Effect of phosphorus and sodium chloride levels on growth performance, carotenoid accumulation and isomerization to 9-cis β-carotene in Thai Dunaliella salina NUAC09

Dunaliella is known as a commercial of β-carotene-producing microalgae. D. salina NUAC09 was previously isolated, and its characterization and beta-carotene-producing efficacy were investigated for further application. This study aimed to examine the effect of phosphorus (0, 0.043, 0.053 and 0.07 g KH2PO4/L) and sodium chloride (0.5, 1, 1.5, 2 and 2.5 M NaCl) on growth performance, accumulations of pigments, antioxidant activity and cis, trans β-carotene isomers ratio of Thai D. salina NUAC09. The strain NUAC09 was done using morphological investigation and phylogenetic analyses based on Internal Transcribed Spacer (ITS) sequences. Morphological features and the ITS phylogenetic trees revealed that the NUAC09 could be identified as D. salina. The strain NUAC09 was then separately grown under various phosphorus and NaCl levels as described above. Results showed that maximum cell density, chlorophyll a content, total carotenoid content, and biomass dry weight was observed in cells grown under 0.07 g KH2PO4/L and 2.5 M NaCl. HPLC analysis revealed that two β-carotene isomers, all-trans and 9-cis β-carotene were detected at 20.8 and 21.4 min retention time, respectively. The maximum all-trans β-carotene (178, 238 mg/g DW) and 9-cis β-carotene (99, 156 mg/g DW) content and the highest antioxidant activities (72.4 and 74.6 % inhibition) were observed in the absence of phosphorus (0 g KH2PO4/L) and 0.5 M NaCl, respectively. Overall, our results indicate that phosphorus and NaCl levels affect the growth, total carotenoid, antioxidant activity and β-carotene isomer content of NUAC09, suggesting a strategy to boost 9-cis isomer production by adjusting the nutrients in the growth medium.