Effect of light intensity on Beta-carotene production and extraction by Dunaliella salina in two-phase bioreactors

Application of two-phase bioreactors is a useful technique for improvement of the productivity of fermentations. Fermentative extraction of the products in situ is performed in this technique. The effect of light intensity on the extraction of ß-carotene from Dunaliella salina, in the fermentative extraction, has been investigated. Three different average light exposures were applied: 1.5×10-8 (low), 2.7×10-8 (intermediate) and 4.5×10-8 (high) µmol s-1 per cell. Results show that ß-carotene content of the cells increases by increasing the light exposure. Increase in the ß-carotene content of the cells is not necessarily coupled with an increase in the volumetric production of ß-carotene. Final volumetric production is about the same for the three bioreactors. ß-Carotene extraction rate is enhanced by the increase in the light exposure. The results suggest that extraction rate is related to ß-carotene content of the cells and is not essentially related to the volumetric production of ß-carotene. Although the effectiveness of extraction with respect to the light input is comparable for all light intensities applied, increasing the light input per cell leads to a higher volumetric extraction rate. Moreover, extracted ß-carotene stays very pure even so the extraction increased by the increase of light intensity.