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DRY FRACTIONATION OF LIPIDS


Dry fractionation of oils and fats is the separation of high-melting triglycerides from low-melting triglycerides by crystallisation from the melt. Apart from blending, it is the cheapest process in oils and fats processing. It is a pure physical process compared to other chemical modification processes such as hydrogenation and interesterification which modify triglycerides. Dry fractionation has probably been used for the first time in 1872, when Mège Mouriès produced the first margarine. Dry fractionation is now applied to many kinds of fats: palm oil, anhydrous milk fat, tallow, fish oil, lard, cottonseed oil, sunflower seed oil, palm kernel oil, tallow butter fats, and special fats.

The most important applications are: palm olein used extensively as frying oil, palm super olein as salad oil and frying oil, the palm-mid fraction as component of cocoa butter equivalent, palm kernel stearin as cocoa butter substitute, anhydrous milk fat fractions for bakery and confectionery products, spreadable butter, tallow olein for frying oil and spreads. In this process, the fat is melted and heated to eliminate any crystal memory. The molten fat is cooled down under controlled agitation and cooling conditions to produce crystals nuclei formed by the higher melting triglycerides. Then, nuclei will grow to form crystals of the desired size. When the crystallisation has progressed far enough, the slurry is separated.

Apparently, it looks simple, but in practice, this physical process is complicated by the fact that the formation of nuclei depends on the foreign particles, the agitation, the temperature, the triglycerides composition and the type of pre-treatment followed by the fat. A review of the whole process was released by Timms RE (Eur J Lipid Sci Technol 2005, 107, 48).
Since the initial description of the process patented in 1968 (
Tirtiaux F : Procédé et installation de cristallisation par refroidissement. Belgian Patent 713430, 1968), several reports were released on dry fractionation of various types of lipids.

Taking into account the absence of solvents and trans-fatty acid production, it was predicted that the dominant modification process of the 21st century will be fractional crystallisation, just as it was at the beginning of the modern oils- and fats-processing industry after Mège-Mouriès invented margarine (Timms RE, Eur J Lipid Sci Technol 2005, 107, 48).


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