High Pressure Processing Effects on Lipids Thermophysical Properties and Crystallization Kinetics

This review examines the combined pressure-thermal effects on thermophysical and crystallization properties of lipids. Pressure treatment transiently accelerates the phase transition and shifts the melting temperature of lipids by 10 A degrees C/100 MPa-20 A degrees C/100 MPa. It also transiently alters various thermophysical properties of lipids including density, viscosity, thermal conductivity, and specific heat. The interdependence phase transition of lipids with their corresponding thermophysical properties is highlighted. The magnitude and rate of pressure application influences the mechanism of lipid crystallization under pressure. For example, slow multi-step modest pressure buildup (100-200 MPa) promotes heterogeneous nucleation and slow crystallization which result in stable crystal structures. Increasing the magnitude of pressure by 400-500 MPa accelerates the nucleation rate significantly. On the other hand, rapid single-step pressurization, regardless of pressure level, induces instantaneous volumetric crystallization of less stable crystal structure which is subsequently modified into stable crystal polymorphs during depressurization. High pressure crystallization is also influenced by temperature, pressure holding time, compression rate, compression cycle, and lipid compositions. The effects of pressure treatment are more pronounced in saturated fatty acids compared to unsaturated ones, and it is shown that triglycerides crystallize more slowly under pressure than free fatty acids.