Optimum conditions for citric acid production from local Aspergillus niger S11 isolate by submerged fermentation
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Aspergillus niger
Different strains of A. niger were used to examine their ability to produce citric acid and the results revealed that most of the nine tested strains were able to produce citric acid. A. niger CA2 was the highest producer strain during the fermentation on medium No. 2, while highest biomass weight was obtained during the growth of A. niger CA2 on medium No.1. But, highest value of consumption of sugars was found during the growth of A. niger NRRL 2270 on medium No.5. Highest value of conversion coefficient and the citric acid yield were obtained during the growth of A. niger CA2 on medium No. 2. Maximum production of citric acid was obtained after 8 days of fermentation and pH 5.5. At the same time, highest value of biomass, conversion coefficient and total sugars consumed were obtained at these conditions. At 15% sugars concentration, citric acid reached its maximum being 29.3 g/L. Maximum production (32.03 g/L) of citric acid was obtained with 2.0 g/L ammonium phosphate, also, give highest amount of biomass and citric acid yield. Highest value of citric acid concentration (32.88 g/L) and citric acid yield (21.92%) were obtained with 0.3 ml/L of phosphoric acid which was found as the best phosphorus source.
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The study involved the screening of fourteen isolates of Aspergillus niger for citric acid production from glucose. The study was aimed at screening and improving local strains of Aspergillus niger with potential for citric acid production. All the isolates screened produced varying amounts of citric acid, the highest was by the isolate designated CP3 which produced 12.81g/l and the least was B11 and O12 which produced 3.42g/l all after 6 days of submerged fermentation. The isolate CP3 was chosen for further studies. Strain improvement studies which was based on exposure of CP3 to ultraviolet irradiation for 10, 30 and 45 minutes increased citric acid yield to 22.20g/l (48.89% increase) by mutant M45 followed by a citric acid yield of 16.22g/l by the 30 minutes mutant (M30) and the least being M10 which produced 13.66g/l in all cases after 6 days of fermentation. The mutant (M45) also yielded higher amount of citric acid (19.64g/l) without methanol as additive compared to the parent strain (CP3) which gave a citric acid of 14.94g/l with the addition of methanol after six days (144h) of fermentation in both cases. Finding from this study showed that all the isolates have potential for citric acid production.Keywords: Isolation, Screening, Improvement, Aspergillus niger, Citric acid
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3 Abstract: 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.
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4 Abstract: Aspergillus niger is most commonly known among the various fungal strains screened for citric acid production, when cultivated in carbohydrate-rich medium of fermentation. In the present study, a number of indigenous raw materials such as molasses and jackfruits have been used for citric acid production. The previously isolated gamma-ray induced second step mutants 14/20 and 79/20 of A. niger were reradiated by Co 60 Gamma beam-650 source at a dose rate of 0.674 kGy/hr aiming to further increase the production of citric acid. In absence of Prescott salt and in mixed fermentation medium the highest production of citric acid was found by further mutated. A. niger 14/20 with gamma radiation at 20 Krad which was about 16.16 mg/ml and lowest citric acid production was found in molasses media by further mutated A. niger 14/20 with gamma radiation at 10Krad which was found 9.22 mg/ml on the day 13 but it was higher than that produced by the un irradiated strain. In absence of Prescott salt highest production of citric acid was found by further mutated A. niger 79/20 with gamma radiation at 20 Krad in mixed fermentation medium which was about 15.94 mg/ml. Lowest citric acid production was found in molasses media by further mutated A. niger 79/20 with gamma radiation at 10 Krad which was found 9.08 mg/ml on the day 13 but it was higher than that produced by the un irradiated strains.
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The ability of Aspergillus niger to produce citric acid from dates was evaluated. Two strains of A. niger (ATCC 6275 and 9642) were grown in media containing different concentrations of date extract or molasses fortified with whey, methanol and tricalcium phosphate. The fermentation experiments were conducted at 25° C for 12 days and samples were withdrawn at different time intervals and analyzed for their citric acid content. Results showed that a high level of citric acid (32.4gL−1) was produced by A. niger ATCC 6275 in 20% molasses in whey. When methanol and tricalcium phosphate were added, a significant increase in citric acid production was recorded (P < 0.05). Citric acid concentrations were 38.4 and 42.4 gL−1, in media fortified with methanol and tricalcium phosphate, respectively. Our results showed that molasses could be used as a carbohydrate source for the production of citric acid. Strain type, addition of whey, methanol and tricalcium phosphate had a significant impact on citric acid production by A. niger.
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To determine which citric acid-producing strain of Aspergillus niger utilized wet corn distillers grains most effectively to produce citric acid.Citric acid and biomass production by the fungal strains were analysed on the untreated grains or autoclaved grains using an enzyme assay and a gravimetric method respectively. Fungal citric acid production on the grains was found to occur on the untreated or autoclaved grains. The highest citric acid level on the grains was produced by A. niger ATCC 9142. The autoclaved grains supported less citric acid production by the majority of strains screened. Biomass production by the fungal strains on the untreated or autoclaved grains was quite similar. The highest citric acid yields for A. niger ATCC 9142, ATCC 10577, ATCC 11414, ATCC 12846 and ATCC 26550 were found on the untreated grains. Treatment of the grains had little effect on citric acid yields based on reducing sugars consumed by A. niger ATCC 9029 and ATCC 201122.It is feasible for citric acid-producing strains of A. niger to excrete citric acid on wet corn distillers grains whether the grains are treated or untreated. The most effective citric acid-producing strain of A. niger was ATCC 9142.The study shows that the ethanol processing co-product wet corn distillers grains could be utilized as a substrate for the commercial production of citric acid by A. niger without treatment of the grains.
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Background: Citric acid production through fermentation is economical but meeting its increasing global demand has been challenging in recent times.
Aim: This study aimed to screen Aspergillus and Candida sp. isolated from different sources with potentials of producing citric acid.
Methodology: Aspergillus and Candida spp. were isolated from compost soil and fruits (cucumber and banana) and their morphological characteristics were described using standard microbiological methods. The isolates were quantitatively screened for citric acid production based on appearance of yellow zone of clearance for 3 days. All the isolates which had acid unitage (AU) values> 5.0 were selected for further characterization using molecular methods.
Results: Candida tropicalis, Aspergillus sp. A. niger and Penicillium sp. were isolated from the soil and fruit samples. The isolates screened for citric acid production displayed varying diameters of yellow zones around their colonies is indicative of varying capability of the microbial strains. A. niger from compost soil which had highest AU value of 8.5 at Day 3 demonstrated greatest potential to yield citric acid. Molecular characterization revealed high citric acid producing strains as Aspergillus niger (EU440768.1) and Aspergillus welwitschiae (MG669181.1).
Conclusion: Although Aspergillus niger is widely utilized for industrial production of citric acid, this study has demonstrated that A. welwitschiae is a specie of Aspergillus capable of synthesizing citric acid reasonably.
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An Aspergillus niger isolate was screened for citric acid production from glucose and the cultural conditions were manipulated for optimum citric acid production. Optimization studies improved citric acid yield by 13.34% from 12.81 g/l obtained during the screening test to 14.52 g/l obtained at the end of the optimization studies. Glucose concentration of 15%, pH of 5.5, methanol at 3% concentration (v/v) and agitation rate of 450 rpm were found to be more suitable for citric acid production by the Aspergillus niger isolate used in this studies. Keywords : Citric acid, Aspergillus niger , Submerged fermentation, cultural conditions
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