Extraction of astaxanthin from Haematococcus pluvialis

Abstract

The astaxanthin extraction work comprised two main objectives. The first objective described the fundamental information of solubility of astaxanthin in supercritical carbon dioxide. From this first part we found that most supercritical CO₂ (SC-CO₂) extraction for astaxanthin extractions from H. pluvialis were operated at the mass transfer limitation, resulting in long extraction time requirement to obtained similar astaxanthin recovery, compared with other organic solvent extraction methods. This led us to the second objective to examine other extraction methods for extraction of astaxanthin from Haematococcus pluvialis such as y ultrasound-assisted and microwave-assisted organic solvent extractions. In the first section, the dynamic method was employed to determine the solubility of astaxanthin in SC-CO₂. The results demonstrated that the solubility of astaxanthin increased with pressure in the range of 20-40 MPa because of an increasing density of CO₂ at higher pressure which allowed a better contact between the solute and solvent. An increase in temperature in the range of 40-80 ℃ also enhanced the solubility of astaxanthin in spite of the drop in CO₂ density. This was because an increase in temperature raised the vapor pressure of solute which allowed a faster sublimation of astaxanthin, and this effect was believed to overcome the drop in CO₂ density. The experimental solubility data of astaxanthin was fitted to three selected models, among the, the equation of state (Peng Robinson) was found to best describe the solubility of astaxanthin over the entire range of temperature and pressure examined in this work. Such optimal solubility model was employed to evaluate the extraction efficiency of the previously reported experimental extraction data in literature. In SC-CO₂ extraction process, the solubility of astaxanthin from H. pluvialis was limited by to the mass transfer, causing long extraction time required for the process. In the second section, the various extraction techniques were examined for astaxanthin extraction from Haematococcus pluvialis. The parameters such as solvent properties, time and temperatures were found to affect the level of astaxanthin recovery. Acetone was found to provide the highest astaxanthin content in the extract. The microwave-assisted extraction method with acetone as solvent achieved the highest amount of astaxanthin content (74% extraction efficiency at 75 ℃) within a very short extracting time (5 min). To reach a similar level of extraction efficiency, the ultrasound-assisted extraction with acetone as solvent required an extended extraction time (45 min), but this could lower the temperature down to 45 ℃