Malaysian Palm Oil : The Introduction
All crude oils and fats are used for edible purposes including palm oil contain impurities. These impurities, such as free fatty acid (FFA), phosphatide, colouring matter, various flavor bodies, water, dirt particles, traces of metals, etc. must be removed prior to ending up with a bland, stable and right appearance product fit for consumption.
The refining processes in Malaysia include:
1. Alkaline Refining Process
Alkaline refining process basically consists of four main steps, namely:
- Earth Bleaching
Crude palm oil as we mentioned earlier contains some phospholipids which will affect the shelf life of the finished oil if not properly removed. So the first stage of refining is to treat the crude oil with 0.1% of phosphoric acid or citric in order to remove the phosphatides and some heavy metals prior to neutralization. The degumming action is mixing acid with the oil then a centrifugal mixer.
In this process, the degummed oil is mixed with 20-25 be caustic soda solution to remove the FFA. The lye concentration is proportional to the FFA content and the dosage volume is usually 20% excess in terms of the oil. The lye also is admixed to the oil centrifugal mixer and after a short time in contact, the oil ios sent through a high speed separator to separate out the soapstock, phosphatides and other sediments from the neutral oil.
1.3 Earth Bleaching and filtration
Bleaching is done under vacuum either in batch or continuous palnt with bleaching earth to reduce the content of the colouring substance in the oil and simultaneously it absorbs phosphatides, soap and heavy metals and decomposes the oxidation product such as peroxides. Dosage of bleaching earth ranges from 1%-2% depending on the quality of crude oil, required finished product specification, type of bleaching earth and bleaching temperature. In Malaysia, bleaching is carried out under 15-20mm HG vacuum at 90°c-130°c with contact from 20-40 minutes. After bleaching, the earth along with the colouring substances and others absorbed by the earth are removed from the oil by filtration through filter presses, and clear light neutralized bleached palm oil obtained.
Deodorization is the final major stage in the refining of edible oils to produce odourless and tasteless oil by removing the relatively volatile odoriferous and flavoured substances eg. FFA (under 0.10%), aldehydes, ketone, colour (below 3R 5 ¼” cell) etc. Deodorization is a process of steam distillation under vacuum (2-5 torr), involving deaeration and heating (230°c-250°c). To protect the oil against oxidation at all stages, air is removed prior to high temperature heating. The oil is cooled down to 55°c before pumped through a polishing filter. The end product is known as refined, bleached and deodorized (RBD) palm oil which is suitable for edible purpose.
2. Physical (Steam) Refining Process
Physical refining of crude palm oil is more common process in Malaysia because of its simplicity, higher efficiency, lower operation losses and lesser effluent problem. The main distinction is that the deacidification and deodorization prosses are accomplished in one specially designed stainless steel deodorizer whereas in the alkaline refining process, the deacidification is done by alkaline neutralizing. The whole process for physical refining can be divided into two sections:-
2.1 Pre-treatment and bleaching process
Crude palm oil is pre-treated with a suitable quantity of phosphoric acid to remove the phosphadites, trace metals, etc. The acid treated oil is then bleached with activated earth.
2.2 Deacaidification and deodorization process
The pre-treated oil is first heated up to 240°c-260°c under 2-6mm Hg and the FFA in the crude palm oil is then stripped off by live steam to about o.o5% level. The FFZ together with entrained oil is collected as a fatty acid distillate and it contains about 80-95% of fatty acid. The oil is further distilled by steam to remove all odoriferous constituents, peroxide and other volatile impurities. The oil is cooled down to 55°c prior to polishing. The final products obtained have the same specification as that produced by the alkaline refining process.
Natural oils and fats have different characteristics due to the fact that they are composed of a great number of different triglycerides. These contain fatty acids with carbon chains of different lengths and with different degrees of unsaturation.
Triglycerides with a high degree of unsaturation as indicated by a high iodine value, have a lower melting point than those containing more saturated fatty acids. If an oil is cooled to a certain temperature, the high melting triglyceride (stearin) will crystalise while the low-melting ones will remain fluid. The stearin can then be separated from oil (olein) by different methods and the fat/oil is thus divided into two fractions: Stearin with a high melting point and olein with a low cloud and melting point.
This technique is called fractional crystallization and is used to obtain oils or fats more suitable for example, as cooking oils or for margarine/shortening production.
Palm oil by virtue of its composition renders itself for franctionation either from crude palm oil or processed palm oil into olein and stearin fractions. Two-stage fractionation of palm oil has been carried out experimentally on a planet scale.
Three palm oil fractionation processes which are used by refiners in Malaysia are:
3.1 Dry fractionation: through batch crystallization of the oil without using additives by controlled cooling and subsequent continuous filtration.
3.2 Detergent fractionation: through batch or continuous crystallization of the oil by controlled cooling and separation of the fractions by centrifugation after adding a surfactant.
3.3 Solvent fractionation: through continuous crystallization of the oil in a solvent followed by separation of the liquid and solid fractions through a continuous drum filter.