Lipids and Fatty Acids Overview

Elemental Composition of Lipids

• Lipids are composed of carbon (C), hydrogen (H), and oxygen (O).

Chemical Structure of Lipids

• Lipids are composed of triglycerides.
• A triglyceride contains one glycerol molecule and three fatty acid molecules.
• Glycerol is a trihydric alcohol with three hydroxyl (OH) groups.
• A fatty acid is an organic compound represented by the formula R-COOH. The R represents the hydrocarbon chain.
• Each hydroxyl group of glycerol combines with hydrogens from three fatty acids, resulting in the loss of three water molecules (condensation reaction).

Classification of Fatty Acids

• Fatty acids are long hydrocarbon chains with a carboxyl group (COOH) at one end and a methyl group (CH3) at the other.
• The number of carbon atoms varies between fatty acids.
• General chemical formula: CH3(CH2)nCOOH
• Fatty acids are categorized by their degree of saturation:
  • Saturated fatty acids
  • Monounsaturated fatty acids
  • Polyunsaturated fatty acids
• Saturation refers to the amount of hydrogen molecules present in a fatty acid.

Saturated Fatty Acids

• Each carbon atom is fully saturated with hydrogen atoms.
• No double bonds between carbon atoms.
• Solid at room temperature (high melting point).
• Examples include butyric acid (in butter), stearic acid (in meat).

Monounsaturated Fatty Acids

• Each carbon atom is not fully saturated with hydrogen atoms.
• One double bond between carbon atoms.
• Soft or liquid at room temperature (low melting point).
• Example includes oleic acid (in olive oil).

Polyunsaturated Fatty Acids

• Each carbon atom is not fully saturated with hydrogen atoms.
• More than one double bond between carbon atoms.
• Soft or liquid at room temperature (lowest melting point).
• Examples include alpha-linolenic acid, linoleic acid, arachidonic acid.

Essential Fatty Acids (EFAs)

• EFAs are fatty acids that the body cannot manufacture and must be obtained through food.
• Examples include linoleic acid (Omega-6), alpha-linolenic acid (Omega-3).
• Other polyunsaturated fatty acids can be synthesized from linoleic acid.

Sources of EFAs

• Nuts, seeds, olive oil, oily fish.

Biological Functions of EFAs

• Aid in cell membrane formation (essential for growth).
• Reduce the risk of coronary heart disease by increasing HDL (high-density lipoprotein) and lowering LDL (low-density lipoprotein).
• Decrease blood viscosity, preventing clots.
• Aid foetal brain development during pregnancy.
• Improve memory and cognitive function throughout life.

Omega-3 Fatty Acids

• Have a double bond between the third and fourth carbon atoms along the hydrocarbon chain.
• Two main types: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Cis and Trans Fatty Acids

• Cis fatty acids: Hydrogen atoms on the same side of the double bond.
• Trans fatty acids: Hydrogen atoms on opposite sides of the double bond.
• Cis fatty acids are naturally occurring in foods like olive oil and oily fish.
• Trans fatty acids are formed from cis fatty acids during heating or industrial processing (e.g., margarine).
• Trans fatty acids are generally considered less healthy than cis fatty acids.

Classification of Lipids by Source

• Animal fats are mainly saturated.
• Plant sources are mainly unsaturated.
• Marine sources are mainly polyunsaturated.

Properties of Lipids

• Solubility: Insoluble in water, soluble in solvents like ether and benzene.
• Flavor Absorption: Lipids easily absorb flavors.
• Heating: Melting points vary by type; decomposition occurs at higher temperatures.
• Emulsions: Mixture of immiscible liquids; temporary emulsions separate while permanent emulsions remain mixed (e.g., mayonnaise).

Emulsifiers

• Molecules with hydrophilic and hydrophobic properties preventing liquid separation in emulsion (e.g., lecithin, glycerol monostearate).
• Culinary use: Mayonnaise, ice cream.

Stabilisers

• Long-chained molecules maintaining emulsion stability (e.g., gums, gelatin).
• Culinary use: Yogurt, ice cream.

Hydrogenation

• Process of adding hydrogen to unsaturated fats.
• Converts oil into saturated fats (e.g., margarine production).

Rancidity

• Spoilage/decomposition of lipids (unpleasant odour/taste).
• Types include oxidative (oxygen reaction) and hydrolytic (enzyme/bacteria breakdown).
• Prevention methods (storage, antioxidants).

Plasticity

• Softening, pliability of fats at different temperatures.
• Depends on saturation levels (high saturation = harder).

Biological Functions of Lipids (Summary)

• Energy supply, body temperature maintenance, protection of organs, vitamin absorption, insulation, and essential fatty acid provision.

Dietary Allowance

• Adults: up to 70g total fat, up to 30g saturated fat per day.
• Women: up to 20g saturated fat per day.

Associated Dietary Disorders

• Consumption of too many saturated fats and fewer unsaturated fats leads to obesity, coronary heart disease (CHD), high cholesterol, strokes.

Digestion of Lipids

• Lipids are broken down into glycerol and fatty acids through hydrolysis.
• Digestion begins in the mouth (chewing), continues in the stomach (heating).

Absorption and Utilization of Lipids

• Fatty acids and glycerol are absorbed by the lymphatic system.
• Digested lipids are utilized to produce energy, cell membranes and stored as adipose tissue.