5.1 - Oils and Fats

Formation and Importance of Oils and Fats

Oils and fats are esters formed when fatty acids react with glycerol, or propan-1,2,3-triol, in an esterification reaction.
One glycerol molecule reacts with three fatty acid molecules to form one fat molecule and three water molecules.
Fatty acids are long-chain carboxylic acids. Examples include palmitic acid, stearic acid and linoleic acid.
The hydrocarbon chains, represented by $R_{1}$ , $R_{2}$ and $R_{3}$ , may be identical or different. Their identities determine the properties of the oil or fat.
Oils and fats supply energy, insulate the body and help the absorption of vitamins A, D, E and K.

Aspect	Oils	Fats
Usual source	Plants	Animals
State at room temperature	Liquid	Solid
Melting point	Low	High
Main fatty-acid content	High percentage of unsaturated fatty acids	High percentage of saturated fatty acids
Example	Palm oil	Butter

Saturated fats contain saturated fatty acids such as palmitic, lauric and stearic acids. Their carbon chains contain only single covalent bonds.
Unsaturated fats contain unsaturated fatty acids such as oleic, linoleic and linolenic acids. Their carbon chains contain at least one carbon-carbon double bond.
Double bonds lower the melting point, so unsaturated fats tend to be liquids at room temperature.

Oils contain a high percentage of unsaturated fats. They can be converted to saturated fats by hydrogenation.
Hydrogen gas is passed through hot oil in the presence of nickel as a catalyst. Carbon-carbon double bonds open and hydrogen atoms add to the carbon chain.
Adding hydrogen increases molecular mass as well as melting and boiling points. This explains why margarine is solid at room temperature although it is produced from oil.
Each carbon-carbon double bond consumes one $H_{2}$ molecule; a fat molecule with three such bonds consumes three $H_{2}$ molecules.

Nutritional source: supplies energy and helps the absorption of vitamins A, D, E and K.
Biofuel: oils and fats can be converted into biodiesel for diesel engines.
Soap and personal care: they are raw materials for soap and products such as skin moisturisers.
Animal feed: they help fulfil the nutritional needs of livestock.
Excessive consumption can contribute to obesity and heart-related illness. Excessive animal fat or saturated fat intake raises the risk of arteriosclerosis.