Fish Nutrition and Feed Technology (2+1)

Unit 4 - Lipids

4.4. Fatty acid structure and classification

Over 40 different fatty acids are known to occur in nature. They all can be represented by the general formula;

CH₃ (CH₂)_n COOH

where n = 0 in acetic acid, n = 1 in propionic acid, n = 2 in butyric acid, etc. up to n = 24 (where n is usually an even number).

Most naturally occurring fatty acids contain a single COOH group and a straight unbranched carbon (C) chain, which may in turn contain no double bond (saturated fatty acid), a single double bond (mono-unsaturated fatty acid), more than two double bond (polyunsaturated fatty acids, PUFA) or more than four double bonds (highly unsaturated fatty acids, HUFA). The degree of unsaturation will greatly influence the physical properties of the fats. In general unsaturated fatty acids are more chemically reactive and have lower melting points than the corresponding saturated fatty acids. Examples of saturated and unsaturated fatty acids are given below.

* Figures in parentheses indicate Number of carbon (C) atoms: number of double bonds and position of the first double bond counting from the methyl (CH3) end of the fatty acid.

The polyunsaturated fatty acids (PUFA) may be divided into three major families; the oleic (n-9) series, the linoleic (n-6) series, and the linolenic (n-3) series; the family names representing the shortest chain member of the group, with other family members being derived from these three basic groups.

• Phospholipids
• Glycolipids
• Waxes