Fatty acids compositions

Fatty acid determination in oils is extremely important, enabling lipid scientists to classify an oil correctly, both botanically and in accordance with commercial gradings. The two most common reactions for preparing the methyl esters of fatty acids, both free and esterified as triglycerides, are  

direct trans-esterification in anhydrous methanol in the presence of an acidic catalyst (sulphuric acid, hydrogen chloride, boron trifluoride) or basic catalyst (potassium hydroxide, sodium methoxide). 

esterification proceeding through a first step in which the oil sample is heated in methanol-sodium methylate, followed by a second step in which the reaction mixture of step one is heated in the presence of concentrated sulphuric acid to give the methyl esters of the originally free fatty acids, together with the methyl esters of acids of glycerides. 

The procedure of method 1. is quicker than method 2. and will give a complete picture of the fatty acid composition of an oil only when no free acids are present in the sample method 2. needs to proceed through two steps but produces the most complete picture of both the free and esterified fatty acids comprising an olive oil. 

The methyl esters obtained are readily analysed qualitatively and quantitatively by gas chromatography, and the data obtained allow detection of sophistication. In the literature there is a wealth of fatty acid analysis data on virgin olive oils, all constantly reporting almost the same qualitative composition. However, what is surprising is the systematic attitude of so many researchers not reporting the presence of vaccenic acid, 11 -ds-octadecenoic acid, an isomer of oleic acid. The presence of this positional isomer of oleic acids was first described in olive oil by Tulloch and Craig (1964). 

The fatty acid composition of milk fat is not stable and is influenced by a number of factors. These include, breed of cow, stage of lactation and type, and quality and quantity of feed (Grummer, 1991 Beaulieu and Palmquist, 1995 Hawke and Taylor, 1995 Auldist et al., 1998 Zegarska et al., 2001). These issues are discussed in detail in Chapter 2 (Palmquist). 

Fatty Acid January March May-June July-August Oct-Nov 

Similar seasonal trends in fatty acid composition have been found in other countries where the pattern of dairy husbandry practices is similar (Hughebaert and Hendrickx, 1971 Muuse et al., 1986 Lindmark-Mansson et al., 2003). 

Bovine milk fat contains various triacylglycerols, which vary considerably in molecular weight and degree of unsaturation. This complexity is the direct result of the large number and wide variety of fatty acids which make up the triacylglycerols. 

As noted earlier, there are some 400 fatty acids in milk fat, which means that theoretically milk fat could contain many thousand triacylglycerols. Even if one considers only the 15 or so fatty acids that are present at concentrations above 1% (Table 1.2), and ignores the placement of these fatty acids at specific positions on the triacylglycerol molecule, there are still 680 compositionally different triacylglycerols. 

Typical fatty acid composition of commodity soybean oil, in comparison with the other major vegetable oils, is shown in Table 2.3. Soybean oil has a high content of linoleic acid, and a lower level of linolenic acid. These are both essential fatty acids for humans and therefore of dietary importance, but they are also the cause of oxidative instability of this oil. Processing techniques, such as hydrogenation and lipid modification through traditional plant breeding or genetic transformation, have been used to modify the fatty acid composition to improve its oxidative or functional properties. 

Triacylglycerols (TAG) are the primary neutral lipids in soybean oil. Due to the high concentration of unsaturated fatty acid in soybean oil, nearly all the TAG molecules contain at least two unsaturated fatty acids, and di- and trisaturates are essentially absent (List el al. 1977). In natural oils and fats, the fatty acids are not usually randomly distributed among the three hydroxyl groups of glycerol but are associated in particular patterns. Several theories of regiospecific distribution exist (Litchfield 1972), but the 1,3-random, 2-random theory is most widely accepted. The stereospecific distribution of fatty acyl groups in soybean oils 

Fatty acid Soybean Canola Cottonseed Sunflower Peanut 

---

Com oil s flavor, color, stabiHty, retained clarity at refrigerator temperatures, polyunsaturated fatty acid composition, and vitamin E content make it a premium vegetable oil. The major uses are frying or salad appHcations (50%) and margarine formulations (35%). 

There are physical—chemical differences between fats of the same fatty acid composition, depending on the placement of the fatty acids. For example, cocoa butter and mutton tallow share the same fatty acid composition, but fatty acid placement on the glycerin backbone yields products of very different physical properties. 

Table 2. Fatty Acid Compositions of Naturally Occurring Fats and Oils ...

Measurement of Unsaturation. The presence of double bonds in a fatty acid side chain can be detected chemically or through use of instmmentation. Iodine value (IV) (74) is a measure of extent of the reaction of iodine with double bonds the higher the IV, the more unsaturated the oil. IV may also be calculated from fatty acid composition. The cis—trans configuration of double bonds may be deterrnined by infrared (59) or nmr spectroscopy. Naturally occurring oils have methylene-intermpted double bonds that do not absorb in the uv however, conjugated dienes maybe deterrnined in an appropriate solvent at 233 nm. 

