Optimization of roselle seed in supercritical carbon dioxide

Abstract

Hibiscus sabdariffa (Roselle) seeds are high in proteins, unsaturated fatty acids, good source of minerals and antioxidants especially rich in gamma tocopherol. It reserves nutritional, industrial and pharmaceutical importance. To date, studies on the Roselle seed extraction are using conventional solvent extraction which usually take very long and is not favorable to extract active compound from heat sensitive samples. In this study, supercritical carbon dioxide (SC-CO2) extraction was applied for extraction of oil from Roselle seeds at temperature range of 40°C to 80°C and pressure of 20 MPa to 30 MPa. The effects of temperature and pressure on the extraction yield, solubility of oil and gamma tocopherol content were determined. The optimization of Roselle seed oil extraction process was conducted using the response surface methodology in order to obtain the highest yield and gamma tocopherol content. Roselle seed with low moisture content of 8.03% were used to prevent the moisture from acting as mass transfer barrier. Particle size of 300 |im and SC-CO2 flow rate at 5 ml/min was chosen for extraction and performed at 180 minutes constantly throughout this study. The overall oil yield increased with increased in pressure and temperature. While a reverse effect was observed with continuous rising of temperature. The highest Roselle seed oil recovery of 16.17% was obtained at 30 MPa and 40°C. The highest gamma tocopherol concentration of 5.6 mg per 100 g of extracted Roselle seed oil was observed at a low temperature of 40°C. The optimum extraction condition for Roselle seed oil was observed at pressure of 30MPa and temperature of 40°C. According to the analysis of variance, the coefficient determination R2 for Roselle seed extraction oil yield and gamma tocopherol were 0.9723 and 0.9754 of the total variance is explained by the secondorder polynomial model, indicating a good correlation and agreement between the experimental and predicted values. In the experimental range, the results showed that the Roselle seed oil yield, gamma tocopherol content and solubility are significantly influenced by temperature and pressure.