Classification of Lipids

Simple Lipids
1. Triglycerides, neutral fats: Found in adipose tissue, butterfat, lard, suet, fish oils, olive oil, corn oil, etc. Esters of three molecules of fatty acids plus one molecule of glycerol; the fatty acid may all be different.
2. Waxes: beeswax, head oil of sperm whale, cerumen, carnauba oil, and lanolin. Composed of esters of fatty acids with alcohol other than glycerol; of industrial and medicinal importance.
Compound Lipids
1. Phospholipids (phosphatides): Found chiefly in animal tissues. Substituted fats, consisting of phosphatidic acid; composed of glycerol, fatty acids, and phosphoric acid bound in ester linkage to a nitrogenous base.
2. Lecithin: Found in brain, egg yolk, and organ meats. Phosphatidyl choline or serine; phosphatide linked to choline; a lipotropic agent; important in fat metabolism and transport; used as emulsigying agent in the food industry.
3. Cephalin: Occurs predominantly in nervous tissue. Phosphatidyl ethanolamine; phosphatide linage to serine or ethanolamine; plays a role in blood clotting.
4. Plasmalogen: Found in brain, heart, and muscle. Phosphatidal ethanolamine or choline; phosphatide containing an aliphatic aldehyde.
5. Lipositol: Found in brain, heart, kidneys, and plant tissues together with phytic acid. Phosphatidyl inositol; phosphatide linked to inositol; rapid synthesis and degradation in brain; evidence for role in cell transport processes.
6. Sphingomyelin: Found in nervous tissue, brain, and red blood cells. Sphingosine-containing phosphatide; yields fatty acids, choline, sphingosine, phosphoric acid, and no glycerol; source of phosphoric acid in body tissue.
7. Glycolipids:
  1. Cerebroside: myline sheaths of nerves, brain, and other tissues. Yields on hydrolysis of fatty acids, sphingosine, galactose (or glucose), but not fatty acids; includes kerasin and phrenosin.
  2. Ganglioside: brain, nerve tissue, and other selected tissues, notably spleen; contains a ceramide linked to hexose (glucose or galactose), neuraminic acid, sphingosine, and fatty acids.
  3. Sulfolipid: white matter of brain, liver, and testicle; also plant chloroplast. Sulfur-containing glycolipid; sulfate present in ester linkage to galactose.
  4. Proteolipids: brain and nerve tissue. Complexes of protein and lipids having solubility properties of lipids.
Terpenoids and Steroids
1. Terpenes: Found in essential oils, resin acids, rubber, plant pigments such as caotenese and lycopenes, Vitamin A, and camphor. Large group of compounds made up of repeating isoprene units; Vitamin A of nutritional interest; fat soluble Vitamin E and K, which are also related chemically to terpenes.
2. Sterols:
  1. Cholesterol: found in egg yolk, dairy products, and animal tissues. A consituent of bile acids and a precursor of Vitamin D.
  2. Ergosterol: found in plant tissues, yeast, and fungi. Converted to Vitamin D2 on irradiation.
  3. 7-dehydrocholesterol: found in animal tissues and underneath skin. Converted to D3 on irradiation.
3. Androgens and estrogens: (Sex hormones) Found in ovaries and testes.
4. Adrenal corticolsteroids: adrenal cortex, blood.
Derived lipids
1. Fatty acids: occur in plant and animal foods; also exhibit in complex forms with other substances. Obtained from hydrolysis of fats; usually contains an even number of carbon atoms and are straight chain derivatives.
  Classification of fatty acids is based on the length of the carbon chain (short, medium, or long); the number of double bonds (unsaturated, mono-, or polyunsaturated); or essentiality in the diet (essential or non-essential). A current designation is based on the position of the endmost double bond, counting from the methyl (CH3) carbon, called the omega end. The most important omega fatty acids are: Omega 6 – linolein and arachidonic acids and Omega 3 – linolenic, eicosapentaenoic, and docosahexaenoic acids.
  Sample nomenclature for fatty acids:
  - Butyric acid – 4:0
  - Palmitic acid – 16:0
  - Oleic acid – 18:1 (9)
  - Linoleic acid – 18:2 (9,12)
  - Linolenic acid – 18:3 (9,12,15)
  - Arachidonic acid – 20:4 (5,8,11,14)
  - Eicosapentaenoic acid – 20:5 (5,8,11,14,17)
  - Docosahexaenoic acid – 22:6 (4,7,10,13,16,19)

Classification of Lipids

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