Subcritical water extraction of anthraquinones from roots of morinda citrifolia

Abstract

A technique of solvent-free extraction of anthraquinones, a group of antioxidant active compound from roots of Morinda citrifolia was proposed. The tecqnique utilizes subcritical water, or sometimes called pressurize hot water extraction (PHWE) as extraction medium. A series of extraction experiments were carried out at different conditions, i.e., temperatures of 150, 170, and 200 ํC and flow rates of 2, 3, 4, 5, and 6 ml/min, while the pressure remained fixed at 40 bars. The results of the study revealed that the extraction yield increases as the temperature increases and extraction rate increases as the flow rate increases up to 5 to 6 ml/min. The most suitable extraction condition was found to be at the temperature of 200 ํC and the flow rate of between 3 and 5 ml/min. A set of experiments at various flow rates suggests that the overall extraction mechanism was influenced by both mass transfer and solubility. In addition to the extraction study,the solubility of anthraquinones in subcritical water at various temperatures was also determined and a mathematical model was proposed. Comparing the extraction yields of subcritical water extraction with conventional method including maceration, soxhlet extraction, and ultrasonic assisted extraction, subcritical water extraction was found to achieve approximately 95 % recovery within only 2 h, whereas it takes extended time period of 72 h to achieve the only 80 % recovery. Although the use of ultrasound at 60 ํC was able to reduce the extraction time from 72 h to 2 h, it is still inferior to subcritical water extraction, which requires approximately the same extraction time as soxhlet extraction. Other than the quantitative analysis of anthraquinones extracted, the quality of the extract was also measured in term of antioxidant activity using a DPPH method. The results showed that antioxidant activity of the extracts obtained with subcritical water extraction was similar to that with soxhlet extraction and maceration and that there were no effects of the subcritical water temperature in the range tested. On the other hand, extracts obtained with ultrasonic assisted extraction showed the lowest antioxidant activity. All these have led to the conclusion that subcritical water extraction is a benign alternative for extraction of anthraquinones from the roots of Morinda citrifolia.