β-Carotene Production from Dunaliella salina Cultivated with Bicarbonate as Carbon Source

Bicarbonate has been considered as a better approach for supplying CO(2) to microalgae cells microenvironments than gas bubbling owing to cost-effectiveness and easy operation. However, the β-carotene production was too low in Dunaliella salina cultivated with bicarbonate in previous studies. Also, the difference in photosynthetic efficiency between these two carbon sources (bicarbonate and CO(2)) has seldom been discussed. In this study, the culture conditions, including NaHCO(3), Ca(2+), Mg(2+) and microelement concentrations, were optimized when bicarbonate was used as carbon source. Under optimized condition, a maximum biomass concentration of 0.71 g/l(-1) and corresponding β-carotene content of 4.76% were obtained, with β-carotene yield of 32.0 mg/l(-1), much higher than previous studies with NaHCO(3). Finally, these optimized conditions with bicarbonate were compared with CO(2) bubbling by online monitoring. There was a notable difference in F(v)/F(m) value between cultivations with bicarbonate and CO(2), but there was no difference in the F(v)/F(m) periodic changing patterns. This indicates that the high concentration of NaHCO(3) used in this study served as a stress factor for β- carotene accumulation, although high productivity of biomass was still obtained.