Extraction of plants (on the example of spices)

Organic foods require processing without the addition of external material. Supercritical fluid extraction (SFE) using carbon dioxide (CO2) is a particularly suitable isolation method. A natural plant extract, free from chemical alterations brought about by heat and water, and without solvent residues and other artifacts can be obtained by this method. Carbon dioxide is non-toxic, non-explosive, readily available and easily removed from the extracted products.

All products characterized by their internal content are claimed by the market consumers to have a reproducible and stable quality. The ground spice products made in the traditional way are frequently not corresponding to the requirements concerning reproducibility, stability and recently also for microbiological point of view. Technological solutions are sought that insure these properties of the products and satisfy the standards in a more reproducible way.

Beyond the supply and demand relations there are situations in Hungary when sale problems occur because the technology is limited in producing standardized spice products. Consequently the ware is not sold, which means it looses further from its internal content.

For extraction of spices a variety of solvents, including alcohols, acetone and hexane can be used. However, these organic solvents leave adsorbed residues behind and elevated temperatures at the desolventization process can cause chemical modifications of the oleoresins. Governmental regulation of these solvents varies from country to country. The solvent residues must be reduced to very small concentrations, generally in the range of 25-30 ppm or less.

Supercritical fluids are gases with properties between that of a "normal" gas and a liquid. Variation of pressure changes properties of supercritical fluids continuously from more gas-like behavior to more liquid-like behavior. This behavior may lead to new technologies in processing natural materials (extraction and purification), in processes related to the environment (destruction of waste with supercritical water), and in reaction engineering (hydrogenation with mixtures of hydrogen and supercritical carbon dioxide). Applications in biotechnology may appear in downstream processing and enzyme catalyzed reactions.

Supercritical fluids produce practically solvent-free products and avoid deteriorating reactions. Process temperatures are low to very moderate. Solvent handling is favorable because it can be easily and totally removed, it is readily available and cheap, and it is accepted and part of the environment (water, carbon dioxide). Even then, solvent losses are minimal when compared to ordinary men's activities for these substances, since the solvent is recycled.

Situations where supercritical fluids may be useful emerge from the effects which supercritical fluids have on pure compounds and mixtures. Supercritical fluids change compound properties, phase equilibria, chemical equilibria, and related rate processes, as has been discussed in many publications.

The product of a supercritical extraction of a spice is normally not solid. The liquid spice-products are more stable than the classic forms, after a longer storage period they loose their internal content in a slighter degree; The new liquid spice-products have a more reproducible quality. Both for the private user and the food technology the reproducibility means surplus value ; The new liquid spice products contain the characteristic aroma, taste and odour; Substances are in a solution form. During their utilization a smaller quantity is required for reaching the same effect; The standardization of the new liquid spice products means that the composition, the characteristic values are controlled during the producing process , but simultaneously they represent the secret of the technology. In consequence hopefully till for a long time  the falsification, dilution or any other market fraud will be prevented by the manufacturing process.

 

   
© BME, Research Group on Supercritical Fluids, 2015