Production of ethanol directly from potato starch by mixed culture of Saccharomyces cerevisiae and Aspergillus niger using electrochemical bioreactor

When cultivated aerobically, Aspergillus niger hyphae produced extracellular glucoamylase, which catalyzes the saccharification of unliquified potato starch into glucose, but not when grown under anaerobic conditions. The Km and Vmax of the extracellular glucoamylase were 652.3 mg starch l-1 and 253.3 mg glucose l-1 min-1, respectively. In mixed culture of A. niger and Saccharomyces cerevisiae, oxygen had a negative influence on the alcohol fermentation of yeast, but activated fungal growth. Therefore, oxygen is a critical factor for ethanol production in the mixed culture, and its generation through electrolysis of water in an electrochemical bioreactor needs to be optimized for ethanol production from starch by coculture of fungal hyphae and yeast cells. By applying pulsed electric fields (PEF) into the electrochemical bioreactor, ethanol production from starch improved significantly: Ethanol produced from 50 g potato starch l-1 by a mixed culture of A. niger and S. cerevisiae was about 5 g l-1 in a conventional bioreactor, but was 9 g l-1 in 5 volts of PEF and about 19 g l-1 in 4 volts of PEF for 5 days.