Effects of Light Intensity and the Remaining Nitrate Concentration on the Beta-Carotene Accumulation of a Wild Dunaliella salina Strain Isolated from the Saline Soil

An isolated Dunaliella salina strain from northern Thailand was cultured in modified Johnson’s medium in column photobioreactor. The beta-carotene accumulation mainly depended on the quantities of cells entering into carotenogenesis condition that was significantly enhanced by high started KNO₃ concentration. Low remaining nitrate concentration in the culture of each cell (RNCC) was suitable for algae to accumulate beta-carotene. Following the cultivation time extended, RNCC of all cultures decreased and tended to the same level (10–20 pg/cell) although the biomass or betacarotene content in the culture was higher in high started KNO₃ concentration. High light intensity restrained the growth especially in low KNO3 concentration but improved betacarotene accumulation and RNCC. The highest biomass and beta-carotene dry weight (DW) were 2.25 g L⁻¹ and 79.2 mg g⁻¹ DW respectively. Above results indicated that increasing the biomass and as early as possible to strengthen the stress on each cell was important to improve the final beta-carotene yield.