Lipids PDF

Elemental Composition of Lipids Lipids are composed of Carbon (C), Hydrogen (H), and Oxygen (O). Classification of Fatty Acids Fatty acids are long hydrocarbon chains with: ○ A carboxyl group (COOH) at one end ○ A methyl group (CH3) at the other end. The number of ca...

Elemental Composition of Lipids Lipids are composed of Carbon (C), Hydrogen (H), and Oxygen (O). Classification of Fatty Acids Fatty acids are long hydrocarbon chains with: ○ A carboxyl group (COOH) at one end ○ A methyl group (CH3) at the other end. The number of carbon atoms varies between fatty acids. General chemical formula: CH₃(CH₂) COOH. Fatty acids are classified based on their degree of saturation into three groups: 1. Saturated Fatty Acids 2. Monounsaturated Fatty Acids 3. Polyunsaturated Fatty Acids Saturation refers to the amount of hydrogen molecules present in a fatty acid. Distribution of Saturated, Monounsaturated, and Polyunsaturated Fatty Acids in Food All fats and oils are made up of a combination of saturated, monounsaturated, and polyunsaturated fatty acids. This combination determines the consistency, colour, taste, and texture of the fat or oil. The more hydrogen atoms a fatty acid has, the greater the degree of saturation. Essential Fatty Acids (EFAs) EFAs are fatty acids that cannot be manufactured by the body and must be obtained through food. Examples: ○ Linoleic acid (Omega-6) ○ Alpha-linolenic acid (Omega-3) Other polyunsaturated fatty acids (e.g., linolenic acid and arachidonic acid) are not considered essential as they can be synthesised in small amounts from linoleic acid. Sources of EFAs: Nuts Seeds Olive oil Oily fish Biological Functions of EFAs: 1. Aid in cell membrane formation, essential for growth. 2. Reduce the risk of coronary heart disease by: ○ Increasing HDL (high-density lipoprotein) to remove cholesterol. ○ Lowering LDL (low-density lipoprotein) to reduce cholesterol deposits. Omega-3 Fatty Acids These have a double bond between the third and fourth carbon atoms along their hydrocarbon chain. Two main types: 1. Eicosapentaenoic acid (EPA) 2. Docosahexaenoic acid (DHA) Sources of Omega-3 Fatty Acids: Oily fish Fish oils (e.g., cod liver oil) Eggs fortified with Omega-3 Seeds Nuts Biological Functions of Omega-3 Fatty Acids 1. Reduce the risk of coronary heart disease (CHD), heart attacks, and strokes by: ○ Raising HDL (high-density lipoprotein). ○ Lowering LDL (low-density lipoprotein). 2. Decrease blood viscosity, preventing clots or blockages in the coronary arteries. 3. Aid foetal brain development during pregnancy. 4. Help improve memory and cognitive functioning throughout life. Properties of Lipids 1. Solubility Lipids are insoluble in water. Soluble in solvents like ether and benzene. 2. Absorption of Flavours Lipids easily absorb flavours. Culinary applications: ○ Infused oils (e.g., chilli oil). ○ Flavoured butter (e.g., garlic butter). 3. Heating Lipids Melting (slip) point: ○ Solid fats melt when heated to 30–40°C. Smoke point: ○ At 200°C (fats) or 250°C (oils), lipids decompose. ○ Glycerol separates, forming acrolein, which produces a blue smoke and an acrid smell. Flash point: ○ Overheating to 310°C (fats) or 325°C (oils) emits a vapour that Emulsions An emulsion is a colloidal solution, where two immiscible liquids are forced to mix. Types of Emulsions: 1. Water in oil emulsions: ○ E.g., butter, margarine. ○ Tiny droplets of water are dispersed throughout the fat. 2. Oil in water emulsions: ○ E.g., milk, mayonnaise. ○ Tiny droplets of oil are dispersed throughout the water. Temporary vs Permanent Emulsions: Temporary emulsions: ○ Formed when immiscible liquids are shaken (e.g., vinegar