pH control strategy in astaxanthin fermentation bioprocess by Xanthophyllomyces dendrorhous

The effects of initial culture pH ranging from 3.5 to 6.5 on biomass content and astaxanthin concentration by Xanthophyllomyces dendrorhous were investigated in shake flask fermentation. An optimal initial pH of 6.0 for cell growth was obtained with cell density at 17.21 g/l, while an optimum pH of 5.0 for astaxanthin accumulation was obtained with volumetric concentration of astaxanthin at 20.48 mg/l. Batch bioprocess of astaxanthin fermentation by X. dendrorhous at various pH values ranging from 4.0 to 6.0 was examined. In batch fermentation under a controlled pH, the optimum pH for cell growth was 6.0 with specific cell growth 0.049 h(-1), and the optimum pH for astaxanthin formation in cell was 4.0 with specific product yield (Y-p/x) at 1.52 mg/g. A pH-shift strategy was developed to gain higher volumetric concentration of astaxanthin in batch fermentation. The maximum volumetric concentration of astaxanthin reached 27.05 mg/l, increased by 24.1% as comparison with that of constant pH fermentation. (c) 2005 Elsevier Inc. All rights reserved.