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Effect of Gamma-ray Induced Mutant Strains of Aspergillus Niger on Citric Acid Fermentation Using Molasses and Jackfruit Based Medium

M. Kamruzzaman Munshi
Food Technology Division, Institute of Food and Radiation Biology, 1 Atomic Energy Research Establishment, GPO Box 3787, Savar, Dhaka-1000. Bangladesh

Md. Fuad Hossain
Department of Micrbiology, Jahangirnagar University, Savar, Dhaka, Bangladesh

Roksana Huque
Food Technology Division, Institute of Food and Radiation Biology, 1 Atomic Energy Research Establishment, GPO Box 3787, Savar, Dhaka-1000. Bangladesh

Mazibur Rahman
International Affairs Division, Bangladesh Atomic Energy Commission, Paramanu Bhaban, Dhaka-1207

Afifa Khatun
Food Technology Division, Institute of Food and Radiation Biology, 1 Atomic Energy Research Establishment, GPO Box 3787, Savar, Dhaka-1000. Bangladesh

Mahfuza Islam
Food Technology Division, Institute of Food and Radiation Biology, 1 Atomic Energy Research Establishment, GPO Box 3787, Savar, Dhaka-1000. Bangladesh

M. Afzal Hossain
Food Technology Division, Institute of Food and Radiation Biology, 1 Atomic Energy Research Establishment, GPO Box 3787, Savar, Dhaka-1000. Bangladesh

Md. Ibrahim Khalil
Department of Biochemistry and Molecular Biology, Jahangirnagar University, Savar, Dhaka, Bangladesh

Abstract/ Executive Summary:

Aspergillus niger is most commonly known among the various fungal strains screened for citric acid production when cultivated in the 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 day 13 but it was higher than that produced by the unirradiated strain. In absence of Prescott salt, the highest production of citric acid was found by further mutated A. niger 79/20 with gamma radiation at 20 Krad in a mixed fermentation medium which was about 15.94 mg/ml. The 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 day 13 but it was higher than that produced by the unirradiated strains.

Keywords: Gamma Radiation, Citric Acid, Aspergillus niger, Molasses, Jackfruit

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End Date:

Program Area: Quality and Nutrition

Commodity: Jackfruit

Objectives:

So the purpose of the present study was to describe the feasibility of using raw and cheap materials such as molasses and jackfruit for citric acid fermentation and to use gamma-ray induced mutants for further genetic improvement of the high citric acid yielding mutant strains 14/20 and 79/20 of A. niger.

Methodology:

Microorganisms Used: Citric acid-producing strains of A. niger designated as 14/20 and 79/20 were used in this study. 14/20 and 79/20 are second step mutants derived from the strain HB3 which is the first step mutant from the wild type strain CA16. The culture was maintained on agar slants containing 1% malt extract, 1% yeast extract, 1.5% dextrose and 2.5% bacto agar. Substrates Used: (a) Cane molasses and (b) Jackfruits. Fermentation medium: Preparation of Molasses Medium: Molasses was clarified by appropriate dilution with tap water and boil the solution for half an hour. The clarified molasses was then kept overnight for sedimentation of suspended particles. In order to remove the coarse particle in the solution, it was filtered through absorbent cotton and sediment was discarded. Preparation of Jackfruits Medium: Jackfruits were washed with tap water. Then jackfruits were sliced thinly and dried in a dryer at 50°C. The substrates were powdered hydrolyzed separately in 300 ml solution of 0.05 N HCl and autoclaved at 121°C temperature, 15 Ibs pressure for 20 minutes. The hydrolyzed materials were then filtered through the thin cloth. Preparation of mixed substrate medium: Equal amounts of jackfruits and molasses were hydrolyzed in 300 ml solution of 0.05 N HCl and autoclaved at 121°C temperature, 15 Ibs pressure for 20 minutes. The hydrolyzed materials were then filtered through the thin cloth. The media was then kept overnight for sedimentation of suspended particles resides in molasses. The following parameters were selected to find out which one was better for citric acid fermentation: Sugar with Prescott salt and Sugar without Prescott salt (NH 4 NO 2.23 g/l; K HPO 1.00 g/l and MgSO . 7H O, 0.23 g/l) 3, 2 4, 4 2 Irradiation of the Organism and Further Induction of High Yielding Mutants: With the help of gamma rays, several high citric acid yielding mutants of A. niger (HB3, 14/20 and 79/20 etc.) have been isolated and their preliminary characterizations, semi-pilot scale studies in cane molasses medium were made. Recently, the induction of further mutation for a higher yield of citric acid has been attempted using mutant strains 14/20 and 79/20. Conidia were irradiated with gamma radiation at 10, 20, 30 and 40 Krad / hour by Co Gamma beam-650 60 sources. The strain was sub-cultured on dextrose-agar slants containing 1% malt extract, 1% yeast extract, 1.5% dextrose and 2% bacto agar. Conidia were harvested in sterile distilled water after 7-9 days of growth at 30°C and inoculated to the fermentation media. 1 ml spore suspension was taken from the tube by micropipette and dropped into fermentation media. Cane molasses, jackfruit and cane molasses-jackfruit mixed media were used for fermentation. A gamma-ray is a packet of electromagnetic energy (photon) emitted by the nucleus of some radionuclides following radioactive decay. After gamma-irradiation and the breaking of the DNA double-strands, the cell can repair the damaged genetic material in the limit of its capability and genetic improvement may occur. Citric Acid Production Process: In this production technique, which is still the major industrial route to citric acid used today, cultures of A. niger were fed on sucrose to produce citric acid.

Source of Information: Academic Journal of Nutrition 1 (3): 23-28, 2012

Article Link (Online Journal): DOI: 10.5829/idosi.ajn.2012.1.3.7191

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Achievement/Findings:

The present study showed that a higher yield of citric acid as desired from an industrial point of view could be obtained from molasses and jackfruit of Bangladesh and hence the possibility of profitable utilization of cane molasses and jackfruit for citric acid production in Bangladesh could be explored by using mutationally improved strains of A. niger.

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