Supercritical extraction of unsaturated products. Degradation of beta-carotene in supercritical extraction processes

Supercritical carbon dioxide is a promising solvent for the extraction and crystallization processes of natural compounds, especially thermolabil comp ounds. It is recognized as exhibiting powerful advantages over conventional solvents. However, so far a crucial point has been ignored, the possible o xidation of unsaturated compounds due to the presence of oxygen in high pur ity carbon dioxide used in these processes. The highest purity grade of com mercial carbon dioxide is approximate to 2 mg/l STP. Taking into account th at the solubility of most natural compounds is less than or equal to 0.1%, this means that the oxygen/compound concentration ratio would be high. To t est this drawback, the extraction of p-carotene with supercritical carbon d ioxide was studied. The p-carotene solubility was found to be 3.8 mg/kg at 30 MPa and 40 degreesC. Therefore, 263 kg of carbon dioxide would be needed to yield 1 g of beta -carotene. That meant a 9 mol oxygen/mol beta -carote ne ratio. Results presented here suggest that beta -carotene was oxidized d uring the extraction process. (C) 2000 Elsevier Science B.V. All rights res erved.