Why do fatty acids have a major effect on the properties of fats and oils?

Fatty acids are the primary components of fats and oils, accounting for 94 to 96 percent of their total weight. Because they constitute the reactive portion of triglyceride molecules, their chemical structure—specifically chain length and the degree of unsaturation—dictates the physical and chemical properties of the fat or oil.1

Physical Properties

The physical state of a fat at room temperature is largely determined by the composition of its fatty acids:23
* Saturation: Fats containing a high proportion of saturated fatty acids (which have no double bonds) tend to be solid at room temperature, as these molecules have higher melting points.21
* Unsaturation: Fats dominated by unsaturated fatty acids (containing one or more double bonds) are typically liquid oils. As the number of double bonds increases, the melting point decreases.2314
* Chain Length: In saturated acids, melting points rise as the hydrocarbon chain length increases.14

Chemical Properties

Fatty acids also influence chemical reactivity. The hydrocarbon chain is generally resistant to attack, but carbon-carbon double bonds are sites of high reactivity. These bonds are susceptible to oxidation, which can lead to rancidity. Consequently, the food industry uses hydrogenation to convert unsaturated fatty acids into more stable, saturated forms.1523