Abstract
This study investigated the malic acid production capability of Aspergillus oryzae NRRL 3488 with three different CaCO3 concentrations, 20 g/L, 80 g/L, and 120 g/L, used as pH buffers and CO2 supply. A black box model was used to determine the distribution of metabolites throughout the fermentation. Comparing the malic acid production for the three different concentrations of CaCO3 after 240 h of fermentation, it was found that 300 % and 400 % more malic acid was produced in the 80 g/L and 120 g/L, in comparison to the 20 g/L experiment. Glucose consumption increased from 65 % for the 20 g/L CaCO3 to 91 % for the 80 g/L CaCO3, and 100 % consumption for the 120 g/L CaCO3 after 240 h. Total available nitrogen measurements indicated incomplete nitrogen consumption for all CaCO3 concentrations. Nitrogen conversions of 68 %, 78 %, and 81 % were measured for the 20 g/L, 80 g/L, and 120 g/L CaCO3. These results indicate that nitrogen limitation is not the determining factor for malic acid production. It is hypothesised that the malic acid production is facilitated by sufficient pH control as well as the availability of CO2. It is unclear whether oxygen limitation in the system is a requirement for malic acid production. Commercial malic acid production by A. oryzae NRRL 3448 would require a sufficient pH control and an abundant supply of CO2.
