Production and biotransformation of 6-pentyl-alpha-pyrone by Trichoderma harzianum in two-phase culture systems.

The final concentration of 6-pentyl-a-pyrone (6PP) produced in cultures of Trichoderma spp. is limited by the fact that inhibition of biomass growth occurs at 6PP concentrations as low as 100 mg/l. The aim of this work was to evaluate liquid-liquid extractive fermentation systems as an alternative to overcome the toxicity problems and to increase the production of 6PP by this fungus. Two alkanes (n-decane and n-hexadecane) and two dicarboxylic esters (dibutyl phthalate and dioctyl phthalate) were evaluated in shake flask cultures. The highest 6PP production (173 ppm) was achieved when n-hexadecane was used, being 3.5-fold the maximum 6PP concentration of a culture without the solvent. Cultivation of Trichoderma harzianum in a 10-1 bioreactor with n-hexadecane yielded 6PP production ninefold higher than that from control cultures. However, 6PP production in the bioreactor (83 ppm) was lower than in shake flasks. Differences in the power drawn to the fluid at each scale could account for such behavior. Even in the presence of the solvent, 6PP content decreased after reaching its maximal concentration.