Export of intracellular Monascus pigments by two-stage microbial fermentation in nonionic surfactant micelle aqueous solution.

Microbial fermentation of intracellular product is usually limited by high intracellular product concentration inhibition and complex downstream product processing. Perstractive fermentation of intracellular Monascus pigments in the nonionic surfactant Triton X-100 aqueous solution was studied in the present work, in which the intracellular product was exported from the intracellular to the extracellular aqueous solution and consecutively extracted into the nonionic surfactant micelles. After the second stage perstractive fermentation in the two-stage operation mode, biomass increased from 5 to 24 g/l DCW. The corresponding extracellular concentrations of yellow, orange, and red pigments were 60, 49 and 26 AU. The increase of cell density and the final pigment concentration were difficult to occur in a conventional aqueous medium using the two-stage fermentation. This positive effect of perstractive fermentation was ascribed to low intracellular pigment density, which eliminated the product inhibition and prevented the product from further degradation. The high efficiency of perstractive fermentation was further confirmed by fed-batch operation mode, in which the final biomass reached 28 g/l DCW and the corresponding extracellular concentrations of yellow, orange, and red pigments were 130, 84 and 47 AU.