Supercritical fluid extraction phenolic acids

Supercritical fluid extraction has been applied to extract phenolic acids from a variety of plant samples. It uses high-pressure to force carbon dioxide to be a mixture of liquid and gas phases, which is called a supercritical fluid. The liquid and gas phase mixture of carbon dioxide can more readily permeate the sample matrix than only the gas phase of carbon dioxide. The compounds solublized in the liquid phase of carbon dioxide are extracted from the sample matrix and collected after they elute from the outlet of the system. The biggest advantage of supercritical fluid extraction is that there is no, or less, organic solvent involved in the extraction, due to the use of carbon dioxide supercritical fluid as the major solvent.. The carbon dioxide readily evaporates as gas phase at the system outlet. Thus, unlike other solvent extraction methods, there is no evaporation step for the extraction, making this an environmentally friendly method. However, the system is much more expensive and delicate than the other novel technology extraction... 

For biological evaluation larger quantities of component phenols and their constituents may be required and where different components such as alkylresorcinols and anacardic acids co-occur, an initial solvent separation may prove desirable. Mild extraction methods, such as supercritical fluid extraction with carbon dioxide, [1,219,220], followed by phase separation [221], preparative TLC [222], or column chromatography [223] may be valuable for complex mixtures. 

Most of the extraction techniques of phenolic compounds from vegetables are based on ultrasound-assisted extraction (UAE) [27,44,45], In addition, other techniques have been successfully applied to the pretreatment of phenolic compounds in fruits and vegetables, including pressurized liquid extraction (PLE) [46], solid-phase extraction (SPE) [47], supercritical fluid extraction (SFE) [48], microwave-assisted extraction (MAE) [49], rotary shaker-assisted extraction (RAE), [50] and QuEChERS (acronym of quick, easy, cheap, effective, rugged and safe) [51], as can be observed in Tables 16.3 and 16.4. In some cases, an acid treatment [52] was applied to hydrolyze the glycosides in order to determine the content of free and conjugated flavonoids as aglycons. 

By devising supercritical fluid based schemes to remove the byproduct from the condensation reactions, higher conversions are achievable. Even though water does not show high solubility in supercritical carbon dioxide, other condensation products (i.e., phenol, acetic acid) which may have higher solubility in carbon dioxide may be extracted from the reaction mixture with carbon dioxide and increase conversion. Removal with carbon dioxide would be a desirable path compared to vacuum methods employed in traditional condensation polymerizations. 

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