Crystallization, fats crystal polymorph

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... 

The sensory properties, especially texture and appearance, of milk fat-based products such as butter, cream, cheese, ice cream and milk chocolate are largely dependent on the physical properties of the product, especially properties governed by the phase change behavior of the fat, used here to mean melting and crystallisation behavior, crystal polymorphism and microstructure (Birker and Padley, 1987 O Brien, 2003). The same may be said of the functional properties of milk fat, milk fat fractions and milk fat-based products when these are used as food ingredients. 

In the context of milk fat, DSC is most widely used to measure temperatures and heats of transitions (phase changes). It is also used to measure specific heat, solid fat content, crystallization kinetics constants and fat purity, and in the study of fat crystal polymorphism. 

Oils and fats go through a series of increasingly organized crystal phases upon cooling. This multiple form of crystallization (polymorphism) is an important characteristic of fats and oils because it greatly influences the textural and functional properties of fats and fat-based products. 

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 ... 

Crystal polymorphic form strongly influences final dough properties. For example, according to Knightly [143] and Baldwin et al. [142], the P form is best for fats used in bread and cakes whereas the P form is best for pie crusts. Where air incorporation is important, p crystals in dough provide for many small bubbles and greater loaf volume whereas P crystals allow the incorporation of... 

D. Adsorption on Fats and Polymorphism-Crystal Structure Modification... 

Crystal polymorph plays a key role in final product consistency and acceptability. Smaller crystals lead to firmer fat products, whereas larger fats give a sense of sandiness in the mouth. Incorporation of large amounts of liquid oil increases the tendency of the desirable P polymorphic form to convert to the p form (deMan et al., 1995). In the production of butterfat-canola oil spreads, preserving the P form would be essential in order to avoid a sandy mouthfeel. 

Beta crystals are considered the most stable crystal polymorph (Lutton, 1950). In the examined samples, as the proportion of oil increased, so did the presence of p crystals. Microstructurally, aggregation in the form of spherulites became more pronounced. Aggregation behavior was more apparent in the CIE samples than in the NIE samples. CIEIOO was almost devoid of p crystals, yet it demonstrated substantial aggregation. Thus, aggregation in fat crystals cannot be readily explained by polymorphic form. Other factors such as the rheological properties of the spreads must have come into play. 

As shown by deMan and deMan (1994) and others (Desmedt et al., 1990 Gray et al., 1976), the more a fat is diluted with liquid oil, the more likely it is that P-crystal polymorphs will form. This was generally the case in both fat systems. 

Tempering. The state, or physical stmcture, of the fat base in which sugar, cocoa, and milk soHds are suspended is critical to the overall quaHty and stabiHty of chocolate. Production of a stable fat base is compHcated because the cocoa butter in soHdified chocolate exists in several polymorphic forms. Tempering is the process of inducing satisfactory crystal nucleation of the Hquid fat in chocolate. 

Crystallization and Polymorphism of Fats and Fatty Acids, edited by Nissim Garti and Kiyotaka Sato... 

Microemulsions and Related Systems Formulation, Solvency, and Physical Properties, edited by Maurice Bourrel and Robert S. Schechter Crystallization and Polymorphism of Fats and Fatty Acids, edited by Nissim Garti and Kiyotaka Sato... 

Kaneko E, Polymorphism and phase transitions of fatty acids and acylglycerols, in Crystallization Processes in Fats and Lipid Systems, Garti N. and Sato K., eds., Marcel Dekker, New York, 2001, 53-97. 

Cocoa butter NF is defined as the fat obtained from the seed of Theobroma Cacao Linne (Family Sterculiaceae) (44). Cocoa butter softens at 30°C and melts at 34°C. It contains four different forms alpha, beta, beta prime, and gamma with melting points of 22°C, 34°C to 35°C, 28°C and 18°C, respectively. The beta form is the most stable and is desired for suppositories. The biggest challenge with the polymorphism of cocoa butter is the impact of the manufacturing process on the characteristics of the suppository itself. When cocoa butter is hastily melted at a temperature greatly exceeding the minimum required temperature and then quickly chilled, the result is metastable crystalline form (a crystals), which may not even... 

In many instances, TGs exist in polymorphic forms. Crystal structure is very important to the properties of margarines, shortenings, and specialty fats. The very unstable a form is readily transformed to the more stable ft form, which in some TGs has a higher melting point (more stable) than the /3 form. In single-acid TGs, the order is a — f3 — a, but some mixed TGs show a lower-melting (less stable) (3 form. This is further complicated by the existence of multiple / and /3 forms, depending upon the detailed TG structures at hand. 

Localized NMR spectroscopy, which is often called as MRS in comparison with MRI, is not so familiar technique in food science, because a specific pulse sequence such as ISIS and a facility which can precisely follow the pulse sequence without any contamination from other position is needed for localization of position. The localized NMR is usually used together with NMR imaging. The study of solid/liquid ratios, fat structure and polymorphism and the kinetics of fat crystallization was reviewed [24], The potential of applications in food process development and control was offered. The localized spectra of sausages in areas of 0.3 mm X 0.05 mm (thickness of sample =1.5 mm) were obtained by the spin echo 2DFT method [113], in which the difference in the tissue structure was discussed with relation to the process and original materials. McCarthy et al. determined mobility of water in foams by using a localized spectroscopy [114]. T2 relaxation time varies in the foam as function of diameter and its variation was analyzed by the classic 2-state fast exchange model. 

The (3 polymorph is the most thermodynamically stable. It has the highest melting point and is therefore the least soluble in a melt at a given temperature below its melting point. Despite this, nucleation for the a-polymorph is favored. Although the a-crystal is less stable, it has a lower crystal-melt interfacial tension and lower heat of crystallization than the (3 - and (3-polymorphs (Timms, 1995). Nucleation in milk fat typically... 

Although the a-polymorph is meta-stable, it can have a relatively long lifetime in milk fat at low temperatures compared to other fats (Walstra et al., 1994). The a-crystal may be stabilized by the formation of compound crystals in milk fat (Walstra et al., 1999). A consequence of both polymorphism and mixed crystal formation in milk fat is that the material is rarely at equilibrium (Walstra et al., 1994). 

Boistelle, R. 1988. Fundamentals of nucleation and crystal growth. In Crystallization and Polymorphism of Fats and Fatty Acids (N. Garti, K. Sato, eds.), pp. 189-226, Marcel Dekker Inc., New York. 

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