Optimization And Scale-up Of Glucoamylase Fermentation Process Using Black Box Model By Aspergillus Niger

Glucoamylase is secreted by Aspergillus niger with exonuclease activity of extracelluar enzymes. The main role of glucoamylase is hydrolysis of polysaccharides such as starch to release β-D-glucose. Glucoamylase is widely used in food,pharmaceutical, fermentation and other industries. Due to its effective protein secretion capabilities, Aspergillus niger is an excellent producer of glucoamylase and the yield of glucoamylase can reach 20 g/L. In order to further improve the production of glucoamylase, the design and optimization of the fermentation process is essential for improving the production of glucoamylase.Constructing the kinetic model is centrally important to the design and optmization of the fermentation process. Carbon-limited continuous culture was used to study the relationship between the growth of Aspergillus niger and the production of glucoamylase in this paper. The result showed that the production of glucoamylase was partially growth-associated and fitted the Luedeking-Piret equation well. Combined with the Monod dynamics model of glucose consumption of Aspergillus niger and the Herbert-Pirt equation of glucose and oxygen consumption, the black-box model of Aspergillus niger for glucoamylase production was built up.The validation of the black-box model was made in fed-batch culture. The fed-batch culture with exponential and constant feed rate were designed, respectively. The results showed that the black-box model could successfully describe the glucose consumption biomass production, glucoamylase production and oxygen consumption under the exponential fed-batch culture (pseudo steady state), but it was not applicable to the fed-batch culture with constant feed rate.Considering the black-box kinetic model could stuitably describe the exponential fed-batch culture, the scale-up of glucoamylase using Aspergillus niger was conducted based on the black-box model on 500 L fermenter scale. The prediction result showed that the model could describe the glucose consumption, biomass procduction and oxygen consumption well, but the glucoamylase production was only half of the model predicted, compared with the fermentation result in 5 L, more glucose consumption was used to the maintenance metabolism and production of carbon dioxide. In addition, influences of different impeller combination (the combination of RT and HBT and the combination of WHu) on Aspergillus niger were studied in 500 L-scale bioreactor, the result showed that was the production of glucoamylase improved 7% with the combination of WHu, the percentage of oxalate in product increased and the percentage of canbon dioxide decreased significantly. The reason was using the combination of WHu improved the mixing and increased the consistency of the physiological metabolism of Aspergillus niger.