Applications of supercritical fluids in food science

Abstract

The choice of carbon dioxide as the supercritical fluid for chromatography and extraction is often concerned with its low cost, non-toxicity, inertness and availability in high purity. While these requirements are indeed valid, the range of analytes to which supercritical carbon dioxide can be applied is limited to non-polar—moderately polar analytes. While this may be acceptable to demonstrate the effectiveness of supercritical fluid chromatography (SFC) and/or supercritical fluid extraction (SFE), frequently it can provide a major limitation for real samples such as foodstuffs. Initial investigations of the use of modified carbon dioxide have met with some success. This typically involves the addition, via a second pump or a premixed cylinder, of an organic modifier (entrainer), often methanol. The addition of the modifier acts to increase the solvent strength of the supercritical carbon dioxide and to act as a competitor with adsorbed analytes for active sites on the matrix (Hills et al, 1991). An alternative approach to facilitate extraction and/or chromatography of polar analytes involves chemical derivatization. This may have the effect of reducing the polarity of the target analyte while increasing its solubility in supercritical carbon dioxide. In chromatography this would have the effect of shortening the retention time and improving peak tailing, whereas in extraction the additional benefit of chemically derivatizing the active sites to prevent resorption of the analyte is possible.