The free radical-scavenging activities of extracts of Aloe vera of leaf skin by supercritical CO2 extraction and solvent extraction were determined. An orthogonal array design matrix of L-9 (3(4)) was considered to optimize supercritical carbon dioxide extraction processing at a CO2 flow rate of 12-36 1 h(-1), 35-45 MPa and 32-50 degreesC. The optimum extracted yield of 1.47% was provided at 50 degreesC 36 l h(-1), 35 MPa and 20% of modifier of methanol. These four factors were all demonstrated to be significantly crucial in the supercritical carbon dioxide extraction operation, as two-variable interactions. The extracts of A. vera rind by supercritical carbon dioxide extraction and solvent extracts provided significantly higher free radical-scavenging activities of 33.5% and 39.7%, respectively, than extracts of A. vera gel extracted by ethanol with a free radical-scavenging activity of 14.2%. The inhibition percentage of extracts of A. vera and reference antioxidants followed the decreasing order: Trolox (76.8%) > ethanol extracts of A. vera skin (39.7%) > BHT (35.9%) > the extract of supercritical carbon dioxide extraction (33.5%) > alpha-tocopherol (25.6%) > ethanol extracts of A. vera pulp (14.2%). Compared to BHT and alpha-tocopherol, the extracts of A. vera skin, by supercritical carbon dioxide extraction and ethanol, showed stronger antioxidant activities. Components in the rind of A. vera are responsible for the higher antioxidant activity of A. vera extracts. (C) 2004 Elsevier Ltd. All rights reserved.
