EXTRACTION OF AROMATIC AND MEDICINAL PLANTS WITH SUPERCRITICAL CARBON DIOXIDE

摘要

Aromatic and medicinal plants are usually extracted with organic solvents, such as hexane, acetone, methanol, ethanol, and methylene chloride. Soluble inorganic solvent substances are recovered by evaporating the solvent, preferably by vacuum distillation. Plant extracts obtained in this way are called oleoresins. Water, steam-water and steam distillation are the most frequently used methods for isolation of volatile constituents from plants. These constituents are hydrophobic substances called essential oils (Lawrence, 1995). Traditional extraction methods with organic solvents have several disadvantages. Most organic solvents are toxic, thus their residues in the extracts must be very low, usually 5-30 ppm or less. Also, during the solvent evaporation process the most volatile components in the extracts, which sometimes are very important for aroma formation, are lost. Moreover, oleoresins do not satisfy the growing demand for natural ingredients, which are supposed to be absolutely natural, i.e. produced without chemicals. Conventional extraction methods are not suitable for fractionation of extracts; therefore additional time-consuming and high-cost steps are required (Stahl et al., 1988). Fractions of aromatic and spicy plants can be successfully separated by changing extraction pressure and temperature (Nguyen et al., 1992; Dauksas et al., 1999).