Table 3. Fatty Acid Composition of Oil-Free Lecithins, ...

To determine the phosphoHpid and fatty acid compositions chromatographic methods (28) like gas chromatography (gc), thin-layer chromatography (tic), and high performance Hquid chromatography (hlpc) are used. Newer methods for quantitative deterrnination of different phosphoHpid classes include P-nmr (29). 

Table 4. Fatty Acid Compositions, Wt %, of Fats and Oils Commonly Used in Alkyd Resins...

Lipids. Representative fatty acid compositions of the unprocessed triglyceride oils found in the four oilseeds are given in Table 4 (see Fats and FATTY oils). Cottonseed, peanut, and sundower oils are classified as oleic—linoleic acid oils because of the high (>50%) content of these fatty acids. Although the oleic and linoleic acid content of soybean oils is high, it is distinguished from the others by a content of 4—10% of linolenic acid, and hence is called a linolenic acid oil. 

Table 1. Typical Fatty Acid Composition of Tall Oil Products...

Oils are mixtures of mixed esters with different fatty acids distributed among the ester molecules. Generally, identification of specific esters is not attempted instead the oils are characterized by analysis of the fatty acid composition (8,9). The principal methods have been gas—Hquid and high performance Hquid chromatographic separation of the methyl esters of the fatty acids obtained by transesterification of the oils. Mass spectrometry and nmr are used to identify the individual esters. It has been reported that the free fatty acids obtained by hydrolysis can be separated with equal accuracy by high performance Hquid chromatography (10). A review of the identification and deterrnination of the various mixed triglycerides is available (11). 

Membranes are composed of phospholipids and proteins. The fatty acid composition of the phospholipids in a membrane influences how it is affected by the cold. In general, as the temperature of a cell is lowered the lipids in the membrane bilayer undergo a phase transition from a liquid crystalline (fluid) state to a gel (more solid) state. The temperature at which this transition takes place is very narrow for phospholipids composed of a simple mixture of fatty acids, but is quite broad for the phospholipids in cellular membranes. It is usually implied from various methods... 

Peroxidation of lipids is another factor which must be considered in the safety evaluation of liposome administration. Smith and coworkers (1983) demonstrated that lipid peroxides can play an important role in liver toxicity. Allen et al. (1984) showed that liposomes protected by an antioxidant caused less MPS impairment than liposomes subjected to mild oxidizing conditions. From the study of Kunimoto et al. (1981) it can be concluded that the level of peroxidation in freshly prepared liposome preparations and those on storage strongly depends both on the phospholipid fatty acid composition and on the head group of the phospholipid. Addition of appropriate antioxidants to liposomes composed of lipids which are liable to peroxidation and designed for use in human studies is therefore necessary. 

The amounts and fatty acid compositions of the various phospholipids vary among the different cellular membranes. 

The fatty acid composition of the Baker cypress is comparatively complex. The major saturated acids were identified as palmitic (16 0) [chain lengthmumber of double bonds], stearic (18 0), and arachidic (20 0) with only minor contributions from... 

Exposures of 10 weeks (5 days/week) to 2,500 mg/kg/day trichloroethylene in com oil by gavage resulted in altered myelin thickness in the rat mental nerve, a branch of the trigeminal nerve (Barret et al. 1991). Effects of similar exposures on the rat trigeminal nerve included decreased fiber diameter and altered fatty acid composition in total lipid extracts, indicative of demyelination (Barret et al. 1992). Stronger effects were seen with the trichloroethylene decomposition product dichloroacetylene. 

Okamoto T, Shiwaku K. 1994. Fatty acid composition in liver, serum, and brain of rat inhalated with trichloroethylene. Exp Toxicol Pathol 46 133-141. 

MARCKMANN p, sandstrOm b, jespersen J (1990) Effect of total fat content and fatty acid composition in diet on factor Vll coagulant activity and blood lipids, Atherosclerosis, 80, 227-33. 

Tsitko IV, GM Zaitsev, AG Lobanok, MS SaUdnoja-Salonen (1999) Effect of aromatic compounds on cellular fatty acid composition of Rhodococcus opacus. Appl Environ Microbiol 65 853-855. 

Ethanol and choline glycerolipids were isolated from calf brain and beef heart lipids by PTLC using silica gel H plates. Pure ethanol amine and choline plasmalogens were obtained with a yield of 80% [74]. Four phosphohpid components in the purple membrane (Bacteriorhodopsin) of Halobacterium halobium were isolated and identified by PTLC. Separated phosphohpids were add-hydrolyzed and further analyzed by GC. Silica gel G pates were used to fractionate alkylglycerol according to the number of carbon atoms in the aliphatic moiety [24]. Sterol esters, wax esters, free sterols, and polar lipids in dogskin hpids were separated by PTLC. The fatty acid composition of each group was determined by GC. 

---