Dihydroxyacetone production from glycerol using Gluconobacter oxydans: Study of medium composition and operational conditions in shaken flasks.

The production of dihydroxyacetone from glycerol employing aerobic cultures of Gluconobacter oxydans is studied. Dihydroxyacetone is one of the most important value-added products obtained from glycerol, a by-product of biodiesel production. The effect of organic nitrogen source and initial substrate concentrations has been studied together with the possibility of product inhibition. Afterward, the influence of the main operating conditions (temperature, shaking speed, and initial biomass concentration) on in vivo glycerol dehydrogenase activity has also been considered. The results show no evidence of glycerol inhibition, but an important product inhibition was detected, which has been taken into account in a kinetic model for enzymatic activity description. In terms of operating conditions, pH was found to exert a great impact on glycerol conversion, being necessary to keep it above 4 to ensure complete glycerol conversion. The minimum temperature that maximized enzymatic activity was found to be 30°C. In addition, a surprising decoupling between biomass concentration and dihydroxyacetone production rate was observed when adding increasing nitrogen source concentrations at a fixed shaking speed. Glycerol dehydrogenase activity remains constant despite the increase in biomass concentration, contrary to what would be expected. This fact revealed the existence of a rate limiting factor, identified subsequently as oxygen transfer rate depending on the biomass concentration.