LIPIDS

© PDST Home Economics

Lipids

• The term lipids covers fats and oils

Fats= Solid at room temperatureOils = Liquid at room temperature

Elemental Composition

Recall the elemental composition ofcarbohydrates??? Carbon (C)Carbon (C) Hydrogen (H)Hydrogen (H) Oxygen (O)Oxygen (O)Note: These elements are found in different

proportions to carbohydrates.

Chemical Composition

• The formation of a Triglyceride A triglyceride is the chemical name given to a fat A triglyceride is formed when one glycerol

molecule joins with three fatty acids to produce a triglyceride and water

Water is eliminated (condensation reaction)

+

+

+

H20

H20

H20

+

+

+

Chemical Structure of LipidsChemical Structure of Lipids

Glycerol + 3 Fatty Acids = Triglyceride + Water

Chemical Structure of Lipids

• A Glycerol molecule has 3 Hydroxyl Groups (OH).• Every fatty acid has a Carboxyl Group at the end.• A Hydroxyl group from the Glycerol and a Hydrogen

atom from the end of the fatty acid break off and combine to form water (H2O)

• As a result the fatty acid becomes bonded to the glycerol.

• This happen for each of 3 fatty acids and 3 water molecules are released.

Chemical Structure of Lipids

Fatty Acids

• There are many different Fatty Acids but all have same basic structure.

• They are made of chains of carbon with a methyl group at one end (CH3) and a carboxyl group at the other end (COOH).

• What makes one fatty acid different from another is the length of the carbon chain

• For example: butyric acid has 2 carbons in the carbon chain whereas stearic acid has 18

Classification of Fatty Acids

• Fatty acids are long carbon chains with CH3 (methyl group) at one end and COOH (carboxyl group) at the other end.

• Fatty acids are classified into three groups 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 is saturated with hydrogen • There are no double bonds present between the

carbon atoms• They are generally solid at room temperature • They are generally from animal sources • Examples: Butyric Acid in butter and Stearic Acid

in meat

Structure of Saturated Fatty Acid

Monounsaturated Fatty Acid

• 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 • Example: oleic acid found in olive oil

Structure of Monounsaturated Fatty Acid

Polyunsaturated fatty acid

• Each carbon atom is not saturated with hydrogen• There is more than one double bond present• These fatty acids are soft or liquid at room

temperature • They originate from plant/marine sources • Examples include linoleic acid in corn oil and

linolenic acid in vegetable oil

Structure of Polyunsaturated Fatty Acid

Essential Fatty Acids

• Cannot be manufactured in the body and must be supplied by the diet.

• These include linoelic acidlinoelic acid found in corn oil, linolenic acidlinolenic acid found in vegetable oil, arachidonic arachidonic acidacid found in animal fat.

• Linoleic acid is the most important of these as linolenic acid and arachidonic acid can be manufactured from linoleic acid.

Functions of Essential Fatty Acids (EFA’s)

• Build cell membranes• Counteract the hardening effect of cholesterol in

the arteries • Help prevent CHD

Cis and Trans Fatty Acids

• Cis and trans fatty acids are based on the position of the hydrogen atomshydrogen atoms at the double bond

Cis Fatty Acids

• Cis fatty acids occur when the hydrogen atoms are at the same sidesame side of the double bond

C = C

H H

Trans Fatty Acids

• Trans fatty acids occur when hydrogen atoms are on the opposite sideopposite side of the double bond

H

C = C

H

A Closer look at Trans fatty Acids

• During cooking and processing Cis fatty acids are converted into trans fatty acids e.g. through the addition of hydrogen during margarine manufacturing (hydrogenation)

• Trans fatty acids are thought to increase the risk of coronary heart disease (CHD), in particular trans fatty acids that are produced synthetically

• Tests have shown that they raise the level of low density lipoproteins (LDL) or bad cholesterol and reduce high density lipoproteins (HDL) or good cholesterol

Effects of cholesterol on the artery

Sources of Trans fatty acids

Omega 3 Fatty Acids

• 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. • Omega 3 fatty acids are known as EPA

(eicosapentaenoic acids) and DHA (docoshexaenoic acids)

Omega 3 Fatty Acids

Sources:Sources: Oily Fish – Salmon, herring, mackerel, nuts, seeds, soya beans, supplementsBenefits: 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.

