Crystallization, fats latent heat

The congeal point, also called the setting point (O Brien, 2003), is a measure of the solidification point of a molten fat under the conditions of the test. The molten fat, contained in a beaker, is cooled until the cloud point is observed, and then cooled further until a certain subjectively assessed degree of turbidity (caused by the presence of fat crystals) is reached. The beaker is then kept at 20°C and the temperature of the sample recorded over time. The temperature rises initially owing to the release of latent heat of crystallization and then drops. The maximum temperature reached is recorded as the congeal point. 

The supercooled stream from the A unit flows directly to the worker unit. There is normally a 5-8°C (10-15°F) temperature rise across the B unit most of which results from latent heat of crystallization mechanical power does not add significantly to the total heat input. The plasticized fat from the B unit is forced through a special extrusion valve that also maintains an internal pressure of 17-20 bar... 

Tewkesbury et al. [42] studied the cooling of chocolate from the molten state. The single event that occurs during this step is the crystallization of the fat phase, often mainly cocoa butter. They used commercially available software, FIDAP, to compute the simulations. With it, they solved the heat conservation equation with a finite element method and made a basic assumption for crystallization The release of latent heat is assumed to be linear in the melting range of the cocoa butter, chosen to be between 21°C and 32°C. With this hypothesis, all parameters present in the equations are known for the liquid and solid phases ... 

Two approaches can be used to model crystallization kinetics of triglycerides and fat. If the microscopic parameters can be determined, the use of microscopic models is the most appropriate, because it applies directly the theory of nucleation and growth. For example, in the case of spherulitic crystallization, kinetic parameters can be determined experimentally. Solidification can then be modeled in a detailed way with a numerical or stochastic model for the nucleation and growth of crystals. The latter kind of microscopic model is very interesting because it also gives the stereological parameters of the microstructure. Probabilistic or numerical models are easier to use, but they provide only the evolution of the latent heat or the evolution of the solid fraction in the sample. 

When TAG molecules in liquid fat collide under conditions that will allow crystallization, two opposing forces come into play. One is the latent heat of crystallization, which has a positive effect as energy is evolved, reducing the entropy of the system. Second, for the crystal to grow and expand, energy is required to overcome the increasing surface tension. When the former exceeds the latter, a stable crystal nucleus is formed. 

The main solvents used for fractionation are acetone and hexane. However, only the Bernadini process [42] was designed around the use of the latter. Although it requires lower crystallization temperatures, hexane has a much lower latent heat of evaporation than acetone. The solvent-to-oil ratio required for hexane fractionation is lower than that for acetone because the solubility of fats in hexane is higher. However, its drawback is that hexane has a lower selectivity for triglycerides than acetone. In addition, hexane, unlike acetone, does not require rectification for drying after recovery. Thus the energy required for solvent recovery is about half of that required for acetone. 

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