Fats are esters of high molecular weight containing fatty acids and glycerol. Glycerol is a trihydric alcohol and therefore one two or all the three hydroxyl groups (OH) can react with fatty acids forming mono, di or triglycerides respectively.
Alcohols commonly include Glycerol, Cholesterol and higher alcohols such as cetyl alcohol and myricyl alcohol.
- IUPAC name of the Glycerol is Propane-1,2,3-triol (or) 1,2,3-trihydroxy propane.
- Commercial name is Glycerine, which is using in automobile industry as lubricating agent (It reduces friction between two metal bodies).
- The other unsaturated alcohols are Phytol (in chlorophyll) and lycophyll pigments (in Tomato).
Table of Contents
Fatty acids are long-chain organic acids having usually from 4 to 24 carbon atoms; they have a single carboxyl group and a long, non-polar hydrocarbon ‘tail’, which gives most lipids their hydrophobic and oily or greasy nature. Fatty acids do not occur in free or uncombined state in cells or tissues but are present in covalently bound form in different classes of lipids.
The systematic nomenclature of the fatty acids is based on the Geneva system. The names of saturated fatty acids end with the suffix -anoic and those of unsaturated acids with the suffix -enoic.
The numbering should be should be start from Carboxyl group (C1 of the Head region). The Greek lettering should be start from first -CH2- group (C2 of the Tail region).
Classification of Fatty acids:
Fatty acids can be classified into 4 types:
- Saturated FA
- Unsaturated FA
- Hydroxy or Oxygenated FA
- Cyclic FA
1. Saturated Fatty acids (SFA)
- General formula is Cn H2n+1 COOH
- The SFA contains only single bond, which have no double bonds.
- SFA is found in both Plant and Animal Kingdom
- In animal fats, palmitic and stearic acids (C16 and C18) are the most abundantly found saturated fatty acids next in order are shorter chain fatty acids (C14 and C12) and longer chain fatty acids (C20,C22 and C24).
- Ten carbon FA are mainly present in Milk fat
- Some branched chain FA are Isopalmitic acid(C16) present in Wool fat, Anti-iso palmitic acid(C17) present in Wool fat, Tuberculostearic acid (C 19) present in Bacteria.
2. Unsaturated Fatty acids (USFA):
- The USFAs contain double bonds in their structure.
- Based on the presence of double bonds the USFA can be divided into 4 types, they are
A. Monoethenoid acids — These contain one double bond and conform to the general formula, CnH2n–1COOH. The common example is oleic acid.
B. Diethenoid acids — Two double bonds; CnH2n-3COOH; Linoleic acid.
C. Triethenoid acids — Three double bonds; CnH2n-5COOH; Linolenic acid.
D. Tetraethenoid acids — Four double bonds; CnH2n7COOH; Arachidonic acid
- In mammals, polyunsaturated FAs can have up to 22 carbon atoms and 6 double bonds, but in plants these acids do not exceed 18 carbon atoms and 4 double bonds.
- Human body can convert Stearic acid to Oleic acid by inserting a double bond but is incapable of inserting further double bonds so that the Oleic acid cannot be converted to either linoleic, linolenic or arachidonic acid.
- Vegetable oils contain two types of polyunsaturated fatty acids (PUFAs) – linoleic acid (lin with 2 double bonds) and (-linolenic acid (len with 3 double bonds).
- Biosynthesis of Eicosanoids
- All USFA are more stable in “Cis-configuration” than “Trans configuration”.
Double Bonding system:
- USFA have “Non-Conjugative double bonding system” (or) “Cumulative double bonding system”.
3. Hydroxy or Oxygenated Fatty acids:
- Some of the fatty acids have hydroxyl group in their structure.
- Examples are Ricinoleic acid (87%) in Caster oil, It is a C 18 acid with a double bond at C9 and an OH group on C12. Cerebronic acid, a C 24 acid obtained from animal lipid, is another important hydroxyl acid with an OH group on C2.
- A common oxygenated fatty acid, isolated from plants and bacterial lipids, is 9, 10- dihydroxystearic acid.
- Another example is 9, 10-epoxystearic acid is isolated from rust spore lipids (20%).
4. Cyclic Fatty Acids:
- These are in Cyclized form fatty acids.
- Examples are Chaulmoogra oil obtained from Hydnocarpus kurzil contains Hydnocarpic and Chaulmoogric acid.
- These two cyclized fatty acids are using for the treatment of Leprosy.
- Chaulmoogric acid has a cyclopentenyl ring in its 18-carbon structure.
- Other examples are lactobacillic acid, sterculic acid