Plant Oils

pressing - the material is crushed and the oil is squeezed out, then in centrifuge (spinning in a container). the oil is at the top and the material at the bottom.

Steam Distillation - the material is warmed up gently, suspended over boiling water. the steam and oil condeses into a beaker.

in both of these processes - water and other impurities are removed leaving relatively pure oils

fats from animal sources eg lard, butter ect are solid oils and have similar chemical composition

both fats and oils are an important part of your diet if you body is to work properly. 1g of oil contains 34kJ of energy. 1g of carbohydrate contains 9.6kJ of energy.

important vitamins are supplied by oils such as a, d, e and k

using oil makes things taste nicer, but gives the food more calories. for example potatoes that are cooked in boiling vegetable oil have more calories but potatoes that are cooked in boiling water taste boring.

both vegetable oils and animal fats are quite complicated compounds containing things called fatty acids, these are compounds of the elements carbon, hydrogen and oxygen.

these fatty acids contain long chains of carbon atoms, aprox 16 atoms long.

some of these carbon chains contain double bonds and are called monounsaturates.

some contain no double bonds and are saturated.

some contain several double bonds and are polyunsated.

a carbon carbon double bond looks like c=c and a single bond looks like c-c

                                         animal fats                     vegetable oil

 examples                    butter, suet, lard                  sunflower oil, olive oil

chemical makeup       saturated                              mono/polyunsaturated

melting points            high - solid at room               low - liquid    at room        t                                        empreature                          tempreature

effects on health       heart disease, high         lowers blood preassure cholesterol, obesity, high blood preassure          lower cholesterol less risk of heart                                                                       heart     disease

bromine water can be used to test for double bonds, when added to an unsaturated fat it turns from a yellowy brown colour to colourless.

an alternative is iodine water

when added to  these substances the changes are:

• olive oil - decolourised
• lard - stay orange/brown
• palm oil - decolourised
• butter - stay orange/brown
• margerine - decolourised.

to test which substance has the most double bonds, bromine water is repetely added, the longer it takes of for the bromine water to stay orange/brown the more double bonds

the fatty acids in vegetable oil are usually polyunsaturated.

these fatty acids can be reacted with hydrogen in the presence of a nickel catalyst at a tempreature of 60degreesC ish - some of the double bonds will be broken.

getting rid of SOME of the bonds makes the oil harder and increases the melting point and turns it into a soft spread like margerine.

these margerines still contain one or more double bond so are often softer that animal fats and are thought to be healthier

Vegetable oil

margarine

butter

Double bonds

many

few

None

Amount of bromine water decolourised

lots

some

Little

Effects on health

mild

more

Lots

State at room temp.

liquid

Soft solid

Hard solid