Fat hardening (hydration)
The economic significance of fat hardening (hydration) is obvious from the raw materials that are available. Apart from coconut, palm seed oil and cocoa butter, all oils offered for sale in Europe are liquids and are, therefore, unsuitable as semi-solid fats for uses such as spreading on bread or for bakery products.
When oil is hydrated, hydrogen is attached to the double bond on unsaturated fatty acids, in the presence of catalysts (usually nickel) that speed up the reaction. Electrophilic addition of hydrogen is confined solely to unsaturated fatty acids and does not involve the trivalent fatty ester (glycerol). Oil hydration is influenced by time, temperature, hydrogen pressure, mass transport, the catalyst (type, state, concentration), substrate type and the manner in which the process is carried out.
As well as hydrogen, oxygen can also be added to polyunsaturated fatty acids. This occurs naturally as fats spoil (rancidity), but the process can be induced artificially by bubbling air into heated oil. The resultant peroxide compounds cause fatty acids to react further and to become polymers. These large, branched molecules give the oil high viscosity, which can be halted at any stage by adjusting blowing times. Blown oils are used as lubricants since they adhere well to metals.
Esterification alters the properties of fats and oils by redistributing fatty acids on the glycerol framework. During the esterification process, fats and oils are broken down briefly into their component parts, before being re-arranged and re-assembled to produce custom fats/oils for specific purposes.
Examples of this include special baking fats derived from palm seed oil and coconut oil. Esterification reactions are very slow. That is why strongly ionic catalysts, such as sodium, sodium hydroxide and sodium alcoholate, are added. Because of the large numbers of different fatty acids present in natural fats and oils, there are countless possible combinations, which is why fats and oils are used that feature certain glyceride classes in particular (e.g., oils with C8-C14 chain lengths ).