Crystallization of fats and oils

Richard W. Hartel University of Wisconsin, Madison, Wisconsin, Crystallization of Fats and Oils. 

Fats and oils often show multiple melting points. As an example, tristearin has three melting points at 52°C, 64°C and 70°C, because fats and oils solidify in more than one crystal form this property is known as polymorphism. Crystallization of fats and oils occurrs in two stages of nucleation and growth. 

Some oil-soluble emulsifiers affect the crystallization process and development of polymorphic forms of fats (4-8). Sucrose fatty acid ester or sucrose polyesters (SPE) and lecithins are well-known food emulsifiers (9,10). The main characteristics of lecithins and SPE useful in food applications are their oil-in-water and water-in-oil emulsifying properties, that result in dispersion with condensed milk and coffee whitener, and prevention of blooming in candy products and chocolate (7,9-11). But there are very few reports about two effects of SPE on the crystallization of fats and oils, i.e., enhancement and inhibition (12,13). 

Metin S., Haitel R.W. Crystallization of fats and oils. In Bailey s Industrial Oil and Fat Products, 6th edn, (F. Shahidi, ed.), John Wiley Sons, Ltd, Chichester, (2005). 

Solubility Properties. Fats and oils are characterized by virtually complete lack of miscibility with water. However, they are miscible in all proportions with many nonpolar organic solvents. Tme solubiHty depends on the thermal properties of the solute and solvent and the relative attractive forces between like and unlike molecules. Ideal solubiHties can be calculated from thermal properties. Most real solutions of fats and oils in organic solvents show positive deviation from ideaHty, particularly at higher concentrations. Determination of solubiHties of components of fat and oil mixtures is critical when designing separations of mixtures by fractional crystallization. 

The physical state of fats and oils and their crystal structures are important for application of such products. In addition, formulation of products for special applications such as bakery, confectionary, frying, salad dressing, margarines, and spreads requires special characteristics that make the products suitable for such purposes. Thus, each source material will be important for its physical and chemical characteristics and hence suitability as a food component. 

TABLE 5. Classification of Fats and Oils According to Crystal Habit (79). 

The term morphology is used to denote the general relation of the physical behavior and performance of fats and oils to their crystal structure and the molecular configuration of their triglyceride components (7). 

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. 

Crystallization characteristics of fats and oils were described in the section on polymorphism. The size, abundance, and stability of crystals are important in food processing/food service ingredients and consumer products. Clear salad oils are preferred, and are made by selecting low-melting-point oils that are winterized by chilling to crystalline the highermelting triacylglycerols, which are then removed by filtration. 

Cocoa butter substitutes and equivalents differ greatly with respect to their method of manufacture, source of fats, and functionaHty they are produced by several physical and chemical processes (17,18). Cocoa butter substitutes are produced from lauric acid fats such as coconut, palm, and palm kernel oils by fractionation and hydrogenation from domestic fats such as soy, com, and cotton seed oils by selective hydrogenation or from palm kernel stearines by fractionation. Cocoa butter equivalents can be produced from palm kernel oil and other specialty fats such as shea and ilHpe by fractional crystallization from glycerol and selected fatty acids by direct chemical synthesis or from edible beef tallow by acetone crystallization. 

C27H45OH, crystallising in the form of acicular crystals and found in all animal fats and oils, in bile, blood, brain tissue, milk, yolk of egg, the medullated sheaths of nerve fibres, the liver, kidneys and adrenal glands. 

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