11. DEFINITION SOURCES, METHOD EXTRACTION, CHEMISTRY AND METHOD OF ANALYSIS OF LIPIDS

Introduction

Lipids are an important group of naturally occurring compounds that include fats, oils, waxes, phospholipids and steroids. They are insoluble in water but soluble in organic solvents such as ether, chloroform and benzene. Lipids play essential roles in energy storage, cell membrane structure and absorption of fat-soluble vitamins. Many crude drugs contain fixed oils and fats that are useful in pharmacy and industry.

Definition of Lipids

Lipids are organic compounds composed mainly of carbon, hydrogen and oxygen. Unlike carbohydrates, they contain a much lower proportion of oxygen. They are esters of fatty acids with glycerol or other alcohols. Lipids are hydrophobic or amphipathic substances and form an essential part of living cells.

Sources of Lipids

1. Plant Sources

  • Seeds: castor, mustard, linseed, groundnut.
  • Fruits: olive, palm kernel, coconut.
  • Nuts: almond, walnut.

2. Animal Sources

  • Fish oils: cod liver oil, shark liver oil.
  • Animal fats: lard (pig fat), tallow (beef fat).
  • Dairy fats: butter fat, ghee.

3. Microbial Sources

  • Certain fungi and algae produce lipid-rich oils.

Methods of Extraction of Lipids

Lipids are extracted from plant or animal material using one of the following methods:

1. Mechanical Expression

Also called cold pressing or expeller pressing. Material is crushed and pressed to remove oil. Common for groundnut oil, coconut oil and sesame oil.

2. Solvent Extraction

Material is treated with organic solvents like hexane or petroleum ether. Solvent dissolves the oil, and the mixture is separated and evaporated to recover pure oil. Used for seeds with low oil content.

3. Supercritical CO2 Extraction

Uses carbon dioxide at high pressure. Produces high-quality oil with minimal impurities.

4. Rendering (Animal Sources)

An animal tissue is heated, and melted fat is separated. Used for preparation of lard and tallow.

Chemistry of Lipids

1. Fatty Acids

These are long-chain carboxylic acids. They can be:

  • Saturated fatty acids: No double bonds (e.g., palmitic acid, stearic acid).
  • Unsaturated fatty acids: One or more double bonds (e.g., oleic, linoleic, linolenic acids).

2. Simple Lipids

  • Fats and oils: Esters of fatty acids with glycerol, also called triglycerides.
  • Waxes: Esters of fatty acids with long-chain alcohols.

3. Compound Lipids

  • Phospholipids: Contain phosphate group (e.g., lecithin).
  • Glycolipids: Contain carbohydrate groups.

4. Derived Lipids

  • Fatty acids, glycerol, steroids, fat-soluble vitamins (A, D, E, K).

Identification and Analysis of Lipids

Several analytical tests are used to check the purity and quality of fixed oils and fats.

1. Acid Value

  • Measures free fatty acids present in the oil.
  • Higher acid value indicates rancidity or decomposition.
  • Defined as the mg of KOH required to neutralise free fatty acids in 1 g of fat.

2. Saponification Value

  • Indicates the average molecular weight of fatty acids.
  • High saponification value = short-chain fatty acids.
  • Defined as mg of KOH required to saponify 1 g of fat.

3. Iodine Value

  • Measures degree of unsaturation.
  • Higher iodine value = more unsaturated fatty acids.
  • Useful for classifying drying, semi-drying and non-drying oils.

4. Peroxide Value

  • Indicates oxidation level.
  • High value shows rancidity.

5. Reichert-Meissl (R.M.) Value

  • Measures volatile short-chain fatty acids in fats like butter.

6. Acetyl Value

  • Measures hydroxyl groups in oils.

7. Unsaponifiable Matter

  • Portion of oil that does not form soap—includes sterols, vitamins and hydrocarbons.
  • Important for purity testing.

Rancidity of Lipids

Lipids may undergo deterioration known as rancidity.

Types

  • Oxidative rancidity: Due to oxidation of unsaturated fatty acids.
  • Hydrolytic rancidity: Due to breakdown of fats by moisture or enzymes.

Prevention

  • Store oils in airtight containers away from light.
  • Add antioxidants like BHA or vitamin E.

Applications of Lipids in Pharmacy

  • Used as emollients and ointment bases.
  • Serve as carriers for fat-soluble vitamins.
  • Used in soft-gel capsule formulation.
  • Serve as lubricants and binding agents.

Detailed Notes:

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