Bulk fats polymorphism

The dispersed state has a considerable effect on fat crystal polymorphism. Lopez et al. (2000, 2001c) observed that crystallization in milk fat globules is more disordered than in bulk fat. On slow cooling, milk fat crystallizes in the a form in cream (Lopez et al., 2001a), whereas in anhydrous milk fat, it crystallizes first in the (3 form and then in the a form (Lopez et al., 2001b). Rapid cooling of cream or anhydrous milk fat from 60 to 4°C leads to the formation of a crystalline structures, which transformed into (3 structures... 

Fat crystallization has been extensively studied in bulk fats and, to a lesser extent, in emulsified fats. It has been shown that the crystallization behavior of a fat will proceed quite differently, depending on whether it is in bulk or emulsified form (4,5). Authors have examined the effect of the state of dispersion on the crystallization mechanisms (nucleation, crystallization rate) and polymorphic behavior (6-11) of partial- and triglycerides in bulk and emulsified form. Understanding the mechanisms of emulsion nucleation and crystallization is one of the first steps in understanding the destabilization of emulsions and partial coalescence, e.g., stabilization of liquid fat emulsions by solid particles (fat) or control of the polymorphic form of crystals during the process of partial coalescence to control the size of aggregates and textural properties. 

Crystallization from the emulsified state may lead to different nucleation processes than observed for the same fat in bulk liquid form. It has been suggested that nucleation often occurs at the interface of the droplet where surface-active agents are located. The general similarity of the lipophilic components of surfactants oriented at the surface may provide some ordering and structure for the lipid molecules within the droplet and enhance nucleation, as found for example by Kaneko et al. (40) for a hydrocarbon emulsion. Walstra (11) also suggests that formation of compound crystals from emulsions of natural fats may be different than the same fat crystallized from bulk liquid. The initial polymorph formed may also be different, with more stable polymorphs more likely to form in the emulsion (38). 

Crystallization of lard and PSCO emulsions with similar initial droplet size distributions led to partial coalescence under perikinetic and orthokinetic conditions. The application of shear accelerated the destabilization of the emulsions after the achievement of a critical SFC. The SFC was found not to be the sole contributing factor to emulsion destabilization. Crystal morphology and distribution within the droplet are important factors in the destabilization of these emulsified fats. The emulsions are relatively stable in the short term when crystals are small and form quickly in a consolidated mass in the bulk of the droplet. Polymorphic transitions were not detectable as a source of destabilization in this experiment. The observation of the microstructure of bulk and emulsified fats gave insight into the mechanisms of emulsion destabilization. 

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 are key players in polymorphic transformation studies. They alter the fat surface properties, resulting in changes in crystal size and nature. Early reviews by van den Tempel [52] and Garti [53] showed that many types of emulsifiers tend to reduce the crystal growth rate of natural fat blends. Since then, further work has been performed on the effects of different emulsifiers on fats not only in bulk but also in emulsion systems. Garti and Yano [54] discuss in great detail the progress made in this field in recent years. 

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