Mass production of C₅₀ carotenoids by Haloferax mediterranei in using extruded rice bran and starch under optimal conductivity of brined medium

Abstract

Microbial carotenoids have potentially healthcare or medical applications. Haloferax mediterranei was difficult to economically grow into a large quantities as well as producing a valuable pigment of carotenoids. This study reports a novel investigation into the optimal conductivity on the mass production of carotenoids from H. mediterranei. The major component at about 52.4 % in the extracted red pigment has been confirmed as bacterioruberin, a C₅₀ carotenoids, by liquid chromatography separation and mass spectrometry analysis. By maintaining higher conductivity of 40 S/m in the brined medium, the cell concentration attained to 7.73 × 10⁹ cells/L with low pigments concentration of 125 mg/L. When the conductivity was controlled at about 30 S/m, we obtained the highest cell concentration to 1.29 × 10¹⁰ cells/L with pigments of 361.4 mg/L. When the conductivity was maintained at optimal 25 S/m, the pigments can be increased to maximum value of 555.6 mg/L at lower cell concentration of 9.22 × 10⁹ cells/L. But conductivity below 20 S/m will cause the significant decrease in cell concentration as well as pigments due to the osmotic stress around the cells. Red pigment of carotenoids from an extremely halophilic archaebacterium could be efficiently produced to a high concentration by applying optimal conductivity control in the brined medium with extruded low-cost rice bran and corn starch.