ABSTRACT
Crystallization refers to the formation of a solid from a liquid. During crystallization, randomly oriented molecules of the liquid undergo phase transition to form a solid characterized by a crystalline lattice of highly organized molecules or atoms. The crystallization process consists of four steps: (1) achievement of a thermodynamic driving force for crystallization, (2) nucleation, (3) crystal growth, and (4) recrystallization [1]. The rst requirement to form a crystal is the generation of a sufcient thermodynamic driving force for crystallization. Once a sufcient driving force is reached, nuclei will form and, given enough time, these nuclei will grow to form a crystal. Finally, over time, crystals reorganize and recrystallize to reach the most favorable energy state and form a stable crystalline network characterized by specic physical properties. The crystallization process can be affected by several process conditions that affect any of the four steps mentioned earlier. Process conditions of interest include but are not limited to crystallization temperature, agitation, and cooling rate. This chapter will describe the fundamentals of lipid crystallization and will
I. Crystallization: General Principles ...................................................................................... 327 A. Thermodynamic Driving Force ................................................................................... 328
1. Crystallization in Solutions .................................................................................... 328 2. Crystallization from the Melt ................................................................................. 329
B. Nucleation ..................................................................................................................... 329 C. Crystal Growth and Recrystallization .......................................................................... 331
II. Crystallization and Physical Properties of Fats .................................................................... 331 A. Lipid Classication ....................................................................................................... 331 B. Triacylglycerol Crystal Packing Structure: Polymorphism .......................................... 333 C. Phase Behavior ............................................................................................................. 335 D. Solid Fat Content .......................................................................................................... 337 E. Melting Behavior .......................................................................................................... 337 F. Crystal Morphology ..................................................................................................... 338 G. Texture and Viscoelasticity .......................................................................................... 338
III. Effect of Processing Conditions on Crystallization Behavior of Fats .................................. 338 A. Crystallization Temperature ......................................................................................... 338 B. Cooling Rate .................................................................................................................340 C. Agitation ....................................................................................................................... 341 D. Use of Additives ........................................................................................................... 342 E. Other Processing Conditions ........................................................................................ 342
1. High-Intensity Ultrasound ...................................................................................... 342 2. High-Pressure Crystallization ................................................................................344
