Determination of the maximum product yield from glucoamylase-producing Aspergillus niger grown in the recycling fermentor

Abstract

Aspergillus niger has been grown in glucose-and maltose-limited recycling cultures to determine the maximum growth yield, the maximum product yield for glucoamylase production, and the maintenance requirements at very slow specific growth rates. Using the linear equation for substrate utilization, and using the experimental data from both recycling experiments,both the maximum growth yield,Y_xsm,and the maximum product yield, Y_psm,could be determined. The values estimated were 157 g biomass per mol maltose for Y_xsmand 100 g protein per mol maltose for Y_psm. Expressed on a C₁-basis these values are 0.52 and 0.36 C-mole per C-mol for respectively Y_xsmand Y_psm The found value for Y_psmis half the value found for alkaline serine protease production in Bacillus licheniformis, and it can be concluded that formation of extracellular protein is more energy consuming in filamentous fungi than in prokaryotic organisms. Maintenance requirements are no significant factor during growth of Aspergillus niger, and reported maintenance requirements are most probably due to differentiation.