III. CHEMICAL COMPOSITION OF FATS

The main components of edible fats and oils are triglycerides. The minor components include mono- and diglycerides, free fatty acids, phosphatides, sterols, fat-soluble vitamins, tocopherols, pigments, waxes, and fatty alcohols. The free fatty acid content of crude oil varies widely based on the source. Other than the free fatty acids, crude vegetable oils contain approximately two percent of these minor components. Animal fats contain smaller amounts.

A. The Major Component - Triglycerides

A triglyceride consists of three fatty acids attached to one glycerol molecule. If all three fatty acids are identical, it is a simple triglyceride. The more common forms, however, are the "mixed" triglycerides in which two or three kinds of fatty acids are present in the molecule. Illustrations of typical simple and mixed triglyceride molecular structures are shown below.

Figure 1

Diagrams of simple and mixed triglycerides


The fatty acids in a triglyceride define the properties and characteristics of the molecule and are discussed in greater detail in Chapter IV.

B. The Minor Components

1. Mono- and Diglycerides. Mono- and diglycerides are mono- and diesters of fatty acids and glycerol. They are used frequently in foods as emulsifiers. They are prepared commercially by the reaction of glycerol and triglycerides or by the esterification of glycerol and fatty acids. Mono- and diglycerides are formed in the intestinal tract as a result of the normal digestion of triglycerides. They occur naturally in very minor amounts in both animal fats and vegetable oils. Oil composed mainly of diglycerides has also been used as a replacement for oil composed of triglycerides. Illustrations of mono- and diglyceride molecular structures are provided below:

Figure 2

Diagrams of mono- and diglycerides.

2. Free Fatty Acids. As the name suggests, free fatty acids are the unattached fatty acids present in a fat. Some unrefined oils may contain as much as several percent free fatty acids. The levels of free fatty acids are reduced in the refining process. (See Chapter VI.) Fully refined fats and oils usually have a free fatty acid content of less than 0.1%.

3. Phosphatides. Phosphatides, also known as phospholipids, consist of an alcohol (usually glycerol) combined with fatty acids, and a phosphate ester. The majority of the phosphatides are removed from oil during the degumming and refining operations. Phosphatides are an important source of natural emulsifiers marketed as lecithin.

4. Sterols. Sterols are found in both animal fats and vegetable oils, but there are substantial biological differences. Cholesterol is the primary animal fat sterol and is found in vegetable oils in only trace amounts. Vegetable oil sterols and plant sterols are collectively called "phytosterols." Stigmasterol and sitosterol are the best-known vegetable oil sterols. Sitosterol has been shown to reduce both serum and LDL cholesterol when incorporated into margarines, margarine spreads, salad dressings and various other food products to provide a convenient mode of delivery for consumers who choose to leverage phytosterols as a component of their personal plan to manage serum cholesterol levels. The type and amount of vegetable oil sterols vary with the source of the oil.

5. Tocopherols and Tocotrienols. Tocopherols and tocotrienols are important minor constituents of most vegetable fats. They serve as antioxidants to retard rancidity and as sources of the essential nutrient vitamin E. The common types of tocopherols and tocotrienols are alpha (α), beta (β), gamma (γ), and delta (δ). They vary in antioxidation and vitamin E activity. Among tocopherols, alpha-tocopherol has the highest vitamin E activity and the lowest antioxidant activity. Delta tocopherol has the highest antioxidant activity. Tocopherols which occur naturally in most vegetable oils are partially removed during processing. Corn and soybean oils contain the highest levels. Tocopherols are not present in appreciable amounts in animal fats. Tocotrienols are mainly present in palm oil, but can also be found in rice bran and wheat germ oils.

6. Pigments. Carotenoids are yellow to deep red color materials that occur naturally in fats and oils. They consist mainly of carotenes such as lycopene, and xanthophylls such as lutein. Palm oil contains the highest concentration of carotene. Chlorophyll is the green coloring matter of plants which plays an essential role in photosynthesis. Canola oil contains the highest levels of chlorophyll among common vegetable oils. At times, the naturally occurring level of chlorophyll in oils may cause the oils to have a green tinge. Gossypol is a pigment found only in cottonseed oil. The levels of most of these color bodies are reduced during the normal processing of oils to give them acceptable color, flavor, and stability.

7. Fatty Alcohols. Long chain alcohols are of little importance in most edible fats. A small amount esterified with fatty acids is present in waxes found in some vegetable oils. Larger quantities are found in some marine oils.

Table I provides a comparison of some of the non-triglyceride components of various crude oils.

TABLE I

Typical Non-Triglyceride Components of Crude Fats and Oils

 

Fat or Oil Phosphatides
(%)
Sterols
(ppm)
Cholesterol
(ppm)
Tocopherols
(ppm)
Tocotrienols
(ppm)
Soybean 2.2 ± 1.0 2965 ± 1125 26 ± 7 1293 ± 300 86 ± 86
Canola 2.0 ± 1.0 8050 ± 3230 53 ± 27 692 ± 85 --
Corn 1.25 ± 0.25 15,050 ± 7100 57 ± 38 1477 ± 183 355 ± 355
Cottonseed 0.8 ± 0.1 4560 ± 1870 68 ± 40 865 ± 35 30 ± 30
Sunflower 0.7 ± 0.2 3495 ± 1055 26 ± 18 738 ± 82 270 ± 270
Safflower 0.5 ± 0.1 2373 ± 278 7 ± 7 460 ± 230 15 ± 15
Peanut 0.35 ± 0.05 1878 ± 978 54 ± 54 482 ± 345 256 ± 216
Olive <0.1 100 <0.5 110 ± 40 89 ± 89
Palm 0.075 ± 0.025 2250 ± 250 16 ± 3 240 ± 60 560 ± 140
Tallow <0.07 1100 ± 300 1100 ± 300 -- --
Lard <0.05 1150 ± 50 3500 ± 500 -- --
Coconut <0.07 805 ± 335 15 ± 9 6 ± 3 49 ± 22
Palm Kernel <0.07 1100 ± 310 25 ± 15 3 ± 30 ± 30



O'Brien, R.D. Characterization of Fats and Oils, in Fats and Oils: Formulating and Processing for Applications, second edition. CRC Press, Boca Raton, p.8, 2004.

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