Palm polymorphism

Nucleation from the melt has been studied for palm oil, composed of triglycerides of palmitic and oleic acids, and exhibiting at least three polymorphs (van Putte and Bakker 1987). Nucleation curves (induction time x vs temperature T) of palm oil and palm stearin show discontinuities at 297 and 306 °C respectively, indicating the onset of nucleation, and the demarcation of the occurrence of the polymorphs, as confirmed by isothermal Differential Scanning Calorimetry (DSC) studies (Ng I990a,b). 

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. 

The high content of diglycerides (about 6%) in palm oil and the p stabilizing effect of diglycerides probably do not have any significant influence on the polymorphic behavior of canola oil blends with palm oil levels as above. The diglyceride content in canola oil blends is only raised slightly by addition of palm oil in the above levels (46). 

In accordance with the above, it has been found that slightly hydrogenated palm oil delayed polymorphic transition from (3 to (3 considerably, compared to no palm oil addition (43). 

Timms (21) has heat of fusion to 17.7-22.3 kcal/kg for milkfat, 24-31 kcal/kg for fully hardened milkfat, 26-29 kcal/kg for cocoa butter in the p polymorph, 22.6 kcal/kg for refined, bleached, and deodorized (RBD) palm oil, 29.7 kcal/kg for RBD palm kernel oil, 26.0 kcal/kg for RBD coconut oil, 31.6 kcal/kg for fully hardened palm kernel oil, and 31.2 kcal/kg for fully hardened coconut oil. The heat of fusion is an empirical physical property dependent on the thermal history or tempering of the oil. 

Effects of Tempering on Polymorphic Forms of Palm Oil (PO) Anhydrous Milk-Fat (AMF) Shortenings During Storage... 

Table 3 shows the crystal polymorphic form and Avrami exponent observed for crude and refined palm oil and refined palm kernel oil at the isothermal ciystal-lization temperature indicated. An Avrami exponent of three was observed for all the temperatures for the three types of oil even though the crystal may be in different polymorphic form as in the case of crude and refined palm oils. 

Avrami Exponents and Polymorphic Forms of Crude and Refined Palm Oil and Refined Palm Kernel OiF... 

For the work reported here, the polymorphic forms of the crystals of all the palm oil products at the temperatures measured are either in the 3 or 3 form or a mixture of both. The 3 polymorphic crystal form is plate-like while the 3 crystal form is spherulitic with needle-like projections from the center of the crystal as can be seen from the electron microscope pictures published by van Putte and Bakker (12). Therefore it can be seen that for the P polymorph, although the final overall shape of the crystal assumes the shape of a sphere in three dimensions, the plates or leaves that form the crystal are thin. This shows that as far as the actual growing sites of the crystal are concerned, growth is in two and not in three dimensions. 

The transformation of crystals from the P to the P form takes place in the solids present in a fat. However, the rate of this transformation is greatly influenced by the amount of liquid oil in the fat. A suitable method to estimate the p stability of a fat is temperature cycling. An example is given in Table 9, where palm oil products were subjected to temperature cycling between 4 and 20°C. A cycle may take two or more days. The polymorphic forms can be measured at the end of each cycle. A product such as hydrogenated palm oil or palm olein will show no presence of P polymorphs after four cycles. Palm oil and palm stearin will... 

Polymorphic Forms of Some Palm Oil Products Temperature Cycled Between 4 and 20 C ... 

Polymorphic Behavior of Hydrogenated Palm Oils Diluted with Canola OiP... 

H-palm olein Liquid oil Polymorphic form Cycle... 

FIGURE 15.12 Rate of crystallization (in the P -polymorph) of 12% hardened palm oil in sunflower oil. (a) Dependence of the volume fraction of crystals various values of the initial supersaturation In / 0 (indicated near the curves), varied by varying temperature, (b) Recalculated linear growth rates Lc during the process as a function of supersaturation In / the hatched region contains all the curves for In /J0 = 2.25-3.50. (After results by W. Kloek. Ph.D. thesis, Wageningen University, 1998.)... 

Table 3.18 The fi polymorphic stability of liquid oils containing hydrogenated palm olein...

These are fats rich in symmetrical disaturated TAGs which behave like cocoa butter in all respects, and are able to mix in all proportions with cocoa butter. The desirable characteristics of cocoa butter are due to the SOS TAGs (S = saturated) which provide suitable melting point and solid fat content to give rapid melt in the mouth and cooling sensations. Palm mid-fraction (PMF), which has high contents of POP, is easily formulated with other SOS fats for chocolate products (Berger 1981). About 70%-80% PMF with 20%-30% shea or sal stearin, or 60%-65% PMF with 20%-30% shea or sal stearin and 15%-20% illipe are suitable for plain and for milk chocolate with 15% milkfat. Compatibility of cocoa butter (CB) and CBE is affected by addition of milkfat and its fractions into the product (Sabariah etal. 1998). Eutectic interactions between anhydrous milkfat (AMF), CBE and CB were noticeable due to different polymorphism encountered in these fats. 

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