The Optimum use of Salinity, Nitrate and Pond Depth for β-Carotene Production of Dunaliella salina

Abstract

Dunaliella salina, halotorelant green algae was collected from the East Coast of Thailand. It has a massive accumulation of β-carotene when grown under defined growth conditions such as high light intensity, high salt concentration and nitrate deficiency. The present study investigated the optimization of salinity, nitrate and pond depth for cell growth and β-carotene production of the alga in question. Cultivation was done in three stages. These were indoor cell growth cultivation, outdoor cell growth cultivation and outdoor β-carotene production. The optimum salinity for cell growth of indoor and outdoor cultivation (5 l) was 9% NaCl, which has specific growth rate (µ) of 0.579 (d^-1) and 0.981 (d^-1). The optimum salinity for outdoors β-carotene production (5 l) when use 40% inoculum (2.16 x 10⁶ cell ml^-1) was 12% NaCl. This produced b-carotene content of 51.73             µg ml^-1. In addition, the concentrations of medium used were 100%, 75% and 50% to decrease nitrate concentration in the starter ponds for
increasing β-carotene production in the next step. The results showed that 50% medium gave minimum nitrate concentration of 4.5 mg l^-1. For the effect of pond depth, the light expose of the alga were used 9, 11, 13 and 18 cm the ratios of carotenoid to chlorophyll were 7.48, 6.25, 5.54 and 3.35, respectively. Therefore the suitable pond depth for β-carotene production from D. salina was 9 to 11 cm.