Properties of Lipids1. Solubility• Lipids are insoluble in water• Lipids are soluble in solvents

eg. Ether & benzene

2. Plasticity• A combination of saturated &

unsaturated fatty acids allows for shape & structure of the lipid

• This is useful in pastry making, e.g. Margarine is used in the creaming method

3. Hydrogenation• Hydrogenation occurs when

hydrogen is forced through the double bond of unsaturated fatty acids in the presence of a nickel catalyst

• This property is evident in the production of margarine

• A catalyst is a substance that speeds up or slows down a reaction without itself changing

Hydrogenation continued..

H H H H

- C = C- ++ H2 - - C = C -

H H

Properties of lipids cont...4. Affected by heat• There are varying temperatures that affect lipids (Fats

& oils)

Melting Point Smoke Point Flash Point

•Solid fats melt when heated•FATS: 30-40˚C

•Lipids begin to decompose to gylcerol & 3 fatty acids•A blue haze emerges•An acrid-smelling compound known as acrolein is present•FATS: 200˚C •OILS: 250˚C

•The decomposition of the lipids continues•Lipids spontaneously burst into flames•FATS: 310˚C•OILS: 325˚C

5. Rancidity• This is the term used to describe lipids when

they ‘go off’• There are two types of rancidity: these are

oxidative & hydrolytic• To prevent rancidity, store food correctly & use

an anti-oxidant• Anti-oxidants occur naturally in vitamins A,

C & E and artifically in BHA & BHT

Rancidity Cont...Oxidative Hydrolytic

•This form of rancidity occurs when oxygen is forced through the double bond of an unsaturated fatty acid. It is the most common form of rancidity H H H H -- C C -- + O2 -- C—C-- O O •Eg. Oil solidifying on a pan

•This form of rancidity occurs when enzymes & bacteria react with the lipid•This occurs most commonly in freezers when enzymes are not destroyed•It results in the triglycerides breaking down – flavour is altered

6. Emulsions• There are two types of emulsions: oil in water &

water in oil• When two immiscible liquids are forced together, an

emulsion is formed

1.1. A temporary emulsion A temporary emulsion occurs when oil and vinegar are forced together, e.g. French dressing – this is caused by shaking & will seperate on standing

2.2. A permanent emulsion A permanent emulsion occurs when oil & water are forced together in the presence of an emulsifier, eg. Mayonnaise (oil + water + emulsifier - lecithin in egg yolk) = Emulsion

• An emulsifier has two parts: a water -loving head (hydrophilic) & a water-hating tail (hydrophobic)

• Hydro: Water Philic: LovePhobic: Hate

Working Principle of an Emulsifier

Vinegar Oil Hydrophobic Hydrophilic tail head

• The hydrophilic head attaches to water, while the hydrophobic tail attaches to the oil

• The hydrophilic head attaches itself to the water molecule

• The hydrophobic tail attaches itself to the oil component of the emulsion

OIL WATER• Stabilisers are used to maintain an emulsion, eg. In

ice cream• An example of a stabiliser used in ice cream is

alginates (E400)Vinegar

Oil Stabiliser

Digestion of Lipids

Liver: Produces Bile, contains saltsBile Salts break lipids down into emulsified fats

Pancreas: Pancreatic Juice contains pancreatic lipase. This lipase breaks lipids into 1 glycerol molecule and 3 fatty acids

Illeum (small intestine): Intestinal juices contain intestinal lipase. This lipase continues breakdown of lipids into 1 glycerol molecule and 3 fatty acids

Organ/Organ/

GlandGland

Secretion Secretion EnzymeEnzyme SubstrateSubstrate ByBy

ProductProduct

Liver Bile Bile

Salts

Lipids Emulsified fats

Pancreas Pancreatic juices

Pancreatic lipase

Lipids Glycerol + 3 fatty acids

Illeum Intestinal Juice Intestinal Lipase

Lipids Glycerol + 3 fatty acids

Absorption of Lipids

• When digested the lipids (glycerol + 3 fatty acids) can be absorbed

• Absorption takes place in the lacteals in the villi of the small intestine

Absorption of Lipids

• Digested lipids are carried via the lymph system to the bloodstream at the subclavian vein in the neck.

Utilisation of Lipids

Lipids are oxidised in the liver and muscles to 1. Produce heat and energy 2. Form cell membranes

Excess lipids are stored in the adipose tissue underneath the skin. This

1. Insulates the body2. Acts as an energy reserve3. Protects delicate organs