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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 > or = 256 and 32 microg/ml for HD and SD, respectively) than those obtained by SE-SD and SFE-SD (MICs > or = 4 microg/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 microg/ml.

The kinetics of supercritical fluid extraction of valuable substances from plants depends on both extract solubility in the solvent (or phase equilibrium between the matrix and the solvent) and mass transfer resistances, particularly the resistance inside vegetable material. Different mathematical models for supercritical fluid extraction have been published in the last decades and it can be therefore difficult to choose the most suitable model for particular extraction. In this chapter, simple criteria based on time constants of mass transfer and characteristic time of equilibrium extraction are presented, two most frequent types of models for supercritical extraction from plants are mentioned with references to the literature, and the factors influencing scale-up of the process are discussed.

Most applications of the photochromic technique of flow visualization have involved elaborate or expensive equipment. A simple, inexpensive application of the technique is described applied to a study of the fluiddynamics phenomena involved in mass transfer across a liquid gas interface. Essentially the set-up requires only a stirred beaker with photochromic dye solution, several relatively inexpensive sources of illumination (no laser) and a 35mm still camera or, alternatively, a movie camera. The analysis of the trace patterns photographed as described and the association between the flow pattern observed and the expected heat and mass transfer mechanisms is discussed.