Highly aerated cultures boost gluconic acid production by the yeast-like fungus Aureobasidium pullulans

Abstract

The ability of Aureobasidium pullulans NCYC 4012 to produce gluconic acid (GA) was firstly studied in flask batch cultures and it was found that GA productivity was not affected by initial glucose concentration, but highest substrate uptake rate was observed at glucose concentration of 80 g L−1. The effect of oxygen mass transfer, varied by changing agitation and aeration rates or total air pressure, was evaluated in batch cultures of A. pullulans in stirred tank bioreactors. Higher productivities were attained in conditions of high oxygen mass transfer and it was proven that the use of increased total pressure of 4 bar is an effective means of oxygen supply to A. pullulans cultures. At increased pressure, cells induced the antioxidant intracellular enzyme superoxide dismutase to cope with oxidative stress due to high oxygenation conditions. On the other hand, extracellular glucose oxidase activity was reduced by highly oxygenated conditions, suggesting opposite effects of oxygen on this enzyme secretion and GA production.