Modulated gluconic acid production from immobilized cells of Aspergillus niger ORS-4.410 utilizing grape must

Background: Gluconic acid (GA) production by immobilized cells of mutant Aspergillus niger ORS-4.410 on polyurethane sponge (PUS) and calcium-alginate (Ca-alginate) was evaluated in repeated batches of solid state surface fermentation (SSF) and submerged fermentation (SmF) conditions, respectively, utilizing rectified grape must as carbon source. Results: The passive immobilization of cells in fermentation medium solid support of having 0.4 cm³ cube size, 4% spore suspension, 0.6g inoculum of PUS immobilized cells at 32 °C and 2.0 L min^-1 resulted in the maximum GA production (88.16gL^-1) with a 92.8% yield, while the Ca-alginate matrix with a 0.5 cm diameter bead size, 2-3% spore suspension, 15g inoculum at 34 °C and 150 rpm agitation speed revealed 67.19gL^-1 GA with a 85.2% yield. Repeated use of PUS showed higher levels of GA (110.94gL^-1) in the third-fourth fermentation cycles with 95-98% yield and 22.50gL^-l d^-l productivity under SSF that was 2.S-fold higher than the productivity obtained from a typical fermentation cycle, and 54% greater than the productivity obtained with repetitive use of Ca-alginate immobilized cells of A. niger under SmF. Conclusion: Using immobilized cells of A. niger in PUS,the rectified form of grape must can be utilized for GA production as an alternative source of carbohydrate by replacing the conventional fermentation conditions.