Redox potential in submerged citric acid fermentation

Turk Biyokimya Dergisi Turkish Journal of Biochemistry, 2010

Objective: Citric acid is mainly produced by submerged fermentation of Aspergillus niger. The process yield depends on the composition of the medium, as well as on the microorganism strain. Materials and Methods: In the present study citric acid production by Aspergillus niger M-101 using lower alcohols such as methanol and ethanol at concentration of 0.5 to 2.0 % (v/v) was optimized in shake flask culture using beet molasses as fermentation medium. Results: Methanol (1.5 %) and ethanol (1 %) was found optimal for maximum citric acid production (49.33±4.23 g/l) and (40.85±0.48 g/l) respectively. The effect of addition of ethanol and methanol to the fermentation medium at different time intervals on citric acid production demonstrate that maximum citric (44.62±2.12 g/l) and (55.13±1.53 g/l) was produced after 30 h and 45 h of incubation period. The yield for methanol and ethanol was 1.54 and 2.33 higher than the control experiment. Conclusion: From the present study it is concluded that both methanol and ethanol under optimized conditions increases the permeability of cell membrane of Aspergillus niger M-101 that result in accumulation of citric acid in fermentation medium. The kinetic assessments demonstrate that there was a significant enhancement (p ≤ 0.05) in citric acid production over the control fermentation medium. The best results for the production of citric acid were observed after 192 h of fermentation period.

Bioresource Technology, 1995

Experiments showed that kumara and taro were excellent substrates for citric acid production by solid-substrate fermentation using Aspergillus niger-Conversely, potato was a poor substrate, although it supported profuse fungal growth. A kinetic analysis of citrate production from kumara showed an overall reactor productivity of 0"48 g citrate/kg wet weight kumara per hour, with a yield of 0.54 on a weight basis (g citrate produced/g starch used). Maximum citrate production rates were observed after 2 to 3 days of fermentation, while the fungal growth rate was still high. The optimum moisture content of the kumara for citrate production was 65% (w/w) or above, while metal ions were shown not to be inhibitory to the process.

Two starchy substrates like pumpkin and cane molasses were selected for citric acid fermentation by using gamma ray induced mutant strains of 14/20 and 79/20 of A. niger under surface culture condition. Citric acid production was also different with various fermentation media by A. niger 14/20 and 79/20 strains. It was found to increase with the increase of fermentation period and maximum citric acid was found on day 13. In the presence of Prescott salt citric acid production was found lower than the absence of Prescott salt. Without Prescott salt highest values of citric acid production was found in mixed fermentation medium which were about 14.86 mg/ml and 14.44 mg/ml for A. niger 14/20 and 79/20 strains respectively, lowest production of citric acid was found in molasses medium for A. niger 14/20 and 79/20 strains were 7.72 and 7.57 mg/ml respectively. Whereas in the presence of Prescott salt, lowest production of citric acid in Pumpkin medium was found 2.86 mg/ml for A. niger 14/20 and 2.7 mg/ml for A. niger 79/20. Highest amount of citric acid was produced in molasses medium 4.88 mg/ml for A. niger 14/20 on day 13 with the presence of Prescott salt whereas 4.75 mg/ml for A. niger 79/20 strains respectively. Mixed substrate prepared with molasses and pumpkin media was proved to be the best and potential for citric acid production.

Two starchy substrates like pumpkin and cane molasses were selected for citric acid fermentation by using gamma ray induced mutant strains of 14/20 and 79/20 of A. niger under surface culture condition. Citric acid production was also different with various fermentation media by A. niger 14/20 and 79/20 strains. It was found to increase with the increase of fermentation period and maximum citric acid was found on day 13. In the presence of Prescott salt citric acid production was found lower than the absence of Prescott salt. Without Prescott salt highest values of citric acid production was found in mixed fermentation medium which were about 14.86 mg/ml and 14.44 mg/ml for A. niger 14/20 and 79/20 strains respectively, lowest production of citric acid was found in molasses medium for A. niger 14/20 and 79/20 strains were 7.72 and 7.57 mg/ml respectively. Whereas in the presence of Prescott salt, lowest production of citric acid in Pumpkin medium was found 2.86 mg/ml for A. niger 14/20 and 2.7 mg/ml for A. niger 79/20. Highest amount of citric acid was produced in molasses medium 4.88 mg/ml for A. niger 14/20 on day 13 with the presence of Prescott salt whereas 4.75 mg/ml for A. niger 79/20 strains respectively. Mixed substrate prepared with molasses and pumpkin media was proved to be the best and potential for citric acid production.

