Optimization of citric acid production from glucose by Yarrowia lipolytica

Abstract

Citric acid (CA) is mainly produced in a biotechnological process using Aspergillus niger. In this process, large amounts of wastes have to be removed. Since the use of Yarrowia lipolytica for CA production is an environmental compatible alternative method, the CA production was optimized in regard to growth temperature and pH as well as substrate and product inhibition. The highest value of the maximum specific growth rate at pH 6.5 was found to be μmax = 0.192 h-1, whereas the largest amount of CA of 24.91 g/L as well as the highest selectivity of the bioprocess (89.9% CA) and the maximum yield (0.22 gCA/gGlucose) were obtained at pH 6.0. During the growth phase, the temperature optimum was found to be in the range of 30-34°C (μmax = 0.132 h-1). Nevertheless, the highest concentration of CA during the production phase was obtained at 30°C (41 g/L CA, 93.1 % CA, 0.55 gCA/gglucose). In studying the substrate inhibition of the process, a clear tendency of decrease in the maximum specific growth rate was detected when the initial glucose concentration was increased from 50 g/L (μmax = 0.17 h-1) to 200 g/L (μmax = 0.055 h-1). The addition of 120 g/L CA to the culture broth at the start of the production phase reduced the production of CA from 32.1 g/L to 7.4 g/L. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.