Co-production of Gluconic Acid and Fructo-oligosaccharides by Aureobasidium pullulans from Sugarcane Molasses: Effect of Oxygen Transfer Rate in Stirred Tank and Airlift Bioreactors

Aureobasidium pullulans NCYC 4012 was used to produce gluconic acid (GA) and fructo-oligosaccharides (FOS) from sugarcane molasses (ScM). For the first time, three types of bioreactors operating at different conditions of oxygenation—a stirred tank reactor (STR) operating under atmospheric pressure varying stirring rate, a pressurized STR under increased air pressure up to 4 bar of air, and an airlift reactor under atmospheric pressure varying aeration rate—were employed for GA and FOS biosynthesis by A. pullulans. The highest oxygenation conditions favored GA production in the three bioreactors, whereas the synthesis of FOS was not favored by high oxygen availability. GA yields close to 1 g·g−1 (grams of GA produced per grams of glucose consumed) were achieved in bioreactors under atmospheric pressure, and the highest titer of GA of 75 g·L−1 was obtained in the airlift bioreactor. In this last, the highest concentration of total FOS of 65 g·L−1 and yield of FOS of 0.58 g·g−1 were obtained.