Sébastien Jubeau

Selective extraction from microalgae Nannochloropsis sp. using different methods of cell disruption.

This work studies the extraction of intracellular components from microalgae Nannochloropsis sp. with application of different cell disruption techniques, including pulsed electric field (PEF) (20kV/cm, 1-4ms, 13.3-53.1kJ/kg), high voltage electrical discharge (HVED) (40kV/cm, 1-4ms, 13.3-53.1kJ/kg), ultrasonication (USN) (200W, 1-8min, 12-96kJ/kg), and high pressure homogenization (HPH) (150MPa, 1-10 passes, 150-1500kJ/kg). The data evidence that electrically based disruption techniques (PEF and HVED) allowed selective extraction of water soluble ionic components and microelements, small molecular weight organic compounds and water soluble proteins. Microscopic and sedimentation stability analyses have shown that microalgae cells in HVED-treated suspension were noticeably agglomerated and could be easily settled in centrifuge. The electrically based disruption techniques were ineffective for delivery of pigments (e.g., chlorophylls or carotenoids) and their extraction required subsequent application of more potent disruption techniques. The obtained data have shown that HPH disruption technique was the most effective; however, this mode required the highest power consumption.

Highly valuable microalgae: biochemical and topological aspects

The past decade has seen a surge in the interest in microalgae culture for biodiesel production and other applications as renewable biofuels as an alternative to petroleum transport fuels. The development of new technologies for the culture of these photosynthetic microorganisms and improved knowledge of their biochemical composition has spurred innovation in the field of high-value biomolecules. These developments are only economically viable if all the microalgae fractions are valorized in a biorefinery strategy. Achieving this objective requires an understanding of microalgae content and the cellular localization of the main biomolecular families in order to develop efficient harvest and sequential recovery technologies. This review summarizes the state of the art in microalgae compositions and topologies using some examples of the main industrially farmed microalgae.

Separation and fractionation of exopolysaccharides from Porphyridium cruentum

In this work the extraction of EPSs from culture media of Porphyridium cruentum, by dialysis, solvent-precipitation with 3 polar alcohols (methanol, ethanol and isopropanol) and membrane separation techniques has been studied. Diafiltration (DF) using a membrane with a 300 kDa molecular weight cut off was the most efficient technique compared to solvent-extraction and dialysis methods. After extraction, EPS fraction was characterized in terms of rheological properties and biochemical content. The product exhibited shear thinning behavior and a critical overlap concentration equal to 0.6 g/L. The monosaccharide composition was investigated after acidic hydrolysis. Xylose, galactose, glucose and glucuronic acid were identified as the main constitutive monomers.

Physicochemical factors affecting the stability of two pigments: R-phycoerythrin of Grateloupia turuturu and B-phycoerythrin of Porphyridium cruentum.

Phycoerythrin is a major light-harvesting pigment of red algae, which could be used as a natural dye in foods. The stability of R-phycoerythrin of Grateloupia turuturu and B-phycoerythrin of Porphyridium cruentum in relation to different light exposure times, pHs, and temperatures was studied. Regarding the light exposure time, after 48h, the reduction in concentrations of B-phycoerythrin and R-phycoerythrin were 30±2.4% and 70±1%, respectively. Phycoerythrins presented good stability from pH 4 to 10. At pH 2, the reduction in concentration was 90±4% for B-phycoerythrin and 40±2.5% for R-phycoerythrin while, at pH 12, the phycoerythrins were degraded. Phycoerythrins showed good stability toward temperature, up to 40°C. At 60°C, the reduction in concentrations of B-phycoerythrin and R-phycoerythrin were 50±3.4% and 70±0.18%, respectively. Moreover, the best conditions of storage (-20°C) were determined.

Optimization of bead milling parameters for the cell disruption of microalgae: process modeling and application to Porphyridium cruentum and Nannochloropsis oculata.

A study of cell disruption by bead milling for two microalgae, Nannochloropsis oculata and Porphyridium cruentum, was performed. Strains robustness was quantified by high-pressure disruption assays. The hydrodynamics in the bead mill grinding chamber was studied by Residence Time Distribution modeling. Operating parameters effects were analyzed and modeled in terms of stress intensities and stress number. RTD corresponded to a 2 CSTR in series model. First order kinetics cell disruption was modeled in consequence. Continuous bead milling was efficient for both strains disruption. SI-SN modeling was successfully adapted to microalgae. As predicted by high pressure assays, N. oculata was more resistant than P. cruentum. The critical stress intensity was twice more important for N. oculata than for P. cruentum. SI-SN modeling allows the determination of operating parameters minimizing energy consumption and gives a scalable approach to develop and optimize microalgal disruption by bead milling.

Filterability of exopolysaccharides solutions from the red microalga Porphyridium cruentum by tangential filtration on a polymeric membrane

ABSTRACT The red microalga Porphyridium cruentum is exploited industrially for its exopolysaccharides (EPS) and pigments production. EPS produced by P. cruentum are partially released and dissolved into the surrounding environment, they can be recovered from the culture medium after removing the cells. This paper presents a parametric study of the ultrafiltration of EPS solutions on organic membrane. The EPS solutions were produced in conditions representative of an industrial production. They were filtered at lab-scale on a flat, PES 50 kDa MWCO membrane in a complete recirculation mode of permeate and retentate. Permeate flux-transmembrane pressure (TMP) curves were established up to the limiting flux for the filtration of solutions with various values of concentration in EPS (0.10–1.06 kg GlcEq m–3), fluid tangential velocity (0.3–1.2 m s–1) and temperature (20°C and 40°C). The reversible and irreversible parts of fouling were evaluated for each experiment and the critical flux was determined for an intermediate EPS concentration (0.16 kg GlcEq m–3). The results showed that EPS solutions had a strong fouling capacity. When filtering the lowest concentrated solution (0.10 kg GlcEq m–3) with moderate fouling conditions, the overall fouling resistance was approximately half of the membrane and the share of irreversible/reversible fouling was 88% and 12%. However, the part of reversible fouling becomes predominant when approaching the limiting flux. Permeate fluxes which were obtained allow to estimate that a VRR of approximately 10 could be obtained when concentrating EPS solutions using PES membranes in flat or tubular modules but not in spiral-wound. GRAPHICAL ABSTRACT