Microalgae cultivation and purification of carotenoids using supercritical anti-solvent recrystallization of CO2 + acetone solution

Zeaxanthin is a type of xanthophyll found in carotenoids, which is produced as a food supplement frequently used for human retinal protection. These works investigated growth rate and harvest of the sea water algal species of Nannochloropsis oculata (N. oculata) by in-door and out-door cultivations; stirred ultrasonic acetone extraction of zeaxanthin from; employed column fractionation to obtain zeaxanthin-rich elution; and then coupled it with supercritical carbon dioxide anti-solvent (SAS) precipitation to generate the highly pure submicron-sized zeaxanthin. The ultrasonic extract contained 38.2 mg/g of zeaxanthin and then the column elution fractionation increased the zeaxanthin content to 41% (410.3 mg/g) with a recovery of 82.3%. The SAS precipitation at 215 bar, 50 °C for 24 min of injection time enhanced the zeaxanthin content to 58% (582.4 mg/g) with a recovery of 67.2%. Experimental results showed that the amount of zeaxanthin increased with total SAS time and feed concentration had an effect of enlarging the precipitates due to agglomeration and accumulation. The SAS precipitation of the column purified algal solution demonstrated a production of micro/nano-sized lamellar particulates that contained high amounts of zeaxanthin.