ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Optimization of ammonium nitrate concentration in single-stage continuous cultures of Aspergillus niger with biomass retention

M. Janczar and J. J. Pietkiewicz

Food Biotechnology Department, Institute of Chemistry and Food Technology, Wroclaw University of Economics, PL-53 345 Wroclaw, Poland

E-mail: malgorzata.janczar@ae.wroc.pl

Received: 7 April 2006  Revised: 25 November 2006  Accepted: 28 November 2006

Abstract: The effect of ammonium nitrate concentration in the citric acid biosynthesis by Aspergillus niger NC-12 in single-stage continuous cultures with biomass retention was investigated. Experiments were carried out in a BIOMER laboratory fermenter with 5 dm³ working volume. At the initial stage of each cultivation, the substrate in the bioreactor contained 1.5 g NH₄NO₃ dm⁻³. After 120 h onwards, the bioreactor was fed continuously at a constant dilution rate of 0.009 h⁻¹. NH₄NO₃ concentration in the feed was varied from one culture to another, ranging between 0.5 g dm⁻³ and 2.5 g dm⁻³. Promising results were obtained when NH₄NO₃ concentration of 1.5 g dm⁻³ was used. The observed concentration of citric acid (c _P) and yield of citric acid with respect to the introduced sucrose (Y _P/S) were 117.88 g dm⁻³ and 78.59 %, respectively. The efficiency coefficient of citric acid biosynthesis (K _ef) was very high, amounting to 83.38.

Keywords: ammonium nitrate - Aspergillus niger - biomass retention - citric acid - continuous culture

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-007-0016-5

Chemical Papers 61 (3) 176–180 (2007)