Controlling filamentous fungal morphology by immobilization on a rotating fibrous matrix to enhance oxygen transfer and L(+)-lactic acid production by Rhizopus oryzae

Filamentous fungi are widely used in industrial fermentations. However, the filamentous morphology is usually difficult to control and often cause problems in conventional submerged fermentations. The fungal morphology has profound effects on mass transfer, cell growth, and metabolite production. Controlling the filamentous morphology by immobilization on a rotating fibrous matrix was studied for its effects on oxygen transfer and lactic acid production in aerobic fermentation by Rhizopus oryzae. Compared to the conventional stirred tank fermentor, the fermentation carried out in the rotating fibrous bed bioreactor (RFBB) resulted in a good control of the filamentous morphology, and improved oxygen transfer and lactic acid production from glucose. A high lactic acid concentration of 137 g/L with a high yield of 0.83 g/g and reactor productivity of 2.1 g/L(.)h was obtained with the RFBB in repeated batch fermentations. The process was stable and can be used for an extended operation period.