Impact of harvesting via flocculation on protein yield from Chlorella vulgaris following pulsed electric field and high-pressure homogenization treatments

Abstract

The growing interest in sustainable biomass sources has encouraged research on microalgae, particularly focusing on improving the efficiency of cell separation and extraction processes. Currently, the harvesting step is primarily performed by centrifugation, which requires high energy consumption, especially for large-scale cultivation volumes. Therefore, this study aimed to explore coagulation/flocculation as an alternative harvesting method for Chlorella vulgaris, using FeCl₂, FeCl₃, and chitosan. Additionally, this study aimed to evaluate the effect of the different flocculants on subsequent protein extraction, comparing extraction yields obtained by pulsed electric field (PEF) and high-pressure homogenization (HPH) treatment for the first time. The results indicated that FeCl₃ had the highest flocculation efficiency, reaching over 99% with a lower dosage than the other flocculants (200 mg L⁻¹). Although FeCl₃ achieved the highest flocculation efficiency (over 99% at a low dosage of 200 mg·L⁻¹), the subsequent protein extraction yields were lower compared to centrifuged biomass. Protein recovery from FeCl₃-flocculated biomass reached only 9.22% of cell dry weight (CDW) with HPH and 0.5% of CDW with PEF, whereas centrifugation resulted in higher yields of 49.4% and 19.5% of CDW, respectively. These results indicate that while floc formation is effective for biomass harvesting, it may hinder protein extraction and reduce biomolecule recovery. Additionally, the protein profile analyzed by SDS-PAGE confirmed the negative impact of using flocculants, showing a disappearance or reduction of bands.