Palm oil crystallization

The crystallization behavior of milk fat (which contains minor lipids) and a pure triacylglycerol fraction of milk fat were compared by Herrera et al. (1999). The results suggested that minor lipids delay nucleation but promote crystal growth. Other workers who examined the effects of added phospholipids on palm oil, suggested that some phospholipids delayed nucleation while others had more significant effects on the rate of growth of fat crystals (Smith, 2000),... 

Chong, C.L. 2001. Crystallization of palm oil products. In, Crystallization and Solidification Properties of Lipids (N. Widlak, R. Hartel, S. Narine, eds.), pp. 110-119, AOCS Press, Champaign, IL. 

Litwinenko, J.W., Rojas, A.M., Gerschenson L.N., and Marangoni A.G. (2002). Relationship between crystallization behavior, microstmeture, and mechanical properties in a palm oil based shortening. Journal of American Oil Chemists Society. 79,647A154. 

Kloek, W., Walstra, P. and Van Vliet, T. (2000). Crystallization kinetics of fully hydrogenated palm oil in sunflower oil mixtures. Journal of American Oil Chemists Society, 77(4) 389-398. 

During processing of fats, crystallization is often used to modify the properties of the fat. For example, winterization of vegetable oils is needed to ensure that the oil remains a clear liquid even when stored at low temperatures for extended time periods. The process of fractionation of fats to produce components of natural fats with different melting properties also requires control of crystallization to optimize the separation process. Many fats, including palm oil, palm-kernel oil, milk fat, and tallow, are fractionated by crystallization to produce different functional fats. 

In this section, the polymorphic properties of natural fats are briefly discussed by highlighting miMat, cocoa butter, and palm oil fraction based on recent research into the effects of external factors on the polymorphic crystallization such as shear stress, ultrasound stimulation, and addition of food emulsifiers. 

Figure 27. Optical micrographs of isothermal crystallization of palm oil with and without an additive (1 wt.% of polyglycerine behenic acid ester). (A) 60 min at 2CPC without the additive (B) 60 min at 20f C with the additive (C) 60 min at 2T C without additive (D) 60 min at 27°C with the additive. (This figure is available in full color at http //www.mnv.interscience.wiley.com/biofp.)...

Dry fractionation is a two-step operation involving crystallization that should be allowed to proceed slowly to the equilibrium state, followed by hltration of the solid from the liquid phase. Crystallization occurs over several hours and requires good temperature control. The temperature must be lowered at a hxed rate to the selected value, and this must be combined with efficient but slow agitation. Good filtration—aiming at complete separation of solid and liquid—is important and may be carried out under reduced pressure using a Florentine hlter or under pressures up to 5 Mpa (50 bar) with a membrane hlter. Fractionation is applied mainly to palm oil but also to lauric oils (coconut and palmkemel), butter oil, beef tallow, hardened soybean, and cottonseed oil. 

This renewed popularity was most likely at the expense of tallow and palm oil, which lost consumer appeal due to unfavorable publicity highhghting nutritional concerns with saturated fatty acids or cholesterol both of these edible fats and oils crystallize in the beta-prime habit like cottonseed oil. 

Knowledge about the detailed structures of the triglycerides present in palm oil is important because they define some of the physical characteristics of the oil. The melting points of triglycerides are dependent on the structures and position of the component acids present. They also affect the crystallization behavior of the oil. The semisolid nature of palm oil at room temperature has been attributed to the presence of the oleo-disaturated fraction. 

As mentioned previously, partial glycerides are artifacts of the extraction process, especially the stages prior to sterilization. Oil obtained from unbruised sterilized fruits shows trace levels of partial glycerides. Random analyses of samples of refined palm oil, pahn olein, and palm stearin have shown the presence of about 2% of 1,2-diglycerides and about 4% of 1,3-diglycerides with trace amounts of monoglycerides. These partial glycerides are important as they are known to affect the crystallization behavior of the oil. 

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