Fats and oils are fractionated to enhance their performance and / or increase their commercial value, or even to make special products.
Fractionation can be applied to crude, deacidified and bleached oils or to
oils that have only been bleached.
Fats and oils are not homogeneous substances, but mixtures of several triglycerides with different melting points. This affects their physical characteristics. Thus, fats and oils do not have a defined melting point but a melting range. This feature is used for separation purposes.
Fractionation is a purely physical process, in which the components of fat and triglycerides remain unchanged. The separation is determined exclusively by the melting point or, in the case of wet fractionation, by the solubility in a suitable solvent. The liquid components of a fat are present as
droplets in a crystalline lattice of components with higher melting points that emerge with difficulty outwards. Despite the use of modern equipment, the process lasts several hours and can be divided into the following stages:
– Fusion or dissolution of fat / oil
– Conditioning
– Crystallization
– Separation
The three methods currently used for fractionation are:
1. Dry fractionation (without adjuvants)
The dry fractionation is based on the principle of separation according to the different melting points on several components, for example olein and stearin. The process has the advantage of being purely physical, and does not imply adding additives of any kind and, thus, dispensing it from the need to purify the resulting product. One disadvantage is the relatively poor separation, compared to the other processes. The dry fractionation is carried out by heating the mixture to a temperature above the melting point and then letting it stand so that it cools and separates, generally in two fractions.
2. Lance Fractionation
The principle is based on a patent granted to the Lanza brothers in 1905. The separation is not done mechanically, but the crystalline surface is moistened with aqueous detergents, in which salts can also be mixed. This hinders emulsification. The humidity produces that the components with high melting points of the oil become hydrophilic and pass to an aqueous phase. This produces numerous droplets of free-crystalline oil that then bind. In the next step of the process, the two phases are separated by centrifugation.
3. Wet fractionation
The principle is based on differences in the solubility of the solvent at a given temperature. This causes an acute separation of the different phases, which can be controlled by adjusting the temperature and the amount of solvent. If very pure fractions are required, the product can be re-washed with a solvent and remove the latter.
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.