High-content fructooligosaccharides production using two immobilized microorganisms in an internal-loop airlift bioreactor

Production of high-content fructooligosaccharides (FOSs) from sucrose using calcium alginate-immobilized mycelia of Aspergillus japonicus and Aspergillus niger in an internal-loop airlift bioreactor was investigated. The optimal entrapment of mycelia in A. japonicus and A. niger in calcium alginate were 1% and 7% (w/w), respectively. When 60 g of the immobilized mycelia of A. japonicus was supplied into the reactor filling with 3-L 300 g/L sucrose solution and gas velocity 7.32 cm/s, the total FOS production was about 55% (w/w) of total sugars in the mixture after a batch reaction for 9 h. To remove the generated glucose, an inhibitor of β-d-fructofuranosidase, the optimal input of the second immobilized A. niger mycelia particles was 315 g. With this input, the total FOSs mass fraction reached up to 90% (w/w) and the initial rate of transfructosylation was increased almost twice as without supplying glucose oxidase. In addition, 5.49 cm/s was suggested as the operating gas velocity for considering sufficient oxygen supply for glucose oxidase without generating excessive shear stress to damage the immobilized particles.