Optimisation of supercritical carbon dioxide derived high-value botanical extracts of Melissa officinalis

Abstract

This project dealt with the acquisition of supercritical carbon dioxide (scG02) derived extracts from Melissa officinalis. The actuality of such extracts lies in the diversity of its components, which are relevant to the pharmaceutical, cosmetic, fragrance/flavour and food industries. Extractions were performed on selected dried plant material using a laboratory-scale supercritical fluid extractor. The runs were executed according to an orthogonal, rotatable statistical design in order to optimise conditions (pressure, temperature, duration) for a maximum yield of extract by computer-assisted surface response analysis. The relationship between the yield of extract and the principal process parameters enabled conclusions to be drawn about the mechanism of extraction. The volatile components are physically desorbed from the plant matrix as a result of the diffusivity of low-density (gas-like) sc-CO2, whereas the non-volatile components are chemically dissolved on account of the solvent strength of high-density (liquid-like) sc-CO2. An equation based on a dimensionless grouping of variables was derived to mathematically describe the extraction process in terms of all major contributing process parameters. The extracts were analysed by GC/MS and GC-GC/TOF-MS. A total of 204 components were identified, many of which correspond with those extracted by traditional methods and which are reported in the literature. The analytical results prove that component-rich botanical extracts can be obtained with sc- CO2 as extractant. In addition, the fluid warrants solvent free extracts and clean technology for sustained environmental protection.