solid state fermentation method

Pazouki and Panda (2002) studies have been considered very important in fungal fermentation. Morphological parameters and the type of mycelia present (free mycelia without any branches, branched mycelia and branched mycelia with conidiophore) were measured to correlate citric acid production with the morphology of Aspergillus niger. We observed that morphological parameters and the type of mycelia present varied with substrate concentration. They also depended on the type of substrate (molasses and glucose) used. Maximum citric acid (6.8 kg/m3) was produced when branched mycelia with conidiophore were the most available mycelia present in the broth of molasses containing medium. Citric acid was produced in lesser quantity (1.82 kg/m3) when glucose was used. The addition of methanol doubled citric acid production, increased slightly the percentage of branched mycelia with conidiophore and conditioned the surface of the mycelia.

Hang and Woodams (2002) investigated Corn husks could serve as a potential substrate for the production of citric acid by Aspergillus niger NRRL 2001. Combined treatments of corn husks with dilute NaOH and Rapidase Pomaliq (a commercial apple juice processing enzyme preparation) significantly enhanced the yield of citric acid. Under favorable conditions (pretreated with 0.5 mol/L NaOH, followed by 120 h of fermentation at 30°C in the presence of Rapidase Pomaliq), the yield of citric acid was 259±10 g per kg of dry matter of corn husks.

Pazouk et al. (2002) morphological studies have been considered very important in fungal fermentation. Morphological parameters and the type of mycelia present (free mycelia without any branches, branched mycelia and branched mycelia with conidiophore) were measured to correlate citric acid production with the morphology of Aspergillus niger. We observed that morphological parameters and the type of mycelia present varied with substrate concentration. They also depended on the type of substrate (molasses and glucose) used. Maximum citric acid (6.8 kg/m3) was produced when branched mycelia with conidiophore were the most available mycelia present in the broth of molasses containing medium. Citric acid was produced in lesser quantity (1.82 kg/m3) when glucose was used. The addition of methanol doubled citric acid production, increased slightly the percentage of branched mycelia with conidiophore and conditioned the surface of the mycelia.

Haq et al. (2003) study describes citric acid fermentation by Aspergillus niger GCB-47 in a 15-1 stainless steel stirred fermentor. Among the alcohols tested as stimulating agents, 1.0% (v/v) methanol was found to give maximum amount of anhydrous citric acid (90.02±2.2 g/l), 24 h after inoculation. This yield of citric acid was 1.96 fold higher than the control. Methanol has a direct effect on mycelial morphology and it promotes pellet formation. It also increases the cell membrane permeability to provoke more citric acid excretion from the mycelial cells. The sugar consumed and % citric acid was 108±3.8 g/l and 80.39±4.5%, respectively. The desirable mycelial morphology was in the form of small round pellets having dry cell mass 14.5±0.8 g/l. Addition of ethanol, however, did not found to enhance citric acid production, significantly. The maximum value of Yp/x (i.e., 5.825±0.25 g/g) was observed when methanol was used as a stimulating agent. The best results of anhydrous citric acid were observed, 6 days after inoculation when the initial pH of fermentation medium was kept at 6.0.

Kumar et al (2003) studied a solid state fermentation method was used to utilize pineapple, mixed fruit and maosmi waste as substrates for citric acid production using Aspergillus niger DS 1. Experiments were carried out in the presence and absence of methanol at different moisture levels. In the absence of methanol the maximum citric acid was obtained at 60% moisture level whereas in the presence of methanol the maximum citric acid was obtained at 70% moisture level. The stimulating effect of methanol was less at lower moisture level. The inhibitory effect of metal ions was also not observed and maximum citric acid yield of 51.4, 46.5 and 50% (based on sugar consumed) was obtained from pineapple, mixed fruit and maosmi residues, respectively.