β-Carotene Production from <i>Dunaliella salina</i> Cultivated with Bicarbonate as Carbon Source

Abstract

Bicarbonate has been considered as a better approach for supplying CO₂ to microalgae cells microenvironments than gas bubbling owing t°Cost-effectiveness and easy operation. However, the β-carotene production was too low in <i>Dunaliella salina</i> cultivated with bicarbonate in previous studies. Also, the difference in photosynthetic efficiency between these tw°Carbon sources (bicarbonate and CO₂) has seldom been discussed. In this study, the culture conditions, including NaHCO₃, Ca²⁺, Mg²⁺ and microelement concentrations, were optimized when bicarbonate was used as carbon source. Under optimized condition, a maximum biomass concentration of 0.71 g/l and corresponding β-carotene content of 4.76% were obtained, with β-carotene yield of 32.0 mg/l, much higher than previous studies with NaHCO₃. Finally, these optimized conditions with bicarbonate were compared with CO₂ bubbling by online monitoring. There was a notable difference in <i>F_v/F_m</i> value between cultivations with bicarbonate and CO₂, but there was no difference in the <i>F_v/F_m</i> periodic changing patterns. This indicates that the high concentration of NaHCO₃ used in this study served as a stress factor for β-carotene accumulation, although high productivity of biomass was still obtained.