The article discusses further research of the new high-pressure phase in triolein and in triolein mixed with methyl alcohol. The transformation from the initial isotropic state of liquid to the high-pressure phase in case of the mixture of triolein-alcohol was observed by us for the first time. In this study, we compare the phase transformation under pressure, both for oil and for oil-alcohol mixture. Spectra of Raman and UV-VIS absorption show that the application of pressure to triolein leads to partial irreversibility of the observed processes. That partial irreversibility is important for the food conservation methods based on high-pressure technology since triolein is a good model of the most of vegetable oils components.

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A high-pressure research on rapeseed oil and mixtures of rapeseed oil with methyl alcohol has been made. In all cases, at least one occurrence of the first order phase transition similar to that in castor oil was noticed [R.M. Siegoczyński, Reports of the Institute of Physics. No. 46, Publishing House of the Warsaw University of Technology (1998)]. Experiments were performed in a cylindrical chamber with a simple piston system, working together with 20 ton hydraulic laboratory press. The pressure in those experiments was approaching 1 GPa. Changes of pressure, volume, temperature and capacitance were recorded using an advanced data acquisition system. In this article, the changes of the relative electric permittivity ε r as function of pressure and also the compressibility of investigated liquids have been presented. Abnormal rise of the dielectric constant in the mixture of rapeseed oil with methyl alcohol was observed. These results suggest the occurrence of a new phase transition apart from the one observed earlier in rapeseed oil [A.J. Rostocki, R. Wiśniewski and T. Wilczyńska, J. Mol. Liq., in press].

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