Production of Dunaliella salina biomass rich in 9-cis-β-carotene and lutein in a closed tubular photobioreactor

Performance of Dunaliella salina cultures outdoors in a closed tubular photobioreactor has been assessed. Optimization of conditions involved verification of the effect of several determining factors on the yield of both biomass and carotenoids. Maximal biomass productivity (over 2 g (dry weight) m−2 d−1 or 80 g m−3 d−1) was achieved at 38 cm s−1, flow rate; 2 × 109 cells l−1, initial population density; 25 °C, temperature; semi-continuous regime, keeping a cell density interval between 2 × 109 and over 4 × 109 cells l−1. Coverage of the tubular loop with a sunshade screen to avoid light-induced damage of cells was essential to maintain growth performance. The cellular β-carotene level increased significantly during the light period, as also did that of lutein. The rise in the β-carotene level could be accounted by the 9-cis-isomer, with all-trans-β-carotene remaining steady during the light period. By sunset, the ratio between 9-cis- and all-trans-isomers of β-carotene amounted to 1.5, with over 60% of total β-carotene corresponding to the 9-cis-isomer. Removal of sunshade enhanced carotenoid accumulation by cells to reach up to 10% of dry biomass. Cultivation of Dunaliella in closed tubular photobioreactor, thus represents a suitable approach for the production of a high-quality microalgal biomass enriched in the valuable 9-cis-isomer of β-carotene and lutein.