Unsaturated marine oils

In the past various marine oils were used in biscuits but this practice had now ceased. Most biscuits contain vegetable fats. It was common to use hydrogenated fat in biscuits because vegetable oils were too soft physically and too unsaturated to be stable against oxidation. If an unsaturated fat is hydrogenated until it is completely saturated then a saturated fat results however, if it is only partially hydrogenated a partially hydrogenated fat with several double bonds is produced. 

PALMITOLE1C ACID. [CAS 373-49-9], Also called dr-9-hexadec-anoic acid, formula CH3 (CH2)5CH CH(CHi>7COOH. This is an unsaturated fatty acid found in nearly every fat, especially in marine oils (15-20%i. At room temperature, it is a colorless liquid. Insoluble in water soluble in alcohol and ether mp 1.0°C bp 140-141°C (5 millimeters pressure). Combustible. Palmitoleic acid is used in organic synthesis, and as a standard in chromatographic analysis. See also Vegetable Oils (Edible). 

Marine oils also contain a wide variety of fatty acids. They are high in unsaturated fatty acids, especially those unsaturated acids with long chains containing 20 or 22 carbons or more. Several of these fatty acids, including eicosapen-taenoic acid (EPA) and docosahex-aenoic acid (DHA), have recently re-... 

Marine oils have also been found to contain a large number of component fatty acids. Ackman (1972) has reported as many as 50 or 60 components. Only about 14 of these are of importance in terms of weight percent of the total. These consist of relatively 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. 

Composition of fatty acids. The saturated and unsaturated fatty acids with 8 to 24 carbon atoms in animal fats, vegetable oils, marine oils, and fatty acids are quantitatively determined by gas chromatography (GC) after conversion to their methyl ester forms. However, free fatty acid analysis is also possible by using specially selected stationary solid... 

A marine oil typically contains some 40 different fatty acids, with carbon numbers varying from 10 to 24, which results in many different TAGs with the same carbon number, but with different levels of unsaturation (11). The fatty acids... 

Further interest in fish oils has been stimulated because of the association of the long-chain highly unsaturated acids, 20 5 and 22 6 with the alleviation of atherosclerosis (Dyerberg et ai, 1978 Barlow, 1980). Marine oils are however partially hydrogenated in order to obtain fats of adequate oxidative stability for conventional food application in margarine and shortenings. Industrial uses include soap, paints, varnishes, printing inks, leather treatment, water repellants and plasticizers. 

The fact that the marine oils are highly unsaturated has the consequence that they are in the liquid form even at low temperature. Hydrogenation makes the lipids solid. The major problem in utilising the marine oils in their liquid form is that they oxidise easily, producing a pronounced unpleasant fishy smell and taste (Meijboom and Stroink, 1972). This makes the oils unsuitable for food use. 

It is almost certain that the oxidation problem will find a solution, making it possible to use the marine oils as valuable ingredients in a variety of foods. The unsaturated nature further makes it possible to use the oils in products that are to be liquid even at low temperatures, for example salad dressings, or in products required to have a soft texture at low temperatures (Hsieh and Regenstein, 1991). 

The major contributions of saturated fatty acids originates mainly from vegetable oils such as coconut and palm kernels. The animal fats with the exception of marine oils contain large amounts of saturated fatty acids butterfat (63%), beef tallow (46%) and lard (42%). Marine oils, besides containing mono-unsaturated fatty acids, also contain long chain fatty acids with 20 carbon atoms and 4-6 double bonds. These are discussed in chapter 10. 

One attempt to classify fish fats (Lambertsen, 1978) is exemplified in Table 10.5. The percentages of as few as eight fatty acids of marine oils and lipids add up to about 80% of those present at 2-3% or more. Nutritionists may request 18 0, 18 2, 18 3 and 20 4, so 12 fatty acids have also been employed. Compared to lard, beef or sheep fats (see above), fish oils are considered highly unsaturated. One of the common trading standards of fish oils is the iodine value (IV). The iodine values of the monoethylenic fatty acids are 90 for 18 1 and 420 for 20 5n-3. Because of the extreme differences in IV for the typical two types of acids in Table 10.5, it was possible (Ackman, 1966) to develop an empirical formula percent polyunsaturated fatty acids = 10.7 + 0.337 (iodine value of oil—100). Table 10.6 shows the applicability of this formula. Since one of the objectives of the preparation of encapsulated fish oil products is to deliver 20 5n-3 and 22 6n-3 (Ackman et al., 1989 Sagredos, 1992), the iodine value is an easily utilized index of the suitability of raw materials for this or other uses. 

Sea mammals, whales and seals, and fish of the herring family serve as sources of marine oils. These oils t) ically contain highly unsaturated fatty acids with 4—6 allyl groups, such as (double bond positions are given in brackets) 18 4 (6, 9, 12, 15) 20 5 (5, 8, 11, 14, 17) 22 5 (7, 10, 13, 16, 19) and 22 6 (4, 7, 10, 13, 16, 19) (Table 14.4). Since these acids are readily susceptible to autoxidation, marine oils are not utilized directly as edible oils, but only after hydrogenation of double bonds and refining. 

Maleic anhydride is important as a chemical hecause it polymerizes with other monomers while retaining the double bond, as in unsaturated polyester resins. These resins, which represent the largest end use of maleic anhydride, are employed primarily in fiber-reinforced plastics for the construction, marine, and transportation industries. Maleic anhydride can also modify drying oils such as linseed and sunflower. 

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