Optimisation of Supercritical CO2 Extraction of Red Colour from Roselle (Hibiscus Sabdariffa Linn.) Calyces

Abstract

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 usedto 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 %.