Statistical Optimization of Process Parameters for Citric Acid Synthesis from Water Hyacinth Using Solidstate Fermentation
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Date
2024-04
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Addis Ababa University
Abstract
Citric acid is a versatile organic compound widely employed across various industries, with
its primary application residing in the food sector. This organic acid exhibits remarkable
attributes such as high solubility, palatability, and low toxicity, rendering it invaluable in the
realms of food, biochemistry, and pharmaceuticals. The principal objective of this study is to
synthesize citric acid using the fungus Aspergillus niger, utilizing water hyacinth as the
primary substrate, and to assess the resulting citric acid's quality and concentration. In the
laboratory setting, we harnessed the solid-state fermentation method within 250 mL
Erlenmeyer flasks to transform water hyacinth into citric acid. To systematically analyze and
optimize the synthesis process, Design Expert 13.0.5.0 was employed, applying Response
Surface Methodology (RSM) to study the concurrent impact of key variables: incubation time
(3 days, 6 days and 9 days), fermentation temperature (set at 25⁰C, 30⁰C and 35⁰C), and pH
levels (2, 4 and 6). The study utilized a three-variable, three-level Box-Behnken design to
establish a statistical model that elucidates the relationship between citric acid concentration
and these independent variables while optimizing the production process. The statistical
model proved significant (p < 0.0001) and demonstrated low standard deviation (0.3445).
Notably, it exhibited no lack of fit (R2=0.9959), and the predicted R-Squared value of 0.9907
closely aligned with the Adj R-Squared of 0.9514. Citric acid production showcased
significance under moderate levels of incubation time, fermentation temperature, and pH.
Analysis of the model's regression equation highlighted the positive influence of temperature
and time, while pH exhibited a negative effect on the yield of the desired response. Through
rigorous experimentation, we achieved a maximum citric acid yield of 22.205 g/L under the
optimal conditions, which included an incubation time of 7.375 days, a fermentation
temperature of 31.071 ⁰C, and a pH level of 4.245. These settings yielded a combined
desirability of high value. The validation process confirmed the statistical model's reliability,
demonstrating an insignificant difference between experimental and model-predicted results.
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Keywords
Citric acid, Aspergillus niger, water hyacinth, Substrate, Solid State Fermentation