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Extraction of Bioactive Compounds from Leaves of Lawsonia inermis by Green Pressurized Fluids

Supercritical carbon dioxide and microwave-assisted hydrothermal methods were investigated for extraction of bioactive components of leaves of Lawsonia inermis (henna), a world renowned source of natural hair dye component called lawsone (2-hydroxy-1,4-naphthoquinone). Results showed that the use of supercritical carbon dioxide was selective to extraction of non-polar compounds such as essential oils, and the recovery of lawsone was low. However, using hot and compressed water as a solvent, a maximum recovery of lawsone of about 76.2% could be obtained at 120°C and extraction time of 30 min. At higher temperatures and longer treatment time, the yield and recovery decreased due most likely to the degradation of the target compounds at severe conditions. Moreover, the highest composition of lawsone close to 24% was obtained at microwave power of 600 W in irradiation time of 1 min. Mild hydrothermal conditions assisted with microwave heating are recommended in order to obtain high recovery of lawsone. Direct microwave heating of the polar components and solvent could lead to rapid extraction of the target compounds.