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Effect of Biomass and Sugar in Citric Acid Production by Aspergillus Niger Using Molasses and Jackfruit as Substrates

M. Kamruzzaman Munshi
Food Technology Division, Institute of Food and Radiation Biology, Atomic Energy Research Establishment, Savar, Dhaka, Bangladesh

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

Roksana Huque
Food Technology Division, Institute of Food and Radiation Biology, Atomic Energy Research Establishment, Savar, Dhaka, Bangladesh

M. Mazibur Rahman
International Affairs Division, Bangladesh Atomic Energy Commission, Paramanu Bhaban, Dhaka, Bangladesh

Afifa Khatun
Food Technology Division, Institute of Food and Radiation Biology, Atomic Energy Research Establishment, Savar, Dhaka, Bangladesh

Mahfuza Islam
Food Technology Division, Institute of Food and Radiation Biology, Atomic Energy Research Establishment, Savar, Dhaka, Bangladesh

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

Abstract/ Executive Summary:

Under surface culture conditions, 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 day 13 without the 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 the various fermentation mediums. 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 a mutant strain of A. niger 14/20 than 79/20. In addition to this, wet-weight biomass was higher than dry-weight biomass. Without the presence of Prescott salt, the wet weight of the mycelial body of the fungus Aspergillus niger 14/20 was found highest on day 13 in mixed substrates which were 160.15. A 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 a 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 the presence of Prescott salt in the molasses, jackfruit, and mixed fermentation media during the 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 the 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.

Keywords: Citric acid, Aspergillus niger, Substrate, Prescott salt

Location: Food Technology Division, Institute of Food and Radiation Biology, Atomic Energy Research Establishment, Savar, Dhaka, Bangladesh

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Jackfruit

Objectives:

The present investigation was, therefore, undertaken with a view to determining the feasibility of using raw and cheap materials such as molasses and jackfruit for citric acid production and optimization under fermentation conditions on these substrates.

Methodology:

2.1. Microorganism Used Citric acid-producing strains of A. niger designated as 14/20 and 79/20 (Hannan et al., 1973) were used in this present 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 (Hannan et al., 1973 and Begum et al., 1988). The culture was maintained on agar slants containing 1% malt extract, 1% yeast extract, 1.5% dextrose and 2.5% bacto agar. 2.2. Substrates Used: (a) Cane Molasses (b) Jackfruit Cane molasses containing 20% water, 62% sugar, nonsugar contents 10% and 8% inorganic salts (ash contents), making a blackish homogenous liquid with high viscosity. Ash contents include ions such as Mg, Mn, Al, Fe and Zn in the variable ratio (Prescott and Dunn’s, 1987). The other substrate bright yellow-colored jackfruit was used in the experiments for the comparative study. 2.3. Fermentation Medium 2.3.1. Preparation of Molasses Medium Molasses was clarified by appropriate dilution with water and boiled 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. 2.3.2. Preparation of Jackfruit Medium Jackfruit was washed with tap water several times. Thereafter jackfruit was sliced thinly and dried in dryer at 50°C. The substrate was powdered by using a grinding machine. Dried powder of jackfruit was hydrolyzed separately in 300ml solution of 0.05N HCl and autoclaved at 121°C temperature, 15 Ibs pressure for 20 minutes. The hydrolyzed materials were then filtered through a thin cloth. 2.3.3. Preparation of Mixed Substrate Medium Equal amount of jackfruit and molasses were hydrolyzed in 300ml solution of 0.05N HCl and autoclaved at 121°C temperature, 15 lbs pressure for 20 minutes. The hydrolyzed materials were then filtered through a thin cloth. The media was then kept overnight for sedimentation of suspended particles resides in molasses. Experiments carried out for the following substrates: (i) Molasses in presence of Prescott salt (ii) Molasses without the presence of Prescott salt (iii) Jackfruit in presence of Prescott salt (iv) Jackfruit without the presence of Prescott salt (v) Mixed in presence of Prescott salt and (vi) Mixed without the presence of Prescott salt. Initially, 14% sugar, pH 5 and incubation temperature (30ºC) were optimized in case of all used media and the given strains for citric acid fermentation. 14% sucrose solution was found to better moisture level for citric acid fermentation [11]. A concentration higher than 14 to 18 % however, leads to a greater amount of residual sugar making the process uneconomical and when the concentration of the media is more than needed it to become inhibitory for citric acid production. And as a result citric acid production also decreases. In the present study, the molasses, jackfruit and mixed substrate media were prepared with calculating the 14% sugar concentration first and thus the high yield of citric acid was produced[12] investigated that in respect to citric acid production all the strains (318, 79/20, 14/20 and CA16 wild) gave more citric acid at pH 5 than the other pH values (3.5, 4.0, 4.5). In the present study, pH 5 in molasses, jackfruit and mixed substrate media was maintained for optimum production of citric acid. The optimum temperature range of 26-30°C has been proposed for good citric acid yields and rapid rate of accumulation (Doelger and Prescott, 1934). A temperature of 30ºC was found to be the best for citric acid fermentation (Qp = 0.667 ± 0.02a g/l/h) [13]. 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 (NH4NO3, 2.23g/l; K2HPO4, 1.00g/l, and MgSO4.7H2O, 0.23g/l). Fermentation was carried out in 100ml conical flasks containing 25ml medium. Titration was done from day 7 of incubation. Total titrable acid values were determined by freshly prepared 0.1N NaOH. Citric acid and residual sugar were estimated between 3-13 days of culture broth by the Marrier and Boulet method (1958) and Anthrone sulphuric acid method (Morse, 1947) respectively.

Source of Information: American Journal of Food and Nutrition, 2013, Vol. 1, No. 1, 1-6

Article Link (Online Journal): DOI:10.12691/ajfn-1-1-1

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The production of citric acid was not the same in all fermentation mediums. Without the presence of Prescott salt, the highest citric acid production was found in mixed fermentation medium throughout the fermentation period and the lowest production of citric acid was found in molasses media. Whereas with the presence of Prescott salt lowest production of citric acid was found in jackfruit medium and the highest amount of citric acid was produced in molasses medium throughout the fermentation period. And in both cases, A. niger 79/20 produces a lower amount of citric acid than A. niger 14/20. From the experiments, it can be opined that both molasses and jackfruit could be used for the production of citric acid but in the case of the mixed substrate, the citric acid production is much economically feasible and was proved more potential for citric acid production. It is apparent from the results that the maximum yield of citric acid was also dependent on sugar level and biomass.

Knowledge Management: Journal