ABSTRACT
Extraction and fractionation of fish oils has become a major area of research over the last 30 years because of the potential application of these extracts and fractions in the pharmaceutical, nutraceutical, and cosmetic industries. The major constituents of fish oils are triacylglycerides (TAGs). Minor components include free fatty acids, squalene, tocopherols, cholesterol, wax esters, sterol esters, phospholipids, diacylglycerides, diacylglycerol ethers, pigments, and vitamins A, D, and E. Oils of marine origin are significantly more complex than those from plants and terrestrial animals. The fatty acids that constitute TAGs in fish oils vary considerably according
to degree of unsaturation, variety of chain length, and number of isomeric compounds. TAGs are typically made up of straight-chain fatty acids containing from 12 to 24 or more carbons, with the degree of unsaturation varying from zero to six double bonds. Fish oils often contain more than 60 different fatty acids, including isomers, which differ according to the position of unsaturation within the carbon chain. The complex composition of fish oils makes them difficult to process to concentrate specific fatty acids. High levels of unsaturation make the use of high-temperature processing methods problematic because of the susceptibility of these compounds to oxidative and thermal degradation. The variability in fatty acid composition of fish oil is highly dependent on fish species, season, feeding habits, part of the fish used (e.g., liver or flesh), and catch location. Some fatty acid profiles of selected fish oils are shown in Table 5.1 [1], which shows that liver oil composition is usually less saturated than that of the flesh.
