Fractionation

The triglyceride composition of palm oil is such that its major triglycerides include oleodipalmitin with a melting point of 37°C and palmitodiolein with a melting point of 19°C.

The aim of fractionation is to produce a liquid olein (slip melting point 21.6°C and cloud point 8.8°C) and a solid stearin. The olein is used mainly as a liquid vegetable oil for cooking and frying, while the stearin fraction is used in margarine, shortening, and frying fat.

In Malaysia, fractionation of palm oil into the low melting point olein and the high melting point stearin is done by two processes, referred to as dry fractionation and detergent fractionation.

During dry fractionation, the oil is first heated to 70-75°C to melt all crystal nuclei. The heated oil is then passed to a crystallizer equipped with a cooling jacket where it is cooled to 18-20°C for 4-8 h. The crystallization of stearin in liquid olein causes slurry formation. The liquid olein is separated from the solid stearin by membrane filtration of the slurry.

In detergent fractionation, the separation of olein and stearin is made possible by mixing the crystalline slurry with a detergent solution (sodium lauryl sulfate and magnesium sulfate). On centrifuging, the lighter olein is separated from the heavier aqueous phase containing the stearin. The liquid olein is washed, dried, and sent for storage while the stearin is recovered from the aqueous phase and the detergent is recycled. Special doubly fractionated olein (superolein) with a lower cloud point and higher iodine value and a softer stearin known as palm midfrac-tion (PMF) can be obtained by a second fractionation. Crude palm oil can also undergo detergent fractionation, first to produce crude olein and crude stearin and thereafter refined to obtain the edible grades of palm olein and palm stearin.

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