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

Abstract

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 2g (dry weight) m(-2) d(-1) or 80 gm(-3) d(-1)) was achieved at 38 cm s(-1), flow rate; 2 x 10(9) cells l(-1), initial population density; 25 degrees C, temperature; semi-continuous regime, keeping a cell density interval between 2 x 10(9) and over 4 x 10(9) 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 beta-carotene level increased significantly during the light period, as also did that of lutein. The rise in the beta-carotene level could be accounted by the 9-cis-isomer, with all-trans-beta-carotene remaining steady during the light period. By sunset, the ratio between 9-cis- and all-trans-isomers of beta-carotene amounted to 1.5, with over 60% of total beta-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 beta-carotene and lutein.