Mathematical modelling of supercritical CO2 extraction of volatile oils from aromatic plants

The modelling of the experimental data of the extraction of the volatile oil from six aromatic plants (coriander, fennel, savoury, winter savoury, cotton lavender and thyme) was performed using five mathematical models, based on differential mass balances. In all cases the extraction was internal diffusion controlled and the internal mass transfer coefficienty (k(s)) have been found to change with pressure, temperature and particle size. For fennel, savoury and cotton lavender, the external mass transfer and the equilibrium phase also influenced the second extraction period, since k(s) changed with the tested flow rates. In general, the axial dispersion coefficient could be neglected for the conditions studied, since Peclet numbers were high. On the other hand, the solute-matrix interaction had to be considered in order to ensure a satisfactory description of the experimental data

Comparison of chemical composition and antibacterial activity of Nigella sativa seed essential oils obtained by different extraction methods

Nigella sativa L. seed essential oils obtained by hydrodistillation (HD), dry steam distillation (SD), steam distillation of crude oils obtained by solvent extraction (SE-SD), and supercritical fluid extraction (SFE-SD) were tested for their antibacterial activities, using the broth microdilution method and subsequently analyzed by gas chromatography and gas chromatography–mass spectrometry. The results showed that the essential oils tested differed markedly in their chemical compositions and antimicrobial activities. The oils obtained by HD and SD were dominated by p-cymene, whereas the major constituent identified in both volatile fractions obtained by SD of extracted oils was thymoquinone (ranging between 0.36 and 0.38 g/ml, whereas in oils obtained by HD and SD, it constituted only 0.03 and 0.05 g/ml, respectively). Both oils distilled directly from seeds showed lower antimicrobial activity (MICs ≥ 256 and 32 μg/ml for HD and SD, respectively) than those obtained by SE-SD and SFE-SD (MICs ≥ 4 μg/ml). All oil samples were significantly more active against gram-positive than against gram-negative bacteria. Thymoquinone exhibited potent growth-inhibiting activity against gram-positive bacteria, with MICs ranging from 8 to 64 μg/ml

Lipase activity enhancement by SC-CO2 treatment

The activity of lipases from porcine pancreas, Candida antartica recombinant from Aspergillus oryzae, Candida cylindracea (immobilized), Penicilium roqueforti, Aspergillus niger, Rhizopus arrhizus, Mucor miehei (two types of immobilization), and Pseudomonas cepacia (two types of immobilization) was studied after using them as biocatalysts of blackcurrant oil hydrolysis under SC-CO2 conditions. The reaction was performed at 40°C and 15 MPa in a continuous-flow reactor. Increased relative activity of all used lipases after the hydrolytic reaction was observed. The most remarkable increase in the activity was noted for the lipase from Rhizopus arrhizus which was increased by more than 50 times. The highest activity was shown by Lipozyme®, lipase from Mucor miehei, immobilized on macroporous resin. Both treated and untreated Lipozyme® were used as biocatalysts in hydrolytic resolution of the racemic cis- or frani-isomers of 2-(4-methoxybenzyl) cyclIohexyl acetates. Satisfactory reaction yields (40 %) and excellent enantiomeric purity of the products (E = 472) were obtained when hydrolysis of the frans-isomer of 2-(4-methoxybenzyl)cyclohexyl acetate was catalyzed by Lipozyme® treated with SC-CO2. © 2008 Verlag der Zeitschrift für Naturforschung, Tübingen

Martini Force Field Parameters for Glycolipids

<p>We present an extension of the Martini coarse-grained force field to glycolipids. The glycolipids considered here are the glycoglycerolipids monogalactosyldiacylglycerol (MGDG), sulfoquinovosyldiacylglycerol (SQDG), digalactosyldiacylglycerol (DGDG), and phosphatidylinositol (PI) and its phosphorylated forms (PIP, PIP2), as well as the glycosphingolipids galactosylceramide (GCER) and monosialotetrahexosylganglioside (GM1). The parametrization follows the same philosophy as was used previously for lipids, proteins, and carbohydrates focusing on the reproduction of partitioning free energies of small compounds between polar and nonpolar solvents. Bonded parameters are optimized by comparison to lipid conformations sampled with an atomistic force field, in particular with respect to the representation of the most populated states around the glycosidic linkage. Simulations of coarse-grained glycolipid model membranes show good agreement with atomistic simulations as well as experimental data available, especially concerning structural properties such as electron densities, area per lipid, and membrane thickness. Our coarse grained model opens the way to large scale simulations of biological processes in which glycolipids are important, including recognition, sorting, and clustering of both external and membrane bound proteins.</p>