Optimization of supercritical carbon dioxide extraction of astaxanthin from Haematococcus pluvialis

In this study, experimental design was employed in order to investigate the effects of operating conditions on supercritical carbon dioxide extraction of astaxanthin from Haematococcus pluvialis. The factors investigated were the operating temperature in range of 40-80 ํC, the operating pressure in range of 300-500 bar, and the extraction time in range of 1-4 hours. The results showed that the main effect of operating pressure, the main effect of extraction time, and the interaction effect between operating temperature and operating pressure were significant factors for the astaxanthin yields. From the response surface model of the experimental data, an optimal condition for astaxanthin content was found to be at the temperature of 90 ํC, the pressure of 640 bar, the extraction time of 2.9 hours and amount of astaxanthin extract of 22.66 mg/g. This condition was the extrapolated result and therefore would not be accurately predicted. Thus the optimal condition was proposed within the range of this experiment to be at the temperature of 70 ํC, the pressure of 500 bar, and the extraction time of 4 hours, which yielded the amount of astaxanthin extract of 23.04 mg/g dry algae. For the effect of experimental conditions on antioxidant activity, IC[subscript 50], the concentration that gives a 50% reduction in the absorbance of the free radical ABTS, was used as a measure of the activity. The analysis of the results showed that interaction between operating temperature and operating pressure was the only significant factor affecting the extract antioxidant activity. The response surface analysis gave the conditions that yielded the minimum antioxidant activity of the extract. This condition was at the temperature of 50 ํC, the pressure of 354 bar, and the extraction time of 2.68 hours, in which the IC[subscript 50] was 2.18 mg/l. Therefore, the optimal condition recommended for SC-CO[subscript 2] extraction was at the temperature of 70 ํC, the pressure of 500 bar, and the extraction time of 4 hours