Purification of algal anti-tyrosinase zeaxanthin from Nannochloropsis oculata using supercritical anti-solvent precipitation

This work investigated the changes in content of algal zeaxanthin in submicronized precipitates generated from the supercritical anti-solvent (SAS) process of extracting microalgae Nannochloropsis oculata. Following a reverse phase elution chromatography, the particulates were successfully generated from feed solutions containing zeaxanthin that ranged from 0.4 to 0.8 mg/mL by a SAS process. The precipitation condition was set at 323 K and pressures ranged from 10 to 20 MPa. Experimental results of a three-factor center composite response surface method for the SAS process indicated that the size of the precipitates was significantly affected by the flow rate of carbon dioxide. The purity of zeaxanthin increased with increasing solvent flow rate and with reducing solution concentration. The recovery of zeaxanthin and the morphology of the precipitates was also examined. The content of zeaxanthin in submicronsized precipitates increased from 485.9 (48.6%) to 673.7 mg/g (67.4%). This work demonstrates that elution chromatography coupled with a SAS process is an environmentally benign method to recover anti-tyrosinase zeaxanthin from Nannochloropsis oculata as well as to generate submicrosized precipitates of the purest zeaxanthin from algal solutions.