Abstract:
This research studied the cultivating condition of diatom Thalassiosira sp. in flat-panel photobioreactor for fucoxanthin production. The reduction of nitrogen concentration to 75% of the amount in F/2 medium resulted in similar fucoxanthin content (3.718 ± 0.4138 mg/g) to the cultivation using the standard F/2 medium. Adjustment of incoming light intensity, in order to maintain relatively constant light intensity at the back-panel of the photobioreactor at 2000 lux, yielded the highest dried weight, maximum specific growth rate, biomass productivity and fucoxanthin productivity at 0.23 ± 0.001 g/L, 0.72 ± 0.008 day-1, 21.01 ± 0.454 mg/L·day and 0.048 ± 0.003 mg/L·day, respectively. The next experiment, involving adjustment of light quality (wavelength), indicated that the cultivation using blue light at 2000 lux was capable of enhancing fucoxanthin accumulation in biomass greater than white and red lights. The subsequently study demonstrated that the presence of carbon dioxide (2% v/v) did not improve biomass and fucoxanthin production and yielded similar growth performance as compared to the cultivation using ambient air, whereas the additional supply of macronutrients during the growth period could reduce growth limitation of diatoms. The final experiment combined the results of earlier cultivation (i.e., namely reduced nitrogen concentration to 75% of the amount in F/2 medium, maintaining the light intensity at the back-panel of the photobioreactor at 2000 lux during the growth period, illuminating with blue light during stationary phase, and supplying additional macronutrients). Under the described condition, biomass and fucoxanthin productivities were 45.18 ± 5.870 and 0.127 ± 0.0040 mg/L·day, respectively, which were approximately 154% and 28% higher than the normal cultivation using white light at 5000 lux.