Polymorphism in fats and oils

Kiyotaka Sato Graduate School of Biosphere Science, Hiroshima University, Higashi-Hrroshrma, Japan, Polymorphism in 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. 

Commercial fats solidify in several crystalline polymorphic forms. Two desirable stable forms are commonly designated by the Greek letters beta ((3) and beta-prime (p )- Table 2 (7) lists many common fats and oils and their most commonly exhibited polymorphic crystalline form. 

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). 

Fats and oils constitute a very large portion of the food industry. Fats are multicomponent systems containing many different triglycerides (and other lipids in smaller amounts). They crystallize in different polymorphic forms, often termed a, P and P in order of thermodynamic stability and melting point. The proportions of these phases in final products largely determine basic quality attributes of the material, such as palatability, appearance or shelf life. 

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