General Veterinary Biochemistry

ISOMERISM IN UNSATURATED FATTY ACIDS

• Due to the presence of double bond, fatty acids exhibit geometrical isomerism, which depends on the orientation of groups around the double bond. The designation “cis” means that the acyl chains are on the same side. “Trans” means the acyl chains are on the opposite side of the double bond.
• The double bonds in most naturally occurring fatty acids are in the cis configuration. Cis and Trans isomers have different melting points and other physical constants. Trans fatty acids are stable but are injurious to health. Eg: The trans form of oleic acid (cis) is called elaidic acid.
• Trans fatty acids are formed when the vegetable oils are hydrogenated. For example in the manufacturing of margarine.
• Ruminant fat contains more trans long chain fatty acids than non-ruminants because rumen microbes isomerizes some plant cis long chain fatty acids to trans isomer.
• Trans fatty acids compete with essential fatty acids so there is reduction in the absorption of essential fatty acids, which may increase the symptoms of essential fatty acid deficiency.
•  They have structures similar to saturated fatty acids. Hence, they increase cholesterol level and the formation of atherosclerosis.