Biorefining of microalgae to prepare novel high added value ingredients
Résumé
The microalga Tetraselmis chuii is a promising source of various potentially valuable biomolecules. However, the extraction and the recovery of these compounds with improved quality remains a technological challenge due to the inherent problems linked to their availability and stability. In this study, water-soluble compounds, notably T. chuii proteins, were extracted by maceration, and recovered by membrane filtration. Firstly, the optimization of the maceration process was done by means of a design of experiments (DoE) with response surface methodology using Box-Behnken design. The effects of three operating parameters including solid/liquid ratio (0.5-7.5 g/L), pH (6-12), and temperature (25-45°C) were investigated. Secondly, ultrafiltration was applied on supernatant obtained after centifugation, testing membranes with different cut-off (3, 15, 50, 150 et 300 kDa). All membranes were compared based on their hydraulic performance, recovery and retention rates and selectivity. A high protein extraction yield (78.38%) was achieved under the following optimal aqueous extraction conditions : biomass concentration 7.5 g/L, 20°C and pH 12. Furthermore, soluble protein recovery was significantly affected by the three variables tested. Regardless of the membrane used, yellow permeates, poor in chlorophyll, were successfully produced. All filtrations using five membranes with different cut-off showed similar protein concentration levels with a purity index between 13 and 16%. In addition, filtration on a 300 kDa membrane showed a 67% increase of protein recovery in the retentate compared with other membranes. The study also concludes that increasing the cut-off of the membrane does not necessarily increase the permeate flux and the yield of proteins recovered in the permeate phase. Considering this conclusion and the highest protein yield of recovery obtained after maceration, a combination of this treatment and fractionation by ultrafiltration using a 300 kDa membrane cut-off would be the best route to achieve an enriched protein fraction for this species.