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Lipids
| Question | Answer |
|---|---|
| Chemical composition | The formation of a Triglyceride ❖ A triglyceride is formed when one glycerol molecule joins with three fatty acids to produce a triglyceride and 3 water molecules ❖ Water is eliminated (condensation reaction) |
| Fatty acids | Fatty acids are long carbon chains with CH3 (methyl group) at one end and COOH (carboxyl group) at the other end. |
| Types of fatty acids | • Saturated fatty acids •Monounsaturated fatty acids (mono = one) •polyunsaturated fatty acids (poly = many) The number of carbon atoms differs with each fatty acid |
| Saturated fatty acids | Each carbon atom has its full amount of hydrogen. There are no double bonds present between the carbon atoms . They are generally solid at room temperature. They are generally from animal sources. •Butyric Acid in butter • Stearic Acid in meat |
| Monounsaturated fatty acids | Each carbon atom is not saturated with hydrogen . There is one double bond present. These fatty acids are soft or liquid at room temperature . They originate from plant sources •Oleic acid found in olive oil |
| Polyunsaturated fatty acids | Each carbon atom is not saturated with hydrogen .There is more than one double bond present. Fatty acids are soft/liquid at room temp. They are from plant/marine sources. • linoleic acid in nuts • linolenic acid in seeds • Arachidonic acid in o |
| Essential fatty acids | Cannot be manufactured in the body and must be supplied by the diet. • These include linoleic acid and alpha-linolenic acid Sources are nuts, seeds, olive oil and oily fish |
| Functions of essential fatty acids | •Build cell membranes • Counteract the hardening effect of cholesterol in the arteries • Help prevent CHD |
| Omega 3 | These are polyunsaturated fatty acids • Omega 3 relates to the positioning of the double bond • The double bond is between the 3rd and 4th carbon atom counting from the methyl end. Sources: Oily Fish – Salmon, herring, nuts, seeds, soya beans, |
| Benefits of omega 3 | • Reduced risk of heart attack, strokes, circulatory diseases and formation of blood clots. Increase HDL cholesterol levels. • It is also associated with healthy brain activity & memory function |
| Cis and trans fatty acids | Cis and trans fatty acids are based on the position of the hydrogen atoms at the carbon double bond of an unsaturated fat |
| Cis fatty acids | Cis fatty acids occur when the hydrogen atoms are at the same side of the carbon double bond • Occur naturally in foods e.g. oily fish, olive oil |
| Trans fatty acids | Trans fatty acids occur when hydrogen atoms are on the opposite side of the carbon double bond . Occur due to heating oils at high temperatures & due to hydrogenation • E.g. Hard margarine, pastries |
| Negatives on trans fatty acids | Trans fatty acids are thought to increase the risk of coronary heart disease (CHD) Tests have shown that: • they raise LDL or bad cholesterol • reduce HDL or good cholesterol |
| Melting point | Solid fats melt when heated. Water boils and evaporates at 100°C |
| Smoke point | When over heated they decompose . The glycerol breaks from the fatty acids . Glycerol changes to acrolein resulting in – A blue haze rising A bitter unpleasant smell Smoke point for fats is 200°C Oils is 250°C • Reusing lipids will lower the s |
| Flash point | When lipids are greatly over heated a vapour rises which can spontaneously burst into flames • Flash point for fats is 310°C Oils is 325°C |
| Ability to form emulsions | An emulsion is when 2 immiscible forced together e.g. oil and water, are forced to do so. Can be temporaryorCan be permanent: by the addition of an emulsifier. An emulsifier contains a hydrophilic head and a hydrophobic end . Eg lecithin for may |
| Working principle of an emulsion | The hydrophilic head attaches to water, while the hydrophobic tail attaches to the oil. |
| Plasticity | how easy it is to cream or spread a lipid. Fats that have plasticity are – Soft and pliable e.g. Soft margarine – Better for creaming and spreading Most animal fats do not have great plasticity, they are hard & difficult to spread e.g. butter |
| Rancidity | This describes the spoilage of fats – when fats ‘go off’ they are rancid |
| Oxidative rancidity | • This happens when oxygen in the air combines with unsaturated fatty acids (at the carbon to carbon double bond) • It happens more easily in warm, bright conditions |
| Hydrolytic rancidity | • This is caused by enzymes or bacteria, which break down the lipid into fatty acids and glycerol. • This sometimes occurs in a freezer |
| Hydrogenation | This occurs when hydrogen is forced through oils to make them solid fats in the presence of a nickel catalyst . The hydrogen combines with the carbon atoms at the double bond of an unsaturated fatty acid and makes it hard •eg margarine |
| Biological functions of lipids | Supply body with heat / energy • Form protective layer around delicate organs • Supply body with fat soluble vitamins: A, D, E and K • Provide body with essential fatty acids • Excess lipids insulates body and acts as energy reserve |
| Digestion of lipids | Liver: Produces bile, contains salts Bile salts break lipids down into emulsified fats then pancreas: contains pancreatic lipase. This lipase breaks fats into 1 glycerol molecule and 3 fatty acids. Illeum: contain intestinal lipase= 1 glycerol |
Created by:
Caoimhek
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