Lipid extraction from Nannochloropsis oceanica biomass after extrusion pretreatment with twin-screw extruder: optimization of processing parameters and comparison of lipid quality

The objective of this work was to evaluate the effects of extrusion pretreatment on the efficiency of lipid extraction and the quality of lipid extracted from the microalga Nannochloropsis oceanica. Five processing parameters of extrusion pretreatment using a twin-screw extruder were studied: die configuration, distance from the internal surface of the die to the end of the screw (delta), temperature, screw rotation speed, and the water content of biomass. The results showed that die configuration, delta, and the water content of the biomass were vital factors affecting lipid extraction efficiency. After the pretreatment of extrusion, the extraction time was shortened from 10 h to 20 min, and the amount of solvent used was reduced to one-third of that without pretreatment. The content of polyunsaturated fatty acid (PUFA) in crude lipid increased by over 30 percent of those components without pretreatment, especially for eicosapentaenoic acid (EPA), which increased by 37.45%. In addition, the unsaponifiable content and acid value of the crude lipid extracted from the extruded microalga decreased significantly, which would facilitate further refining processes.