Milkfat polymorphism

Van Beresteyn, E.C.EI. 1972. Polymorphism in milkfat in relation to the solid/liquid ratio. Neth. Milk Dairy J. 26, 117-130. 

Crystallization of milkfat is an important process for fractionation of its contents and production of butter, whipped cream, and ice cream. As the quality of these products strongly depends on polymorphism of milkfat, physical chemical properties of milkfat have been studied by many researchers (98). 

As for the polymorphism of milkfat, a and p forms frequently appear, and p form appears under special conditions when HMF and milkfat are stored for long duration (99-101). In regard to the effects of thermal treatment and emulsification on the polymorphic crystallization of milkfat, Lopez et al. recently performed synchrotron radiation X-ray diffraction and DSC studies, using anhydrous milkfat... 

Polymorphism and Milkfat High cooling rates (>l°C/min), or high levels of supercooling (>15°C), lead to the rapid formation of metastable a nuclei (34). The persistence of these unstable nuclei is dependent on thermal treatments that occur after crystallization. These nuclei may remain in the a form or convert... 

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. 

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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