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

Bicarbonate has been considered as a better approach to supply CO2 to microalgae cells' microenvironment than gas bubbling owing to cost-effectiveness and easy operation. However, the beta-carotene production was too low in D. salina cultivated with bicarbonate in previous studies. Also, the difference on photosynthetic efficiency between these two carbon sources (bicarbonate and CO2) was seldom discussed. In this study, the culture conditions, including NaHCO3, Ca(2+), Mg(2+) and microelements' concentrations, were optimized when bicarbonate was used as carbon source. Under optimized condition, the maximum biomass concentration of 0.71 g.L(-1) and corresponding beta-carotene content of 4.76% was obtained, with beta-carotene yield of 32.0 mg.L(-1), much higher than previous studies with NaHCO3. Finally, this optimized conditions with bicarbonate were compared with CO2 bubbling by online monitoring. There is notable difference in Fv/Fm value between cultivations with bicarbonate and CO2, but there was no difference in the Fv/Fm periodic changing patterns. This indicates that high concentration of NaHCO3 used in this study played as a stress factor for beta-carotene accumulation, although high productivity of biomass still obtained.