Bulk fats

Proton NMR spectroscopy ( H MRS) has shown to offer excellent possibilities for evaluation of biochemistry in vivo. Due to its non-invasive character it is of increasing interest not only for the study of human brain diseases, which describe the majority of clinical applications, but also for metabolic characterization of organs outside the brain, as prostate, liver, heart or skeletal muscle. Studies on skeletal muscle have been of increasing interest during the last years, since it was shown that MRS enables the differentiation between two muscular lipid compartments the bulk fat components along the fasciae and muscular boundaries, which are called extramyocellular lipids (EMCL), and the metabolically highly active intramyocellular lipids (IMCL). The latter are stored in spherical droplets in the cytoplasm of muscle... 

Figure 1 Melting enthalpy of bulk fat and emulsified fat of ice cream mix with (+E) and without (-E) emulsifier after cooling at 5°C measured by DSC.

Heat dissipation in bulk fat is considerably slower than in milk or cream this is related to the lower thermal conductivity of bulk fat and, in particular, the fact that bulk fat cannot be agitated efficiently. 

The composition of bulk fat is uniform, but differences from globule to globule are known to occur (see Section 5.3) consequently, considerable differences may occur in the final melting point of the fat between different globules. 

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... 

Differences in nucleation explain the differences observed between crystallization in the bulk and emulsified states. In bulk fats, only a small number of nuclei are needed to induce crystallization. However, when the same fat is emulsified, each fat droplet must contain a nucleus or impurity in order to crystallize, the probability of which is low. As a result, the emulsified fat requires more supercooling (i.e., to a lower temperature) in order to nucleate (Walstra et al., 1994). 

Bulk fat products are considered to be plastic materials that are elastic when the stress and strain are below the yield stress and are viscous above the yield stress. The elastic properties of the fat are modeled using Equation (17.16) and the viscous component is modeled using Equation (17.17),... 

It is widely recognized that the size of the emulsion droplets is an important factor in the extent of subcooling (11). Smaller droplet size leads to nucleation at a lower temperature (greater degree of subcooling). Thus, the probability of nucleation within an emulsion droplet is lower than in the bulk fat (38). The dispersity of droplet sizes, however, did not change the critical subcooling required for onset of nucleation (39). 

Scale of Operation The size of the batch being crystallized may influence rate of crystallization. For example, crystallization from an emulsion generally occurs at a lower temperature than for the bulk fat based on the separation of catalyzing nucleation sites. In an emulsion, the catalyzing nucleation sites are more dispersed (spread through the number of droplets) and this leads to nucleation at a lower temperature than the same fat in bulk phase. 

AMF) as a bulk fat system and milkfat globule of cream as an emulsion system (102-106). 

The same techniques developed for bulk fats can be equally employed to measure the crystallization of emulsified oils. In these cases, the experiments tend to be easier as the contraction of the fat on freezing does not lead to the formation of air spaces in the sample, but, on the other hand, because a smaller volume of material is undergoing a phase transition, the magnitude of the signal change, and thus the precision, is lower. 

Relating Bulk-Fat Properties to Emulsified Systems Characterization of Emulsion Destabilization by Crystallizing Fats... 

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. 

Exposure to a shear fleld causes more rapid crystallization as the presence of protruding crystals leads to more aggregation of crystalline droplets, similar to bulk-fat behavior. The rapid increase in the rate of droplet destabilization following crystal growth and protrusion is due to the shear induced by the less spherical... 

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