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Citric Acid Production by Aspergillus Niger Through Solid-state Fermentation on Sugarcane Bagasse

Abdullah-Al-Mahin
Microbiology & Industrial Irradiation Division, Institute of Food & Radiation Biology (IFRB), Atomic Energy Research Establishment (AERE), PO Box 3787, Dhaka 1000, Bangladesh,

Shek Mehdi Hasan
Departmetnt of Biotechnology & Genetic Engineering, Islamic University, Kustia 7003, Bangladesh.

Mahboob Hossain Khan
Departmetnt of Biotechnology & Genetic Engineering, Islamic University, Kustia 7003, Bangladesh.

Rehana Begum
Microbiology & Industrial Irradiation Division, Institute of Food & Radiation Biology (IFRB), Atomic Energy Research Establishment (AERE), PO Box 3787, Dhaka 1000, Bangladesh,

Abstract/ Executive Summary:

Four isolates of Aspergillus niger (viz., CA16, 14/20, HB3 and 318) were used for citric acid production using sugarcane bagasse as a substrate and sucrose solution as a moistening agent. Using 3 g of sugarcane bagasse as substrate, the highest citric acid production was obtained when 10 ml of 14% sucrose solution was used as moistening agent. Maximum citric acid production was found after 11 days fermentation for all isolates of A. niger. Both sugar utilization as well as citric acid production was found highest in the presence of Prescott salt by A. niger 318 (196.21 μg/g), followed next by A. niger 14/20 (103.06 μg/g). However, in absence of Prescott salt both sugar utilization and citric acid production was highest (50.01 μg/g) by A. niger 14/20. In general, extension of the fermentation (up to 11 days) resulted in an increase in citric acid, total titratable acid and biomass, and decrease in both residual sugar concentrations.

Keywords: Citric acid, Solid-state fermentation, Aspergillus niger, Sugarcane bagasse

Location:

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Sugarcane

Objectives:

To investigate the possibility of using sugarcane bagasse as a substrate fortified with different quantity of sucrose solution as moistening agent and additional carbon source for solid-state fermentation for citric acid production by four isolates of A. niger.

Methodology:

Microorganisms used :Four citric acid-producing isolates of Aspergillus niger were used in the present study. An isolate designated as CA1620-21 used as the original parent organism, which was a natural isolate from local soil. Other three isolates of A. niger designated as 14/20, HB3 and 31822-23 were the radiation mutant of A. niger CA16. The isolates were maintained on agar slant medium containing 1% malt extract, 1% yeast extract, 1.5% dextrose and 2% agar, stored at 4°C and sub-cultured fortnightly.

Citric acid production medium: Sugarcane bagasse collected from Rajshahi Sugar Mill was sundried; cut into small pieces, grounded and screened to collect a particle size of about 1.2-1.6 mm. Bagasse (3 g) was taken in 250-ml Erlenmeyer flasks and moistened with different volume of 14% sucrose to set the desired moisture level. Separate sets of media were enriched with Prescott salt (NH4NO₃, 2.23 g/l; K₂HPO₄, 1.00 g/l and MgSO₄.7H₂O, 0.23 g/l). The pH of the medium was adjusted at 3.5 and autoclaved.

. Inoculum:Spore suspension of the concentration 2 x 107 spores/ml prepared from 8 to 10-day-old cultures of A. niger was used as inoculum in each experiment.

Solid-state fermentation: Each flask containing citric acid production medium was inoculated with 1 ml of spore suspension followed by mixing and incubation at 30°C in the a humidity-controlled incubator for 11 days.

Analytical techniques: Initial and residual sugar concentrations, total titratable acidity (TTA) and citric acid produced by fermentation were estimated by the method of anthrone-sulphuric acid method24 and Marrier and Boulet method25 respectively from 5-11 days. In addition to these, dry weight of medium after fermentation was also carried out.

Source of Information: Bangladesh J Microbiol, Volume 25, Number 1, June 2008, pp 9-12

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Using 3 g of sugarcane bagasse as substrate, the highest citric acid production was obtained when 10 ml of 14% sucrose solution was used as moistening agent. Maximum citric acid production was found after 11 days fermentation for all isolates of A. niger. Both sugar utilization as well as citric acid production was found highest in the presence of Prescott salt by A. niger 318 (196.21 μg/g), followed next by A. niger 14/20 (103.06 μg/g). However, in absence of Prescott salt both sugar utilization and citric acid production was highest (50.01 μg/g) by A. niger 14/20. In general, extension of the fermentation (up to 11 days) resulted in an increase in citric acid, total titratable acid and biomass, and decrease in both residual sugar concentrations.

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