Fats and Oils (lipids)

Look at the chemical structure of lipidsKnow the difference between saturated and unsaturated fatsUnderstand the difference between cis and trans isomersUnderstand how trans-fats are madeConsider 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 groupsFatty acids are long chain carboxylic acids

DigestionIn 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 0 43 CoconutMyristic acid 14 0 54 NutmegPalmitic acid 16 0 62 Palm oilStearic acid 18 0 69 Animal FatPalmitoleic acid

16 1 0 Butter

Oleic acid 18 1 13 Olives and corn

Linoleic acid

Linolenic acid

18

18

2

3

-9

-17

Soybean, safflower, sunflowerCorn

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 pointsThis makes them more likely to deposit in your circulatory systemAnimal fats contain more saturated fatsPlant fats contain more unsaturated fatsHence 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 InuitHigh fish diet (salmon, char etc. oily fish)Very high blood cholesterol levels due to high meat dietLow levels of cardiovascular diseaseOmega 3 make blood platelets less stickyBlood does not get stuck where deposits of plaque have narrowed blood vesselsDoesn’t form clots leading to strokes or heart attacks.Too much and you may have difficulty stopping bleeding.

Cis and trans These relate to the unsaturated bonds in

fatty acids

What is the difference?

Cis and trans fats

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 shorterHave less surface area in contact between molecules so melt at lower tempsWhat does this remind us of?Therefore remain liquid in bodyTherefore easier to move away from blood vesselsBeing more curled up are higher densityThis 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 usesAs 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 fatsTrans fats have long chains like saturated fatty acids and behave like saturated fatty acidsStudies 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 triglyceridesThese are heated with a strong base such as sodium hydroxideNaOH makes solid soapsKOH makes more liquid soapsFat/oil + strong base = glycerol + fatty acid saltTripalmitin + NaOH = glycerol + sodium palmitate

Plenary questions1. All fats are made up of what?2. Why are they called triglycerides?3. Fats are a complex type of which organic chemical4. 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?