Concentration and desalting of Tetraselmis suecica crude extract by ultrafiltration

Abstract

Downstream processing, encompassing molecule extraction and extract purification, is a critical step in microalgal biorefinery. This study focuses on the concentration and desalting of Tetraselmis suecica crude extract, which contains proteins, neutral carbohydrates, uronic acids, and pigments. The biomass was initially disrupted with a high-pressure homogenizer operating in moderate conditions (P = 300 bars and 2 passes). The liquid extract obtained was then desalted and concentrated by stirred-cell ultrafiltration. Two membranes, both made of polyethersulfone (PES) but with different molecular weight cut-offs (10 kDa and 30 kDa), were tested for this purpose. The filtration process lasted 3.15 ± 0.34 h, with the temperature maintained at 28 ± 3ºC. There was, therefore, a compelling need to reduce the ash content to facilitate valorization of the extracted proteins. Both membranes displayed time-dependent decreases in permeate flux, membrane permeability, and shear rate. The protein concentration of the permeate increased steadily over time, whereas the concentrations of ash and uronic acids remained constant during ultrafiltration. These results demonstrated the efficacy of both membranes for desalting the extract. After disruption, the ash content in the extract was initially high, at 35.5 ± 0.8% dry weight (DW), decreasing protein purity to 26.1 ± 0.3% DW. The 10 kDa membrane displayed superior molecule retention, resulting in an increase of protein concentration to 50 g.L-1 in the final retentate. The 10 kDa membrane eliminated 79.5 ± 0.5% of salts from the extract, potentially achieving the complete retention of proteins, pigments, and uronic acids; approximately 21.4 ± 3.6% of total carbohydrates were removed by this membrane.