and oil in vinaigrette). ○ Separate if left to stand. Permanent emulsions: ○ An emulsifier (e.g., lecithin in egg yolk) is added to prevent separation (e.g., mayonnaise).can ignite. Emulsifiers Molecules with a hydrophilic head (water-loving) and a hydrophobic tail (water-hating). An emulsifier prevents liquids from separating, creating a permanent emulsion. Culinary application: ○ Lecithin (naturally found in eggs) is used in mayonnaise. ○ Glycerol monostearate (GMS) is a commercial emulsifier used in ice cream. Stabilisers Long-chained molecules that help maintain emulsions by preventing oil and water droplets from separating. Culinary application: ○ Gums are used to stabilise yoghurt. ○ Gelatine is used to stabilise ice cream. Hydrogenation A process where hydrogen gas is forced through the double bond of an unsaturated oil in the presence of a nickel catalyst. This converts oil into a saturated solid fat. Culinary application: Used in margarine production. Rancidity Spoilage or decomposition of lipids, leading to unpleasant odour and taste. Types of rancidity: ○ Oxidative rancidity: Oxygen in air reacts with carbon in a double bond of unsaturated fat. ○ Hydrolytic rancidity: Enzymes or bacteria break down lipids into glycerol and fatty acids. Prevention: ○ Store in a cool, dark place. ○ Add antioxidants (e.g., vitamins A, C, E or BHA/BHT). Plasticity Refers to how soft, pliable, and spreadable a fat is at a given temperature. Determined by the degree of saturation: ○ More saturated fats = harder at room temperature. Culinary application: Low-saturation lipids (e.g., margarine) are used for creaming in baking. Biological Functions of Lipids 1. Energy: Supply heat and energy, maintaining body temperature and providing energy for activities. 2. Protection: Form a protective layer around delicate organs (e.g., kidneys). 3. Vitamin absorption: Supply fat-soluble vitamins (A, D, E, K). 4. Essential fatty acids: Provide EFAs (e.g., linoleic acid) that the body cannot make. 5. Insulation: Excess lipids stored as adipose tissue act as an energy reserve and insulate the body. Recommended Dietary Allowance (RDA) / Reference Intake (RI) Total fat intake for adults: No more than 70g/day. ○ Saturated fat: No more than 30g/day. ○ Women: No more than 20g/day. Energy Value of Lipids 1g of lipids provides 9 kcal of energy (37 kJ). Associated Dietary Disorders Consuming too many saturated fats and too few unsaturated fats can lead to: ○ Obesity ○ Coronary heart disease (CHD) ○ High cholesterol ○ Strokes Digestion of Lipids Lipids are broken down into glycerol and three fatty acid molecules through hydrolysis. Process of Digestion: 1. Mouth: Food is chewed into smaller pieces by teeth. 2. Stomach: Heat causes some fat to melt.  3. Liver: ○ Secretes bile into the duodenum (via the bile duct). ○ Bile emulsifies large fat molecules into smaller ones. 4. Pancreas: ○ Secretes pancreatic juice into the duodenum. ○ Contains lipase to break down lipids into fatty acids and glycerol. 5. Small Intestine: ○ Intestinal juice (in the ileum) contains lipase, further breaking down lipids. ○ Fatty acids and glycerol are now ready for absorption. Absorption and Utilisation of Lipids 1. Absorption: ○ Fatty acids and glycerol pass through the villi wall into lacteals (part of the lymphatic system). ○ Lymphatic system transports lipids to the thoracic duct, depositing them into the bloodstream via the subclavian vein (near the neck). 2. Utilisation: ○ In the liver and muscles, digested lipids are oxidised to produce: Heat Energy Cell membranes ○ Excess lipids are stored as adipose tissue under the skin, acting as insulation and energy reserves.