Adsorbent-assisted supercritical CO2 extraction of carotenoids from Neochloris oleoabundans paste

Neochloris oleoabundans emerges as alternative source of bioactives that complies with the algae-based biorefinery concept, which consists of a platform that offers a multitude of algae bioproducts. The development of an integrated extractive processes in line with the green chemistry principles have motivated the use of Supercritical CO (scCO), as an alternative to toxic organic solvents, for the extraction of bioactives. However, process integration and optimization is challenging because microalgae are grown in liquid cultures, therefore is often necessary a drying step prior to scCO extraction. Moreover, this step is usually energy intensive and risks damaging the compound's bioactivity. An alternative is the simultaneous extraction process of the microalgae paste (containing around 70-80% water), nevertheless little information is available that explores this type of extraction. This work aims to explore the direct extraction of microalgae paste and to evaluate the effect of water on carotenoid extractions of N. oleoabundans. To study the extraction under a batch-wise system, an indirect extraction system was developed by mixing the microalgae paste with low cost adsorbents as support medium. Two types of silica gels, two different chitosans and active carbon were tested as adsorbents; sea sand was used as inert control. All of the materials showed different adsorbent capacity, being chitosan adsorbents those with higher capacity. However, oleoresin yield and recovery was negligible in a system with only scCO as a solvent and ethanol as co-solvent was required to improve the extraction yield. Although the overall oleoresin recoveries were low for all adsorbents (ranging from 2 to 10%), chitosan-assisted extraction showed the highest carotenoid recoveries (60-140% g/g) surpassing acetone benchmark extraction in case of chitosan microspheres. These results are interesting for the development of low energy consumption processes, since there is no need to dry the microalgal paste.Spanish Projects AGL2011-29857-C03-01, AGL2014-53609-P (MINECO, Spain) and ALIBIRD-CM, S2013/ABI-2728 (Comunidad de Madrid) and the European project MIRACLES (KBBE.2013.3.2-02: The CO2 algae biorefinery) are acknowledged for their financial support. Fabián A. Reyes would like to thank CONICYT-Chile for supporting his fellowship in CIAL-CSIC, Spain.Peer Reviewe