Pressure‐induced phase transitions in triacylglycerides

Abstract

The melting point of triacylglycerides (TAGs) under atmospheric pressure depends on both the fatty acid composition and crystalline structure of the polymorphic state, which are influenced by the temperature treatment history of the TAG. In this contribution, the additional effect of high hydrostatic pressure is described. Samples were placed in a temperature-controlled cell and pressurized up to 450 MPa. The phase transition was investigated either by perpendicular light scattering and transmission or with a polarized-light microscope. The high-pressure polarized-light microscope allows a precise determination of the melting point. The investigated TAGs showed a significant nonlinear increase of the melting point with pressure. Light scattering and transmission were used to observe the phase change in the high-pressure cell. Similar to supercooling in temperature-induced phase transition, we found a dramatic increase of the delay time in our pressure-induced solidification. Even the dependency of this induction time on the control parameter pressure was similar to that in temperature-driven crystallization. We propose that different crystalline structures may be obtained by superpressuring instead of supercooling.

Growth Rate of Pressure‐Induced Triolein Crystals

“…Melting curve and microscopic pictures of three different morphologies. In the diagram, stars and diamonds indicate the melting points of β‐ and β’‐crystals at atmospheric pressure (Belitz et al, ) and the melting curve (Ferstl et al, ). The letters denote pressure and temperature where the respective morphologies are observed, i.e., at a temperature of 283.16 K and at pressures of 115, 155, and 190 MPa, respectively.…”

“…Taken the material data for the sample and for the PMMA plates (Assael et al, ; Morad et al, ), one can estimate that the heat generated during the pressure ramp can be conducted in a few minutes. Former measurements in cuvettes where the sample temperature was measured directly have shown that isothermal conditions were reached about 10 min after pressurization (Ferstl et al, ). Hence, in particular the long crossover times of more than 100 min at rather low pressures cannot be explained by the retardation due to heat of compression.…”

“…Tefelski et al () studied solidified technical‐grade triolein at a pressure of 400 MPa with Raman spectroscopy and found a spectrum that corresponds to β‐crystals. Ferstl et al () determined the melting curve of triolein β‐crystals with a polarization microscope up to pressures of about 400 MPa. They also measured the induction time and showed that the growth rate of single triolein crystals is constant in time and does not vary between different experimental runs (Ferstl et al, ).…”

Promotional Effects of New Types of Additives on Fat Crystallization

“…However, the short-spacing peaks for the β form appeared at 27.6-25. 8 LLL talc and 24.2-23.1 LLL CNT during the cooling processes, as shown by the dotted arrows in Figs. 4b and c. The intensities of these peaks for the β form increased as the mixtures were cooled, and finally the peaks for the β form disappeared.…”

Influence of high pressure on the relative permittivity of oleic acid

“…While the first maximum may be associated with the reorientation of the internal structure, the second seems to correspond to the solidification process, as reported in [10]. On the other hand, the peak is strongly correlated with the scattering of light maximum which could be considered as an initialisation of the embryos of the new phase [15]. As shown in [16], an optical observation revealed no visible changes to the structures when the first temperature maximum occurs.…”