Extractive Fermentation for Production of Lactic Acid from Corn Starch by Filamentous Fungi Immobilized in Fibrous Bed Bioreactor

Lactic acid fermentations have been extensively studied in the past decade. Almost all previous studies and current commercial processes use glucose or lactose and very little has been done with starch as the substrate for fermentation. There is a cost advantage in using starch, instead of glucose, for fermentation. The goal of this project is to develop a novel fungal extractive fermentation process to economically produce L(+)-lactic acid from corn meal (starch) generated in a corn dry-milling process. Several new approaches to enhance lactic acid yield and productivity from direct fungal fermentation of starch will be studied in this project. First, immobilization of the mycelial cells in a porous fibrous matrix to control cell morphology and to enhance mass transfer, viable cell density, and reaction rate will be studied. Using immobilized cells with reduced or minimal growth activity should also enhance the lactic acid yield as less carbon source will be used for cell biomass and ATP formation. Second, extractive fermentation to separate lactic acid in situ to reduce product inhibition and to further enhance the fermentation rate will be studied. Lactic acid in the fermentation broth will be separated by solvent extraction in hollow-fiber membrane extractors. It is believed that by selectively removing lactic acid from the fermentation broth continuously, the fermentation pathway can be shifted to produce more lactic acid and less other byproducts.