Under surface culture condition, a number of cheap indigenous raw materials like cane molasses and jackfruits were selected for citric acid fermentation and gamma ray induced mutant strains of 14/20 and 79/20 of Aspergillus niger were used. The rate of citric acid production was also influenced by biomass production and residual sugar used. In both cases on the day 13 without presence of Prescott salt for the mutant strain of Aspergillus niger 14/20 the citric acid production was highest. The biomass production was found different in various fermentation medium. It was found to increase with the increase of fermentation period and maximum biomass was found on day 13. It is also found that biomass production was higher in mutant strain of A. niger 14/20 than 79/20. In addition to this, wet-weight biomass was higher than dry weight biomass. Without presence of Prescott salt, wet weight of mycelial body of the fungus Aspergillus niger 14/20 was found highest on day 13 in mixed substrates which was 160.15. Mixed substrate prepared with molasses and jackfruit media was proved to be the best and potential for biomass production. Sugar utilization rate was also different in various media during citric acid production by A. niger 14/20 and 79/20. Prescott salt was also found to have remarkable effect on sugar utilization for citric acid production except on days 0, 3 and 5. In presence of Prescott salt, sugar utilization was lower than without presence of Prescott salt in the molasses, jackfruit and mixed fermentation media during production of citric acid. With the increase of fermentation period, sugar concentration in the medium was reduced and maximum reduction was found on day 13. Without presence of Prescott salt and in mixed fermentation medium the highest production of citric acid was found by further mutated Aspergillus niger 14/20 which was about 16.16mg/ml.

African Journal of Microbiology Research, 2009

Surface and submerged fermentation methods were used to produce citric acid by Aspergillus niger using chemically defined media or cane molasses. Fermentation process parameters were optimized in pilot scale tower and tray fermenters. Fermentation was running from 10-20 days with pH controlled at 3-6.5. Citric acid concentrations varied from 60-100 g/L depending on the strain used, the substrate, the fermentation system and the general conditions under which fermentation took place (initial sugar concentration, aeration rate, inoculum size, pH and temperature). Some essential criteria such as lower process sensitivity to short interruptions or breakdowns in aeration, expenses for equipment, consumption of electrical energy and higher yield and productivity, showed that surface fermentation is superior to submerged fermentation. However, the yield and productivity obtained in submerged fermentation using indigenous strains of fungi is not yet high enough for commercial production.

The production of citric acid from cane molasses by Aspergillus niger in submerged culture was investigated. Different factors were affected on the citric acid production and the results revealed that: The highest value of citric acid concentration 29.84 g/l was obtained with 1.5 g/l K4Fe(CN)6. Maximum productivity of citric acid was obtained with the treatment of cane molasses with 10 g/l ammonium oxalate. At 0.20 g/l MgSO4.7H2O, citric acid reached its maximum being 33.2 g/L. 5x106 spores/100 ml was the best inoculum volume and citric acid concentration was 32.88. Certain metal ions are known to be inhibitory and some of it have stimulatory effect of citric acid production. Zn++ was have an inhibitory effect but Ca++ was have the stimulatory effect and citric acid production was 18.44, 32.51 g/l respectively. In the absence of ethanol, citric acid reached its maximum being 33.61 g/l. The air supply resulted in improved citric acid concentration being 51.1 g/l after 8 days. Citric ...

Bioresource Technology, 2007

In this work, sequential optimization strategy, based on statistical designs, was employed to enhance the production of citric acid in submerged culture. For screening of fermentation medium composition significantly influencing citric acid production, the two-level Plackett-Burman design was used. Under our experimental conditions, beet molasses and corn steep liquor were found to be the major factors of the acid production. A near optimum medium formulation was obtained using this method with increased citric acid yield by five-folds. Response surface methodology (RSM) was adopted to acquire the best process conditions. In this respect, the three-level Box-Behnken design was applied. A polynomial model was created to correlate the relationship between the three variables (beet molasses, corn steep liquor and inoculum concentration) and citric acid yield. Estimated optimum composition for the production of citric acid is as follows pretreated beet molasses, 240.1 g/l; corn steep liquor, 10.5 g/l; and spores concentration, 10 8 spores/ml. The optimum citric acid yield was 87.81% which is 14 times than the basal medium. The five level central composite design was used for outlining the optimum values of the fermentation factors initial pH, aeration rate and temperature on citric acid production. Estimated optimum values for the production of citric acid are as follows initial pH 4.0; aeration rate, 6500 ml/min and fermentation temperature, 31.5°C.

2009

Citric acid production using Aspergillus niger NRRL 567 grown on peat moss has been optimized in a column bioreactor using a statistically based method. A 2 3 full factorial design with eight fermentation conditions was applied to evaluate significance on citric acid production and their interactions between variables, where the three independent variables evaluated were aeration rate, bed depth and temperature. Aeration rate and fermentation temperature were identified to be significant variables. Citric acid production markedly increases with aeration rate and fermentation temperature; however, the bed depth of solid substrate showed an insignificant effect on citric acid production. The optimum fermentation condition for citric acid production in a column bioreactor consisted of aeration rate of 0.84 vvm, bed depth of 22 cm and fermentation temperature of 32 o C. Under a given condition, a maximum citric acid production of 120.6 g/l was predicted and matched well with the experimental value of 123.9 g/kg.