Penicillium variabile P16 is characterized by the ability to release high levels of glucose oxidase when grown in glucose-rich media converting, at the same time, glucose into gluconic acid. This work reports on gluconic acid production by the above strain grown in bench-top reactor under different strategies, traditional batch and fed-batch processes; Na2CO3 was substituted for CaCO3 as the buffering agent in order to prevent calcium gluconate precipitation over the myceliurn that would limit oxygen uptake and, as a consequence, glucose conversion. Best results were obtained with an improved fed-batch process which, in addition to glucose, was continuously fed with nitrogen and minerals at a flow rate of 0.02 ml min(-1): yield and total productivity were 99.4% and 2.02 g h(-1), respectively, and remained constant till the end of the fermentation (240 h). (C) 2008 Elsevier Inc. All rights reserved.