Production of citric acid by Aspergillus Niger Using Molasses as Substrate
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Date
2017-06
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AAU
Abstract
Citric acid is an organic acid with numerous industrial application. It is extensively used in the
food and beverage industry as it combines a pleasant taste with low toxicity and sweetness. It can
be produced from different materials like molasses that has sucrose content of 32%. In Ethiopia,
some of the molasses were used for ethanol production and other purposes, but the remaining has
been exported to abroad. This study investigated that the utilization of molasses to use as a raw
material for citric acid production under different fermentation conditions with submerged
fermentation method in the laboratory using 250mL Erlenmeyer flask as the small scale laboratory
fermentor by using Aspergillus niger. The effect of temperature (25, 30, and 35℃), fermentation
time (96, 144, 196h) and pH (2, 4, and 6) of fermentation condition for citric acid yield test result
were investigated. The experimental design was done by using Design Expert 6.0.8 software for
three factors and Response Surface with 3- level factorial design type in optimization study. The
minimum citric acid yield was found to be 20.23 g/L after the fermentation time of 96h,
temperature 25℃ and pH 2. A maximum citric acid yield of 40.08 g/L was achieved under selected
optimal condition of (fermentation time 156h, temperature 30℃ and pH 3.89) with high value of
combined desirability. From the model regression equation developed, the linear terms of
temperature, and time had a positive effect and a pH had a negative effect on response yield. The
quadratic terms (pure and interaction quadratic terms) had a negative effect on extraction yield
except fermentation time and pH interaction. Incubation time had a more weighty linear effect on
yield as compared to fermentation temperature and pH. The quality of the product obtained under
optimized condition was assessed with Atomic Absorption Spectroscopy (Buck of Scientific 210
VGP AAS, USA) and UV visible Spectrophotometer. The results revealed that the heavy metal
content of the sample was below detection limit except Iron and purity of 99.2% respectively. The
study indicated that utilization of molasses for citric acid production is considered not only as a
positive option in terms of reducing imported citric acid, but also, as an attractive option in means
of providing job opportunity and minimizing environmental pollution.
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Keywords
citric acid, Aspergillus niger, Molasses