Citric acid production

SmF Industrial production of organic acids by growing the microorganisms that produce the product in a submerged culture 

SsF Growth of microorganisms on moist solid particles, where the spaces between the particles contain a continuous gas phase and a minimum of visible water 

Conventional production of citric acid is complex and ecologically unsafe, as a result of the characteristics of the raw material used and concentrated acids and alkali being used throughout the entire process. The 

Abarca, M.L., Accensi, F., Cano, J., and Cabanes, F.J. 2004. Taxonomy and significance of black aspergilli. Antonie Van Leeuwenhoek 86 33-49. 

Alakomi, H.L., Skytta, E., Saarela, M., Mattila-Sandholm, T., Latva-Kala, K., and Helander, I.M. 2000. Lactic acid permeabilizes Gram-negative bacteria by disrupting the outer membrane. Applied and Environmental Microbiology 66 2001-2005. 

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Physiological Role of Citric Acid. Citric acid occurs ia the terminal oxidative metabolic system of virtually all organisms. This oxidative metabohc system (Fig. 2), variously called the Krebs cycle (for its discoverer, H. A. Krebs), the tricarboxyUc acid cycle, or the citric acid cycle, is a metaboHc cycle involving the conversion of carbohydrates, fats, or proteins to carbon dioxide and water. This cycle releases energy necessary for an organism s growth, movement, luminescence, chemosynthesis, and reproduction. The cycle also provides the carbon-containing materials from which cells synthesize amino acids and fats. Many yeasts, molds, and bacteria conduct the citric acid cycle, and can be selected for thek abiUty to maximize citric acid production in the process. This is the basis for the efficient commercial fermentation processes used today to produce citric acid. 

Let us consider Figure 5.3 again. Both pyruvate kinase and dtrate synthase (enzymes III and V) are inhibited by elevated ATP concentrations. During citric acid production ATP concentrations are likely to arise (ATP produced in glycolysis) and either of these enzymes could, if inhibited, slow down the process. In fact all of the evidence suggests that both enzymes are modified or controlled in some way such that they are insensitive to other cellular metabolites during citric add production. 

Medium requirements and environmental factors involved in citric acid production... 

Citric Acid Production in Solid State Fermentation... 

I 6 Aspects of Mechanisms, Processes, and Requirements for Zeolite Separation Table 6.2 Analysis of citric acid product by adsorption. 

Recognizing the need for a more economically and environmentally friendly citric acid recovery process, an adsorptive separation process to recover citric acid from fermentation broth was developed by UOP [9-14] using resin adsorbents. No waste gypsum is generated with the adsorption technique. The citric acid product recovered from the Sorbex pilot plant either met or exceeded all specifications, including that for readily carbonizable substances. An analysis of the citric acid product generated from a commercially prepared fermentation broth is shown in Table 6.2, along with typical production specifications. The example sited here is not related to zeolite separation. It is intent to demonstrate the impact of adsorption to other separation processes. 

The microorganism used was m Aspergillus strain, and Pfizer already had considerable experience nsmgAspergillus for citric acid production and other uses. 

Industrial citric acid production began in 1860 and for the next 60 years was dominated by Italian producers. The original production method was based on extraction from the juice of citrus fruits by adding calcium oxide (CaO) to form calcium citrate, Ca3(C6H507)2, as an insoluble precipitate that can then be collected by filtration. Citric acid can be recovered from... 

With hydrophobic polyurethanes, the only option is adhesion. The polyol and isocyanate environments producing hydrophobic polyurethanes by the prepolymer method are thought to be too severe for hving cells. As noted earher, the weaker adhesion of adsorption to a hydrophobic polyurethane can be an advantage. Sanroman compared die adsorption and entrapment techniques and determined that the adsorption technique was superior based on citric acid productivity and operational stability. 

Figure 20 shows a schematic of a novel membrane-integrated process for citric acid production from glucose syrups by Yarrowia lypolitica ATCC 20346, based on prolonged fed-batch fermentation carried out in a stirred bioreactor coupled to a MF unit equipped with tubular ceramic membranes, and disodium citrate recovery from MF permeates by ED (Moresi, 1995). 

FIG. 20 Flow sheet of a novel integrated membrane process for citric acid production from glucose syrups by Yarrowia lipolytica, as proposed by Moresi (1995). 

In solid-state, or Koji, fermentation, Aspergillus niger is grown on moist wheat bran (70-80% water) and produces citric acid in 5-8 days. This process is practiced only in Japan and accounts for about one-fifth of Japanese citric acid production. In liquid surface, or shallow... 

Xu TW and Yang WH. Effect of cell conUgurations on the performance of citric acid production by bipolar membrane electrodialysis. 

Xu TW and Yang WH. Citric acid production by electrodialysis with bipolar membranes. Chem. Eng. Process. 2002 41 519-524. 

Figure 5.4 suiranaiises the change occuring in A. niger in citric acid production mode when compared to ccmventional metabolism. It is worth studying the Bgure for some time because it explains some of the features necessary for a successful fermentaticm process. 

Shojaosadati, S. A. and Babaeipour, V. (2002). Citric acid production from apple pomace in multi-layer packed bed solid-state bioreactor. Process Biochem. 37, 909-914. 

Tran, C. T. and Mitchell, D. A. (1995). Pineapple waste—A novel substrate for citric acid production by solid-state fermentation. Biotechnol. Lett. 17(10), 1107-1110. 

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