Improvement on citric acid production in solid-state fermentation by Aspergillus niger LPB BC mutant using citric pulp

Abstract

Citric acid (CA) production has been conducted through a careful strain selection, physical–chemical optimization and mutation. The aim of this work was to optimize the physical–chemical conditions of CA production by solid-state fermentation (SSF) using theAspergillus niger LPB BC strain, which was isolated in our laboratory. The parental and mutant strain showed a good production of CA using citric pulp (CP) as a substrate. The physical– chemical parameters were optimized and the best production was reached at 65% moisture, 30 °C and pH 5.5. The influence of the addition of commercial and alternative sugars, nitrogen sources, salts, and alcohols was also studied. The best results (445.4 g of CA/kg of CP) were obtained with sugarcane molasses and 4% methanol(v/w). The mutagenesis induction of LPB BC was performed with UV irradiation. Eleven mutant strains were tested in SSF where two mutants showed a higher CA production when compared to the parental strain. A. niger LPB B3 produced 537.6 g of CA/kg of CP on the sixth day of fermentation, while A.niger LPB B6 produced 616.5 g of CA/kg of CP on the fourth day of fermentation, representing a 19.5% and 37% gain, respectively.