Leaving Cert Home Ec: Lipids

Elements

Carbon

Hydrogen

Oxygen

Basic Structure

Triglyceride

(One glycerol and 3 fatty acids)

Classification

1. Saturated

2. Monounsaturated

3. Polyunsaturated

Saturated fatty acids

Have the maximum number of hydrogen atoms possible and no double bonds

Structure of saturated fatty acids

Contain Carboxyl group (COOH) and Methyl group (CH3)

sources of saturated fatty acids

Generally found in animal sources e.g....

-Butyric acid

-Stearic in meat

Monounsaturated fatty acids

Each carbon atom is not fully saturated with a full quota of hydrogen atoms, and there is one double bond between the carbon atoms.

structure of monounsaturated fatty acid

Contains carboxyl group (COOH) and methyl group (CH3)

sources of monounsaturated fatty acids

Generally found in plant and marine sources e.g...

-olive oil

-canola oil

-peanut oil

Polyunsaturated fatty acids

Each carbon atom is not fully saturated with its quota of hydrogen atoms and it contains more than one double bond

Structure of polyunsaturated fat

Contains carboxyl group (COOH) anf methyl group (CH3)

Sources of polyunsaturated fats

Generally found in plant or marine sources e.g...

-Linoleic acid in nuts

-Linoleic acid in seeds

-Arachidonic acid in oily fish

Cis and trans fatty acids

Monounsaturated and polyunsaturated fats can either be cis or trans fatty acids and the orientation of hydrogen atoms around the Carbon double bond is what distinguishes "cis" fatty acids from "trans" fatty acids.

Cis fatty acids

Hydrogen atoms are on the same side of the double bond (either above or below)

Sources of cis fatty acids

Naturally occurring in foods such as olive oil and oily fish

Health effects of cis fatty acids

Raise HDL (high density lipoprotein) and lower levels of LDL (low density lipoprotein) which is good for health

Trans fatty acids

Hydrogen atoms are on opposite sides of the double bond

Sources of trans fatty acids

-Formed from cis fatty acids during the heating or frying of oils at a high temperature

-Also present in foods that contain hydrogenated fats

Health effects of trans fatty acids

Generally bad for health as they lower HDL and higher LDL which increases risk of coronary heart disease

Essential fatty acids

Fatty acids that cannot be made by the body, so must be gotten from food sources

Sources of EFAs

Nuts

Seeds

Olive oil

Oily fish

Functions of EfAs

Cell membrane formation

Reduce risk of CHD (Coronary heart disease)

Omega-3 fatty acids

Have a double bond between the third and fourth carbon atoms along their hydrocarbon chain

Sources of Omega-3

Flaxseed oil

Walnuts

Fish oils e.g. Cod liver oil

Functions of Omega-3

Reduce the risk of coronary heart disease and strokes

Decrease the viscosity of blood

Aids foetal brain development

Properties of lipids

1.Solubility

2.Absorption of flavours

3.Heating lipids

4.Emulsions

5.Hydrogenation

6.Rancidity

7.Plasticity

1. Solubility

Lipids are insoluble in water, but soluble in other liquids such as ether and benzene

2. Absorption of flavours

Lipids absorb flavours easily

3. Heating lipids

-Melting point: Solid fats melt when heated to 30-40 degrees celsius

-Smoke point: If lipids are heated to 200 degrees they begin to decompose, cause the glycerol to separate from the fatty acids. Glycerol is then broken down to acrolein and produces blue smoke and an acrid smell.

-Flash point: Extreme overheating of lipids to 310 degrees causes a vapour to be emitted that can spontaneously ignite

4. Emulsions

An emulsion is a solution formed when to immiscible liquids are forced to mix together.

Two types: Water in oil emulsions or Oil in water emulsions

5. Hydrogenation

A process whereby hydrogen gas, in the presence of a nickel catalyst , is forced through the double bond of an unsaturated oil, converting the unsaturated oil into a solid, saturated fat.

6. Rancidity

Spoilage or decomposition of lipids which results in an unpleasant odor and taste.

Two types...

Oxidative rancidity: When oxygen in the air combines with the carbons in a double bond of an unsaturated fat.

Hydrolytic rancidity: When enzymes or bacteria break down lipids into glycerol and fatty acids

7. Plasticity

How soft, pliable and malleable a fat is at a given temperature. It is determined by the degree of saturation.

More saturation=More solid

Biological functions of lipids

-Supply body with heat and energy

-Protect delicate organs

-Supply body with fat soluble vitamins

-Excess lipids are stored as adipose tissue under the skin

RDA of lipids

70g per day (Mainly unsaturated)

Digestion of lipids

During digestion, water and enzymes break lipids into glycerol and 3 fatty acids.

This process is called hydrolysis

Mouth

Food is chewed into small pieces

Stomach

Heat within stomach causes the fat to melt

Liver

Secretes bile into duodenum which emulsifies large fat molecules to produce smaller molecules

Pancreas

Secretes pancreatic juice into duodenum which contains enzyme lipase. This begins to break down the lipids into fatty acids and glycerol

Small intestine

The ileum secretes intestinal juice also containing lipase which continues the breaking down of the lipids into their basic form

Absorption and utilisation of lipids

After digestion, the fatty acids and glycerol are ready to be absorbed by small intestine, They pass through wall of villi into lacteals, which forms part of the lymphatic system

Next step

The lymphatic system transports the digested lipids to the thoracic duct, where it is deposited into the bloodstream through the subclavian vein

Excess digested lipids

Stored as adipose tissue under the skin to insulate body and act as an energy reserve