Crystal structure, fats transition

Figure 6. Polymorphic forms of fat crystals, including the possible polymorphic transitions, subcell packing structures, stability characteristic, and triacylglycerol stacking conformations.

Polymorphism. The structural stabihty of margarine is influenced by the properties of the crystal lattice and by the actual amount of solid fat present. Many organic compounds or mixtures such as fats can sohdify in more than one crystalline pattern. The primary crystal forms of triglycerides are designated a, p, and p, which correspond to three principal cross-sectional arrangements of the fatty acid chains (71). These may be differentiated by characteristic x-ray diffraction patterns (72) and heats of transition observed in calorimetric studies (73). Phase behavior of... 

In products containing lipids, control of the crystal polymorphic form is also necessary. Lipids form different crystalline structures, or polymorphs, depending on the nature of the fat and the processing conditions. Transitions from less stable to more stable polymorphs are also dependent on composition and processing conditions. For example, tempering (or precrystallization) of chocolate is a process through which the chocolate is sequentially cooled and warmed to promote crystallization of cocoa butter into the desired polymorphic form. Controlling crystallization to produce the proper size distribution of this polymorph provides ... 

The incorporation of lecithin in different amounts (10-50% related to the triglyceride) did not influence the melting or crystallization temperature of the hard fat in the bulk phase neither in the nanoparticles but led to an accelerated polymorphic transition to the stable 6-modification particularly in the nanoparticles. No additional colloidal structures derived from the emulsifiers (lecithin and Solutol) could be detected in the aqueous phase by electron microscopy and the results of H- and P-NMR studies indicate that lecithin and Solutol are nearly completely attached to the particle surface. However, from the results it was also concluded that due to the redistribution of the lecithin from the lipid matrix and its enrichment in the particle interface, neither an increase in drug load (into the solid... 

Emulsifiers sensitively modify the rates of crystal growth and polymorphic transition of fats through the preferred adsorption at or inclusion in fat crystals [55,56]. The retardation or acceleration of the polymorphic transformation is influenced by the hydrophobic moiety structure. Figure 20 shows the effect of emulsifiers on the a-to-p transformation of tristearin during aging at room temperature... 

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