solid state fermentation

Kumar et al. (2003) used solid state fermentation (SSF) method to produce citric acid by Aspergillus niger DS 1 using sugarcane bagasse as a carrier and sucrose or molasses based medium as a moistening agent. Initially bagasse and wheat bran were compared as carrier. Bagasse was the most suitable carrier, as it did not show agglomeration after moistening with medium, resulting in better heat and mass transfer during fermentation and higher product yield. Different parameters such as moisture content, particle size, sugar level and methanol concentration of the medium were optimised and 75% moisture level, 31.8 g sugar/100 g dry solid, 4% (v/w) methanol and particles of the size between 1.2 and 1.6 mm were found to be optimal. Sucrose and clarified and non-clarified molasses medium were also tested as moistening agents for SSF and under optimised conditions, 20.2, 19.8 and 17.9 g citric acid /100 g of dry solid with yield of 69.6, 64.5 and 62.4% (based on sugar consumed) was obtained in sucrose, clarified and non-clarified molasses medium respectively, after 9 days of fermentation.

Rodriguez and Sanroman (2004) invested that Solid-sate fermentation (SSF) has received new interest not only from researchers but also from industry. This technique has become a very attractive and alternative to submerged (SmF) for specific application due to the recent improvements in reactor designs

Vandenberghe et al. (2004) studied were conducted to evaluate citric acid production by solid-state fermentation (SSF) using cassava bagasse as substrate employing a fungal culture of Aspergillus niger LPB 21 at laboratory and semipilot scale. Optimization of the process parameters temperature, pH, initial humidity, aeration, and nutritive composition was conducted in flasks and column fermentors. The results showed that thermal treatment of cassava bagasse enhanced fungal fermentation efficacy, resulting in 220 g of citric acid/kg of dry cassava bagasse with only treated cassava bagasse as substrate. The results obtained from the factorial experimental design in a column bioreactor showed that an aeration rate of 60 mL/min (3 mL/[g.min]) and 60% initial humidity were optimum, resulting in 265.7 g/kg of dry cassava bagasse citric acid production. This was almost 1.6 times higher than the quantities produced under unoptimized conditions (167.4 g of citric acid/kg of dry cassava bagasse). The defined parameters were transferred to semipilot scale, which showed high promise for large-scale citric acid production by SSF with cassava bagasse. Respirometry assays were carried out in order to follow indirectly the biomass evolution of the process. Citric acid production reached 220, 309, 263, and 269 g/kg of dry cassava bagasse in Erlenmeyer flasks, column fermentors, a tray bioreactor, and a horizontal drum bioreactor, respectively.

Ikram et al. (2004) investigated deals with citric acid production by some selected mutant strains of Aspergillus niger from cane molasses in 250 ml Erlenmeyer flasks. For this purpose, a conidial suspension of A. niger GCB-75, which produced 31.1 g/l citric acid from 15% (w/v) molasses sugar, was subjected to UV-induced mutagenesis. Among the 3 variants, GCM-45 was found to be a better producer of citric acid (50.0 +/- 2a) and it was further improved by chemical mutagenesis using N-methyl, N-nitro-N-nitroso-guanidine (MNNG). Out of 3,2-deoxy-D-glucose resistant variants, GCMC-7 was selected as the best mutant, which produced 96.1 +/- 1.5 g/l citric acid 168 h after fermentation of potassium ferrocyanide and H2SO4 pre-treated blackstrap molasses in Vogel's medium. On the basis of kinetic parameters such as volumetric substrate uptake rate (Qs), and specific substrate uptake rate (qs), the volumetric productivity, theoretical yield and specific product formation rate, it was observed that the mutants were faster growing organisms and produced more citric acid. The mutant GCMC-7 has greater commercial potential than the parental strain with regard to citrate synthase activity. The addition of 2.0 x 10-5 M MgSO4x5H2O into the fermentation medium reduced the Fe2+ ion concentration by counter-acting its deleterious effect on mycelial growth. The magnesium ions also induced a loose-pelleted form of growth (0.6 mm, diameter), reduced the biomass concentration (12.5 g/l) and increased the volumetric productivity of citric acid monohydrate (113.6±5 g/l).

Gokhan et al. (2005) The production of citric acid was achieved by using Aspergillus niger conidiaspores, entrapped in Ca-alginate beads, and the factors that affect this production were investigated. The effects of starting sucrose concentration (100-180 g/l), nitrogen concentration (0-0.3 g/l), methanol concentration (0-6 ml) and finally ethanol concentration (0-5 ml) in 100 ml feeding medium on citric acid production were studied and optimum experimental conditions were determined. The starting nitrogen concentration (0.05 g/l) and the starting sucrose concentration (140 g/1) were optimized and maximum citric acid production observed under these given conditions. Maximum citric acid production was observed upon addition of 4.0 ml methanol and 3.0 ml ethanol.