University of Khartoum

Optimization of Fermentation Conditions for Citric Acid Production by Aspergillusniger in Submerged Culture

Optimization of Fermentation Conditions for Citric Acid Production by Aspergillusniger in Submerged Culture

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Title: Optimization of Fermentation Conditions for Citric Acid Production by Aspergillusniger in Submerged Culture
Author: ShazaGamal Mohammed, Ali
Abstract: The objective of this study was to optimize citric acid production by Aspergillus niger in submerged culture. During this study, six presumptive isolates of A. niger were recovered from different sources, and were characterized by microscopic and cultural characteristics on different growth media. Results of characterization indicated that the presumptive isolates colonies were powdery in texture, with a black surface and pale yellow underneath. Microscopic examination showed that each presumptive isolate consisted of a substrate white mycelia from which vertical hyphae grow and carry at its tip globose heads with smooth hyaline stipes, spherical vesicles, packed metulae and short phialides that carry globose to elliptical conidia. Idtinification and characterization was confirmed by sequencing of the 18s ribosomal RNA gene. Partial sequencing of 18s rRNA of each isolate was aligned to the reference isolate ATCC 9763. Phylogenetic analysis showed that the highest homology (99 %) was obtained by isolates KU1 and KU8, low identity percentage (93%) was observed for isolate KU3. RAPD-PCR divided the isolates into three groups. The band patterns obtained were consistent and reproducible, their numbers varied between 4 to 14 and the size of the fragments was in the range of 1000 – 1500 bp.The isolates were screened for citric acid production using Czapek-Dox medium under submerged conditions. The results indicated that all isolates were able, although to variable efficiencies, to convert sucrose to citric acid. Based on the results of this experiment, only one isolate (KU 2) was selected for further studies. Optimization of media constituents and other fermentation conditions were studied in submerged culture using Czapek-Dox medium. Results of optimization experiments indicated that optimum citric acid concentration of (g/l) 26.7, 17.8, 23.7, 29.1, 28.9 were obtained at 10 % sucrose, pH 5, 30°C, 0.3% Na NO3 and 4% ethanol, respectively. Optimum medium volume and optimum inoculum level were 25 ml in 250 ml vessel and 2.5 %, respectively. Maximum citric acid concentration of 51.3g/l was obtained when fermentation period was kept for 144h. El-Genaid cane molasses was tested as a substrate for citric acid fermentation. H2 SO4 treated molasses supplemented with 4 % ethanol gave 56 g/l citric acid in shake flask. Scale up of citric acid production was conducted in 5 L stirred fermentor and Czapek Dox medium was used as a fermentation substrate supplemented with 100g/l sucrose. Maximum amount of citric acid (50.01 g/l) was produced after144hrs and dry mycelium weight was 26.86 g/l while sugar consumed was 61.52 g/l with 81.65 % yield. Results reported validates that the process of citric acid production by fermentation can be explored for commercialization.
Description: 126page
URI: http://khartoumspace.uofk.edu/handle/123456789/13035
Date: 2015-06-16


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