Luc Marchal

Nitrogen limitation and changing solar conditions are both known to affect triacylglycerol (TAG) production in microalgae. This study investigates the optimization of TAG production with a continuous nitrogen‐limited culture of Nannochloropsis gaditana in simulated day–night cycles (DNc). The effect of DNc was first investigated in nitrogen‐deprived condition (i.e., batch culture), emphasizing a significant change in mechanical resistance of the strain during the night. The concept of released TAG, which shows how much of the TAG produced is actually recovered in the downstream stages, that is, after cell disruption, was shown here of interest. For a maximum released TAG, the optimum harvesting time was suggested as being 4 h into the night period, which minimizes the losses due to a too great cell mechanical resistance. The protocol for continuous nitrogen‐limited culture was then optimized, and a continuous nitrogen addition was compared to a pulsed‐addition. For the latter, nitrogen was supplied in a single pulse at the beginning of the light periods, while the bulk medium was supplied separately at a slow but constant dilution rate of . The pulse dose was calculated after the study of nitrogen consumption and TAG production/consumption during the DNc. The estimated released TAG for the pulsed‐addition of 1.4 × 10⁻³ kg/m²d found significantly higher than the one achieved in batch culture (0.3 × 10⁻³ kg/m²d) but lower than for continuous nitrogen addition which obtained the highest released TAG of .

Fucoxanthin is a brown-colored pigment from algae, with great potential as a bioactive molecule due to its numerous properties. This review aims to present current knowledge on this high added-value pigment. An accurate analysis of the biological function of fucoxanthin explains its wide photon absorption capacities in golden-brown algae. The specific chemical structure of this pigment also leads to many functional activities in human health. They are outlined in this work and are supported by the latest studies in the literature. The scientific and industrial interest in fucoxanthin is correlated with great improvements in the development of algae cultures and downstream processes. The best fucoxanthin producing algae and their associated culture parameters are described. The light intensity is a major influencing factor, as it has to enable both a high biomass growth and a high fucoxanthin content. This review also insists on the most eco-friendly and innovative extraction methods and their perspective within the next years. The use of bio-based solvents, aqueous two-phase systems and the centrifugal partition chromatography are the most promising processes. The analysis of the global market and multiple applications of fucoxanthin revealed that Asian companies are major actors in the market with macroalgae. In addition, fucoxanthin from microalgae are currently produced in Israel and France, and are mostly authorized in the USA.

Biocompatible extraction emerges recently as a means to reduce costs of biotechnology processing of microalgae. In this frame, this study aimed at determining how specific culture conditions and the associated cell morphology impact the biocompatibility and the extraction yield of β-carotene from the green microalga Dunaliella salina using n-decane. The results highlight the relationship between the cell disruption yield and cell volume, the circularity and the relative abundance of naturally permeabilized cells. The disruption rate increased with both the cell volume and circularity. This was particularly obvious for volume and circularity exceeding 1500 µm³ and 0.7, respectively. The extraction of β-carotene was the most biocompatible with small (600 µm³) and circular cells (0.7) stressed in photobioreactor (30% of carotenoids recovery with 15% cell disruption). The naturally permeabilized cells were disrupted first; the remaining cells seems to follow a gradual permeabilization process: reversibility (up to 20 s) then irreversibility and cell disruption. This opens new carotenoid production schemes based on growing robust β-carotene enriched cells to ensure biocompatible extraction.

Treatments with high-voltage electrical discharges (HVED) and high-pressure homogenization (HPH) were studied and compared for the release of ionic components, carbohydrates, proteins, and pigments from microalgae Parachlorella kessleri (P. kessleri). Suspensions (1% w/w) of microalgae were treated by HVED (40 kV/cm, 1–8 ms) or by HPH (400–1200 bar, 1–10 passes). Particle-size distribution (PSD) and microscopic analyses were used to detect the disruption and damage of cells. HVED were very effective for the extraction of ionic cell components and carbohydrates (421 mg/L after 8 ms of the treatment). However, HVED were ineffective for pigments and protein extraction. The concentration of proteins extracted by HVED was just 750 mg/L and did not exceed 15% of the total quantity of proteins. HPH permitted an effective release overall of intracellular compounds from P. kessleri microalgae including a large quantity of proteins, whose release (at 1200 bar) was 4.9 times higher than that obtained by HVED. Consequently, HVED can be used at the first step of the overall extraction process for the selective recovery of low-molecular-weight components. HPH can be then used at the second step for the recovery of remaining cell compounds.

Centrifugal Partition Chromatography (CPC) is a versatile support free chromatographic technique involving the distribution and transfer of solutes between at least two immiscible liquid phases according to their partition coefficient, that avoids irreversible adsorption of the analytes due to the absence of solid support and allows a total recovery of various injected samples. The introduction of the so-called displacement mode dedicated to the purification of ionizable compounds, as well as the development of modeling approaches [1] taking into account both hydrodynamic and mass transfer aspects have attracted increasing interest to the area. This communication describes the use of CPC in the pH-zone refining mode for the purification of two indolomonoterpenic alkaloids, namely vindoline and catharanthine, from an industrial extract of Catharanthus roseus. The scale up of the separation on various pilot-scale columns [2] was achieved thanks to a numerical model allowing the prediction of chromatograms, highlighting the potential of CPC for the industrial purification of high added value compounds. [1] Kotland A, Chollet S, Diard C, Autret JM, Marchal L, Renault JH. J. Chromatogr. A, 2015, 1391:80 – 87. [2] Kotland A, Chollet S, Diard C, Autret J.-M, Meucci J, Renault J.-H, Marchal L, J. Chromatogr. A, 2016, 1474, 59 – 70.