Triglycerides & Fatty acids
We eat fat and oil every day, they provide energy and building blocks of hormone to us.
Fats are those in semi-solid or solid form, e.g. lard, and Oils are those in liquid form. Most fats are from animal while most oils are from fruit or plant seed. Exceptions are coconut oil and palm oil which is from plant but they are in semi-solid form.
Triglycerides is the basic fat molecule of both edible fat and oil. Each fat molecule consists of three long chains with carbon backbone, called fatty acids, all attached to one glycerol molecule (See pictures below). These fatty acids determine the properties of the molecule hence the fat and oil formed.
Simplified triglyceride structure
Detail triglyceride structure
Fatty acids are characterised by two primary molecular properties:
- Their length (how many carbon atoms there are in the chain)
- Their double bonds (how many there are & where they appear in the chain)
Saturated fatty acid
A "saturated" fatty acid like stearic acid and palmitic acid has no double bond and every carbon atom in the chain is completely saturated with hydrogen atoms.
Stearic acid (18 carbons, no double bond)
(Black: Carbon atom, White: Hydrogen, Red: Oxygen)
Palmitic acid (16 carbons, no double bond)
You can see these saturated fatty acids have regular straight pattern of carbon backbone, i.e. the stearic acid and palmitic acid only differ in the length of carbon chain. The regular shape takes up less space and allow these fatty acids to arrange themselves closer together. As they are packed tightly, more energy (heat) is needed to separate them, so the saturated fats have higher melting point, and they are semi-solid/solid at room temperature. Therefore fats and oils such as butter and palm oil, which are high in saturated fatty acid tend to solid at room temperature.
Unsaturated fatty acid
An "unsaturated" fatty acid like oleic, linoleic and alpha-linolenic acid has at least one double bond within its carbon chain.
Formation of each double bond releases two hydrogen atoms from the chain, resulting in a fatty acid that is no longer fully saturated by hydrogen atoms.
Linoleic acid (18 carbons, 2 double bond)
Oleic acid (18 carbons, 1 double bond)
Alpha-Linoleic acid (18 carbons, 3 double bond)
Oleic has one double bond hence it is known as "mono-unsaturated".
Linoleate has more than one double bonds therefore it is known as "poly-unsaturated".
Unsaturated fatty acids are not packed efficiently due to the presence of double bonds. These doubles bonds almost always* produce kinks in the fatty acid that make the packing harder. It is like packing bendy straws in to a box, you cannot do it better than the straight straws. As a result, oils such as Olive oil, Sunflower oil and Canola oil tend to stay liquid at room temperature.
* Fatty acids with double bonds that not making a kinks is commonly known as "trans fats".