Fats and Oils (lipids) Look at the chemical structure of lipids Know the difference between saturated and unsaturated fats Understand the difference between cis and trans isomers Understand how trans-fats are made Consider health issues around fat consumption. Saponification

Sources of fats and oils in our diets

What are lipids They are esters of fatty acids and glycerol. Three fatty acids are combined to one glycerol to make what is known as a triglyceride. Glycerol is a triol (an alcohol made with three hydroxyl groups Fatty acids are long chain carboxylic acids

Digestion In the digestive system enzymes hydrate (add water) to break the bonds and create a triol: glycerol and three fatty acids

Some chemistry of common fatty acids Name Carbon atoms Double bonds Melting point (C) Source Lauric acid 12 43 Coconut Myristic acid 14 54 Nutmeg Palmitic acid 16 62 Palm oil Stearic acid 18 69 Animal Fat Palmitoleic acid 1 Butter Oleic acid 13 Olives and corn Linoleic acid Linolenic acid 2 3 -9 -17 Soybean, safflower, sunflower Corn What patterns do you observe?

Saturated and unsaturated fatty acids What is the difference?

Write their condensed structural formulae

Dietary advice Saturated fats pack together more tightly. Therefore they have higher melting points This makes them more likely to deposit in your circulatory system Animal fats contain more saturated fats Plant fats contain more unsaturated fats Hence plant fats are healthier

Dietary advice Which would you expect to be the most/least healthy fats here?

Omega 3 and omega 6 acids These are considered healthy Low risk of disease of circulatory system Unsaturated fats Common in oily fish Omega 6 1st double bond links carbon 6 – 7 Omega 3 1st double bond links carbon 3 – 4

Health benefits of omega 3 fatty acids Noticed in Inuit High fish diet (salmon, char etc. oily fish) Very high blood cholesterol levels due to high meat diet Low levels of cardiovascular disease Omega 3 make blood platelets less sticky Blood does not get stuck where deposits of plaque have narrowed blood vessels Doesn’t form clots leading to strokes or heart attacks. Too much and you may have difficulty stopping bleeding.

Cis and trans What is the difference? These relate to the unsaturated bonds in fatty acids What is the difference?

Cis and trans fats Cis bonds make fatty acid chains bend Trans fats produced by hydrogenation of unsaturated fatty acids Trans fats normally man made Naturally occurring fatty acids normally cis This affects their properties Trans bonds make fatty acid chains long and straight. Cis bonds make fatty acid chains bend

Why are cis better for you. Cis are kinked so shorter Have less surface area in contact between molecules so melt at lower temps What does this remind us of? Therefore remain liquid in body Therefore easier to move away from blood vessels Being more curled up are higher density This is why high density cholesterol is better than low density cholesterol.

In view of this, why do we hydrogenate unsaturated fats The aim is to turn liquids into soft solids such as spreadable butters and margarines etc. These soft solids have many more industrial food uses As we hydrogenate unsaturated fats double bonds are converted to single bonds

Hydrogenation continued This process is not fully completed because completely hydrogenated fats are very brittle and of no use. Seen as beneficial as the end products from hydrogenated vegetable oils do not contain cholesterol like animal fats would, but have similar useful physical properties

Creating Trans fats Hydrogenation converts some cis to trans bonds Partially or fully hydrogenated fats in foods will contain trans fats Trans fats have long chains like saturated fatty acids and behave like saturated fatty acids Studies suggest high intake of trans fats lowers levels of good HDL-cholesterol. Thus linked to increased risk of heart disease.

Saponification Soap is made from fatty acids or triglycerides These are heated with a strong base such as sodium hydroxide NaOH makes solid soaps KOH makes more liquid soaps Fat/oil + strong base = glycerol + fatty acid salt Tripalmitin + NaOH = glycerol + sodium palmitate

Plenary questions 1. All fats are made up of what? 2. Why are they called triglycerides? 3. Fats are a complex type of which organic chemical 4. What is meant by cis and trans isomers? 5. How do cis and trans bonds affect the structure of fats? 6. What a re polyunsaturated fats? 7. What features do they have that is thought to make them less harmful? 8. What observation brought to light the value of omega 3?