Optimisation of supercritical CO2 extraction of red colour from roselle (Hibiscus Sabdariffa Linn.) calyces

Roselle (Hibiscus sabdariffa Linn.) is a local tropical plant widely cultivated in Malaysia. Roselle produces red edible calyces which contain intense red pigments of anthocyanins. Supercritical fluid extraction with carbon dioxide (CO2) is a particularly suitable isolation method for natural materials and gives an alternative to replace the mass usage of non-polar organic solvents in conventional methods. The advantage of using CO2 as solvent is that no organic solvent residual inside the extracted sample since CO2 is in gas form at room temperature. The red colour extract by using CO2 is easier to be separated by decompression and has high recovery percentage. The objective of this research was to optimise the supercritical carbon dioxide (SC-CO2) extraction conditions for obtaining the maximum yield of red colour extract. SC-CO2 extraction of red colour of roselle was performed with ethanol as modifier at the pressures of 8, 10 and 12 MPa, temperatures of 50, 60 and 70 °C while the percentage of modifier flow rates was at 5, 7.5 and 10 %. Full 33 factorial design was used to optimise operating conditions for the extraction yield of roselle calyces in SC-CO2.The other parameters were kept constant, such as total flow rate of CO2 and modifier (6 mL/min), ratio of modifier (75 % of ethanol), the average particle size used (350 μm) and extraction regime (70 min). The findings revealed that the extraction yield was significantly influenced by three main effects investigated in this study, with p-value smaller than 0.05. The optimum operating conditions obtained for SC-CO2 extraction of red colour extract were 8.90 MPa, 70 °C, and 9.49 % with predicted percentage yield of 26.73 %