Brief Overview
Refined Bleached Deodorized (RBD) Palm stearin is a vegetable fat, derived from palm oil. RBD palm stearin is a solid fraction of RBD palm oil, obtained by fractionation using simple crystallization and separation processes at a controlled temperature. The physical properties of RBD palm stearin differ widely from those of RBD palm oil. RBD palm stearin is available on a broader range of melting points and iodine values.
RBD palm stearin is cholesterol-free and has an anti-blood-clotting effect, which helps prevent heart disease. RBD palm stearin contains vitamin E, vitamin D, and an approximately equal proportion of saturated and unsaturated fatty acids. RBD palm stearin is highly stable against oxidation due to the presence of tocopherols, which acts as a natural antioxidant and oxidized before the oxidation of RBD Palm stearin.
Manufacturing Process
RBD palm stearin is obtained by the fractionation of RBD palm oil. RBD palm oil contains a combination of fatty acids with different chain lengths and degrees of unsaturation. This results in a broad range of melting points of RBD palm oil. Crystallization of RBD palm oil under controlled cooling followed by separation yields a low melting liquid phase i.e. RBD palm olein and a high melting solid phase i.e. RBD palm stearin.
The followings are some factors that affect the rate of crystallization:
Oil Composition: RBD palm oil contains about 5-8% of diglyceride and approximately 1% monoglyceride. Diglyceride forms a eutectic mixture with triglyceride resulting in lower solid content. Monoglyceride and other minor components present in RBD palm oil don’t affect much the crystallization process.
Polymorphism: Triglycerides present in RBD palm oil are polymorphic in natural form and so they can crystallize in more than one form. Upon cooling, RBD palm oil crystallized to α-form crystal. Upon further cooling, it gradually transforms in the order of α to β’ to β forms. β’ form is the most stable crystal, so for good separation, it is desirable to have β’ form
Cooling rate: This process affects the nucleation and crystal growth of RBD palm oil. When the temperature is sufficiently low, saturated glycerides of RBD palm oil start forming crystals and these crystals act as nuclei for further crystallization of lower melting glyceride. This process results in the formation of a larger cluster of crystals.
There are three industrial processes for the fractionation of RBD palm oils: Dry, detergent, and solvent process.
Dry Fractionation: This is a fully physical process. It does not require the use of any chemicals or additives so there is no yield loss and no contamination. There are no chemical changes to RBD palm oil.
First, the RBD oil is heated to approximately 70ºC and homogenized to fully melt the glycerides, and then hot and homogenized oil is allowed to cool in a controlled manner. Chilled water is circulated for cooling purposes. When the oil temperature reaches the desired cooling temperature, which depends upon the quality of RBD palm oil, the cooling process is stopped. The thick crystallized mass is filtered using a drum rotary filter and membrane filter to liquid RBD palm olein and solid RBD palm stearin.
Detergent Fractionation: This process is mainly used for the fractionation of crude palm oil. In this process, The RBD palm oil is first cooled in a crystallizer with chilled water to allow the crystallization of higher melting glycerides. When it reaches to desired cooling temperature, the crystallized mass is mixed with an aqueous detergent solution containing 0.05% sodium lauryl sulfate and magnesium sulfate. The crystallized mass is wetted with detergent and separated out in suspension in an aqueous solution. Now it is sent to the centrifugal separator where olein is discharged as a lighter phase and stearin remains as part of the aqueous phase
Solvent Fractionation: In this process, a solvent like hexane or acetone is used for the fractionation of RBD palm oil. This is the most expensive process due to the use of solvent and solvent recovery machinery cost. In this process, RBD palm oil is first mixed with a solvent and followed by cooling to desired crystals. Now the mixture containing partially crystallized oil and the solvent is filtered using a vacuum filter
