lipid content of approximately 1% volume fraction, (c) Spectrum from the soleus (SOL) muscle indicates higher lipid content than in TA. (d) Spectrum from yellow bone marrow with dominating signal from fatty acids in triglycerides. 

A remarkable feature of lipids, either vegetal or animal, is that they share the same fatty acids in triglycerides in the range C12-C20 (Table 14.3). However, there are significant differences in composition. Thus, soybean, sunflower and rapeseed oils are all based on C18 acids, the first two being richer in unsaturated linoleic acid, which could introduce a problem of stability with respect to oxidation. The palm oil has an important amount of C16 acid. Coconut oil is given as an example of Cl2-04 rich oil. As in palm oil the composition of tallow spreads over Cl6-08 acids. 

Christie, W.W. (1986) The positional distribution of fatty acids in triglycerides. Analysis of Oils and Fats (eds. R.J. Hamilton and J.B. Rossell), Elsevier Applied Science, Essex, pp. 313-339. 

Parodi, P.W. 1982. Positional distribution of fatty acids in triglycerides from milk of several species of mammals. Lipids. 17, 437-442. 

Mason and co-workers [39,40] developed a method for the transesterification of fatty acids in triglycerides in the presence of 2,2-dimethoxypropane. To 35 qmol of the triglyceride in a 25 ml erlenmeyer flask 10 ml of benzene, 4 ml of dimethoxypropane, 5 ml of methanol and 1 ml of 2 N sodium methanolate are added. After mixing, the mixture is allowed to stand for 5 min and an amount of methanolic HC1 is then added such that about a 0.3 mmol excess remains. The mixture is again stirred, allowed to stand for 50 min, about 1.5 g of a solid neutralizing agent is added and it is stirred for 30 min. The precipitate is allowed to sediment, the supernatant is decanted into a 25-ml volumetric flask and the volume is made up with methanol, with which the precipitate was washed. Aliquots are injected into the chromatograph. 

A stereospecific numbering system (Sn) is used to indicate the location of specific fatty acids in triglyceride molecules such as in 1-stearoyl-2-oleoyl-3-myristoyl-Sn-glycerol the respective fatty acids are indicated in the 1, 2, and 3 positions. This kind of information is very valuable in relating properties of certain fats to compositional data. Table 4.4... 

Oleic acid is the most abundant fatty acid in triglycerides in humans and most mammals. Flence it is found in abundance in beef fat (tallow), pork fat (lard), and butter (see the table) but it is also present in abundance in almond oil, peanut oil, and palm oil (see the table). This high content with a lower proportion of saturated fatty acids makes these fats have a low melting temperature hence they are liquid (oils) at room temperature. On the other hand, the animal fats tend to be solid as a result of also having a high content of saturated fatty acids. 

Table 3.144 Positional distribution of fatty acids in triglycerides of seed oils (Brockerhoff and Hoyle, 1963 Brockerhoff and Yurkowski, 1966 Brockerhoff a/., 1966) ...

The three carbonyl spectra of egg lipids illustrated in Figs 4.20(a)-(c) demonstrate the pathway of co-3 fatty acids in triglycerides and phospholipids. The eggs are enriched with co-3 fatty acids by a special hen feed. Nearly all co-3 fatty acids are found in the phospholipids, the highest amounts in phosphatidylethanolamine (PE) (Diehl et aL, 1996a). 

As Table 5.8 shows, different fatty acids have different melt points. Although fatty acids in triglyceride form behave differently from their free fatty acid state, still the above table helps in understanding the melt characteristics of the triglyceride as a whole, especially when comparing two oils. 

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