Insight into citric acid: A versatile organic acid

Microbial Degradation and Value Addition to Food and Agriculture Waste

Improvement of citric acid production by Aspergillus niger with addition of phytate to beet molasses

Simultaneous saccharification and citric acid production from paper wastewater pretreated banana pseudostem: Optimization of fermentation medium formulation and kinetic assessment.

The ability of Aspergillus niger strains to support citric acid production using solid-state fermentation of agricultural processing coproducts was examined in this review. Citric acid has been shown to have a number of commercial applications in the food and beverage industries. The A. niger strains capable of elevated citric acid production are known to contain genetic mutations that stimulate overproduction of the organic acid likely involving citric acid cycle reactions. The agricultural processing coproducts previously examined for their ability to support citric acid production by A. niger solid-state fermentation include fruit processing wastes, sugarcane bagasse, starch vegetable processing wastes and cereal grain processing coproducts. A comparison of citric acid production by A. niger strains using solid-state fermentation demonstrated that certain agricultural processing coproducts were more effective in supporting a high level of acid synthesis. In particular, fruit processing wastes, such as apple pomace, banana peels, grape pomace and orange peels, supported high levels of citric acid by the fungal strains following solid-state fermentation. On the other hand, processing coproducts of cereal grains, such as brans and ethanol processing coproducts, supported low levels of citric acid production by the A. niger strains using solid-state fermentation. It appeared that the cereal processing coproducts provided less available sugar content to support citric acid production by the fungal strains. It was concluded that the level of citric acid produced by the A. niger strains during solid-state fermentation was dependent on the sugar content of the agricultural processing coproduct utilized.

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Citric Acid Production by Aspergillus niger Using Solid-State Fermentation of Agricultural Processing Coproducts

Increasing cost of production and global demand for citric acid is driving research towards optimizing process conditions to yield very high quantity of the organic acid using abundant cheap substrates and selected microorganisms.  Consequently, this study was designed to optimize the production of citric acid by making use of banana (Musa acuminata) peels (agro-waste) through means of solid state fermentation  involving  Aspergillus  niger  (Model  A)  and Candida tropicalis (Model B). In this study, a two-level, five-variable full factorial design of response surface methodology (RSM) comprising 32 experimental runs for each model were used to develop a statistical model for the optimization of fermentation conditions which include: pH, glucose, zinc, ammonium chloride and methanol. The results obtained indicate that a second order polynomial model fitted adequately and statistically significant (p<0.0001) and (p<0.0410) for Model A and B, respectively. The optimum values of the variables were: pH 4; glucose 5% w/v; zinc 2% w/v; ammonium chloride 0.5% w/v; and methanol 3% v/v. Under these conditions, the concentration of citric acid produced were 97.6 g/L with a pH of 3.85 using Aspergillus niger and 113.6 g/L with a pH of 3.45 using Candida tropicalis at 10days fermentation period. Experimental validation of the model indicated that no difference exist between the predicted and the actual yield results. Therefore, utilization of low-cost agro-waste banana peel which serve as suitable substrate for optimization of citric acid production is advocated because of their advantages such as income generation, reduction  in  environmental  problems  posed  by  food-waste  disposal  and  public  health  hazards associated with it.

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Gift Uzah

Papers

Optimization of Citric Acid Production by Aspergillus niger and Candida tropicalis for Solid State Fermentation Using Banana Peel Substrate