The economic importance of hardening the fat (hydrogenation) is obvious from the point of view of the raw materials that are available. Apart from coconut oil, palm kernel oil and cocoa butter, all oils marketed in Europe are liquid and are therefore unsuitable as semi-solid greases for applications such as spreading bread or bakery products .
When the oil is hydrogenated, hydrogen binds to the double bond of unsaturated fatty acids, in the presence of catalysts (usually nickel) that accelerate the reaction. The electrophilic addition of hydrogen is confined only to unsaturated fatty acids and does not involve the trivalent fatty ester (glycerol). The hydrogenation of the oil is influenced by time, temperature, hydrogen pressure, transport volume, catalyst (type, condition, concentration), the type of substrate 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 when fats deteriorate (rancidity), but the process can be artificially induced by the air bubbles found in the heated oil. The resulting peroxide compounds cause a greater reaction of the fatty acids and become polymers. These numerous and branched molecules give the oil a high viscosity, which allows them to stop at any stage adjusting blow times. Blown oils are used as lubricants because they adhere well to metals.
The esterification process alters the characteristics of fats and oils by redistributing the fatty acids in the glycerol organization. During the esterification process, fats and oils are divided into their components in a short time, before they are sorted and re-united to produce fats / oils for specific purposes.
Some examples of this include special bakery fats derived from palm kernel oil and coconut oil. The esterification reactions are very slow. For this reason strong catalysts, such as sodium, sodium hydroxide and sodium alcoholate, are added. Due to the large amount of various fatty acids present in fats and natural oils, there are innumerable possible combinations, so fats and oils that have certain classes are used
of glycerides in particular (for example, oils with C8-C14 chain).