Pef-assisted Supercritical CO2 Extraction of Pigments from Microalgae Nannochloropsis Oceanica in a Continuous Flow System

Abstract

This study aimed at evaluating the effect of pulsed electric fields (PEF) pre-treatment on the extractability of pigments (total carotenes, chlorophyll a) from microalgae Nannochloropsis oceanica by supercritical CO₂ (scCO₂) extraction. Aqueous microalgal suspensions (1% w/w) added with 10% ethanol were treated in a continuous flow unit with either PEF at different field strengths (10–30 kV/cm) and total specific energy inputs (20–100 kJ/kg), or scCO₂ at different pressures (8-20 MPa), with fixed temperature (35°C), CO₂/biomass ratio (53.3 kg_CO2/kg_DW) and contact time (7 min). Extracts from conventional solvent extraction process and PEF-assisted scCO₂ extraction were analyzed and compared with those achieved upon the application of single PEF and scCO₂ extraction processes. Results showed that in PEF-assisted extraction the recovery yield of the target compounds significantly increased with increasing the treatment severity, even though the effect of the field strength appeared less important than the energy input. After PEF treatment at 10 kV/cm and 100 kJ/kg, the extraction yield for total carotenes and chlorophyll a increased by 1.6 and 1.4 times, respectively. During single scCO₂ extraction process at 14 MPa the extraction yield for total carotenes and chlorophyll a increased up to 10.3 and 13.6 times, respectively, as compared to the untreated samples. The use of PEF prior to scCO₂ extraction remarkably increased the extractability of the two pigments showing a clear synergistic effect. The results obtained in this work suggested that the application of PEF prior to scCO₂ extraction could represent a suitable approach for the efficient recovery of pigments from microalgal biomass.