The research is mainly oriented to two lines: extraction of biologically active compounds from various natural sources and enzymatic reactions in supercritical CO2. The common interest of these two lines is to fractionate the extraction or reaction product in order to obtain various products rich in particular compound or groups of compounds. Simultaneously, fundamentals of supercritical fluid extraction are studied to describe the processes by mathematical models.
Supercritical CO2 extraction has been widely studied as a modern, environmentally friendly method to separate natural products and high-added value compounds from plants provides several advantages over traditional extraction techniques. As the density and the solvent power of supercritical fluids are close to those of liquids and their transport properties are close to those of gases, they can penetrate into a porous solid material more effectively than liquid solvents. Moreover, after the extraction, the solute can be easily separated from the extract by decrease in pressure, in contrast to conventional extraction techniques using organic solvents which are difficult to remove completely from the extracts. The solvation power of supercritical fluid can be manipulated by changing pressure and temperature, which enables a selective extraction.
Knowledge of main features of the processes and their mathematical modelling facilitate their optimisation and scale-up.
Supercritical carbon dioxide (SC-CO2) is a suitable reaction medium for non-polar substrates like vegetable oils. Compared to conventional liquid solvents, the rate of heterogeneous reactions is higher due to the good transport properties of supercritical fluids, the CO2 can be easily separated from reaction mixture by decrease in pressure, and the products are not contaminated by toxic substances. Different enzymes, including lipases, have exhibited a sufficient activity and stability in SC-CO2, on condition that optimum moisture is maintained. This enables us to utilize the advantages of supercritical solvent and specificity of enzyme-catalyzed reactions.
Generally, plant extracts are complex mixtures of many compounds, and the desired substances are very often just minor components in them. In contrast to classical methods of extraction by organic solvents or steam distillation, supercritical extraction allows us to dissolve preferably required compounds by changing extraction pressure and temperature. However, this step is not selective enough to prevent co-extraction of other classes of substances. To obtain higher concentration of the desired compounds, a method of extract fractionation may be applied. An elegant method of supercritical extract fractionation is its gradual separation from the solvent in a series of separators maintained at different conditions (pressure and temperature). In each separator, the less soluble components precipitate from the mixture while the rest remains dissolved in CO2 and flows to the next separator where the fractionation is repeated at lower solvent power; the most soluble substances precipitate in the last separator.