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Questions and Answers
What is the acid number a measure of in fats and oils?
What is the acid number a measure of in fats and oils?
What happens to oils when they undergo chemical or bacterial contamination?
What happens to oils when they undergo chemical or bacterial contamination?
What is the significance of a high acid number in oils?
What is the significance of a high acid number in oils?
What is the saponification number a measure of in fats and oils?
What is the saponification number a measure of in fats and oils?
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Which type of fat has a saponification number of 195-200?
Which type of fat has a saponification number of 195-200?
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What is the iodine number a measure of in fats and oils?
What is the iodine number a measure of in fats and oils?
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What is the relationship between the iodine number and the degree of unsaturation of fatty acids?
What is the relationship between the iodine number and the degree of unsaturation of fatty acids?
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What is the Reichert-Meissl (RM) number a measure of in fats and oils?
What is the Reichert-Meissl (RM) number a measure of in fats and oils?
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What is the unit of measurement for the Reichert-Meissl (RM) number?
What is the unit of measurement for the Reichert-Meissl (RM) number?
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Why is it important to determine the iodine number of fats and oils?
Why is it important to determine the iodine number of fats and oils?
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Study Notes
Lipid Chemistry
- Lipids are organic substances relatively insoluble in water but soluble in organic solvents like chloroform, ether, and benzene.
- Lipids are classified into three main categories: simple lipids, complex lipids, and derived lipids.
Simple Lipids
- Simple lipids are esters of fatty acids with various alcohols.
- They consist of long-chain fatty acids that may be either free or combined with an alcohol by ester linkage.
- Hydrolysis of simple lipids yields glycerol and fatty acids, sterols, and fatty acids, etc.
- Alcohols in simple lipids can be subclassified as:
- Neutral fats or oils (alcohol is glycerol)
- Waxes (alcohol is other than glycerol)
Neutral Fats or Oils
- Esters of fatty acids with glycerol.
- Triglycerides are esters of trihydric alcohol or glycerol with 3 fatty acids.
- Uncharged.
Waxes
- Esters of fatty acids with higher molecular weight monohydric alcohols.
- Examples: lanolin, beeswax, cerumen (earwax).
- Waxes are esters of higher fatty acids with long-chain monohydric alcohols.
- Contain about 12-32 carbon atoms.
Complex Lipids
- Esters of fatty acids with alcohol containing additional (prosthetic) groups, such as phosphoric acid, sugars, nitrogenous bases, or proteins.
- Subclassified according to the type of prosthetic group:
- Phospholipids
- Glycolipids
- Lipoproteins
Phospholipids
- Esters of fatty acids with alcohol and phosphoric acid.
- Frequently have nitrogen-containing bases.
- Phospholipids are major membrane lipids that consist of lipid bilayers.
- Classified based on the type of alcohol present:
- Glycerophospholipids (alcohol is glycerol)
- Sphingophospholipids (alcohol is sphingosine)
Functions of Phospholipids
- In association with proteins, phospholipids form the structural components of membranes and regulate membrane permeability.
- Participate in the absorption of fat from the intestine.
- Essential for the synthesis of different lipoproteins and thus participate in the transport of lipids.
- Accumulation of fat in the liver (fatty liver) can be prevented by phospholipids, hence they are regarded as lipotropic factors.
- Arachidonic acid, an unsaturated fatty acid liberated from phospholipids, serves as a precursor for the synthesis of eicosanoids.
Derived Lipids
- Derivatives obtained on the hydrolysis of group 1 and group 2 lipids, which possess the characteristics of lipids.
- Examples: fatty acids, steroids, cholesterol, and vitamins A and D.
Functions of Lipids
- Structural component of cell membranes.
- Storage form of energy.
- Precursor of many steroid hormones and vitamin D.
- Acts as thermal insulators in lipids.
- Helps in the absorption of fat-soluble vitamins.
- Acts as electric insulators in neurons.
Test for Purity of Fats and Oils
- Acid number: measures the number of milligrams of potassium hydroxide required to completely neutralize the free fatty acids present in 1 g of the oil or fat.
- Saponification number: measures the average molecular size of the fatty acids present.
- Iodine number: measures the relative unsaturation of fats and is directly proportional to the content of unsaturated fatty acids.
- Reichert-Meissl (RM) number: measures the number of ml 0.1 N KOH required to completely neutralize the soluble volatile fatty acids distilled from 5 g of fat.
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Description
Learn about the basics of lipid chemistry, including the definition and classification of lipids into simple, complex, and derived lipids.
