Growth Rate of Pressure‐Induced Triolein Crystals

Abstract

In pressure-induced crystal growth of triolein from melt at pressures up to 300 MPa and at temperatures between 283.16 and 293.16 K, we can distinguish three different crystal morphologies. Raman spectroscopy indicates that they are related to different polymorphic structures. Switching from the most stable to a less-stable structure implies a jump in the growth rate to a maximum value. As pressure increases, the growth rate decreases indicating that the growth is transport limited. Measurements at different temperatures show that the growth rate is mainly governed by pressure. In a certain parameter range, we observe crossnucleation to crystals with a higher growth rate. These crystals have a Raman fingerprint not yet described in the literature.

Melting Curves of Triolein Polymorphs

“…Briefly, the sample was placed into carriers described by Roßbach et al (2019) and Ferstl et al (2011). The sample was deposited between two transparent disks made of polymethyl methacrylate (PMMA) with a diameter of 10 mm, which were fixed into a holder with a central drilling of 8 mm diameter.…”

“…The crystals were detected as described by Roßbach et al (2019), i.e. a microscope (ZEISS STEMI SV 6, Oberkochen, Germany) with variable magnification…”

“…1b) or β 0 -crystals ( Fig. 1c) can be generated, see Roßbach et al (2019) 3. This pressure was kept constant to let the respective crystals grow.…”

“…It depends on the crystalline structure, which in turn is affected by the polymorphic form and the crystallization kinetics (Narine and Marangoni, 1999;Sato, 2018). Apart from thermal processing, it can also be adjusted by applying high pressures (Ferstl et al, 2010(Ferstl et al, , 2011Roßbach et al, 2019). In fact, high-pressure treatment of food and food ingredients has become popular in the food industry.…”

“…Despite the aforementioned studies, our knowledge on the impact of high pressures on triacylglycerol crystals seems to be still in its infancy. Apart from the unidentified crystal form recently reported by Roßbach et al (2019), there remain a number of other open questions like the following ones: Ferstl et al (2010) only determined the melting curve of the most stable polymorphic triolein form. The melting curves of the other polymorphic forms remain unknown.…”