Citric acid formation

The diagram looks very promising in terms of citric acid formation in that a-oxoglutarate dehydrogenase is inactive, isodtrate dehydrogenase has veiy low activity and aconitase equilibrates 90% towards dtric add. 

Match each of the following statements with a process for citric acid formation using A. rtiger. 

Complexing and chelating agents Cyclodextrins EDTA Salicylates Citric acid Formation of inclusion complexes Increase of stability Increase paracellular transport by Removing calcium ions Widening of tight junctions... 

Jadhav and Magar (463) applied an ascorbic acid glaze, which delayed the yellow discoloration and allied organoleptic changes, to frozen white pomfret, surmai, and mackerel fish. Use of phosphates in combination with ascorbate esters has been declared to improve the color and flavor of fish products (464). Shellfish (465,466,467) including prawns and breaded shrimp, have been ascorbic acid treated, the latter in combination with citric acid. Formation of dimethylnitrosamine in Alaskan pollack roe (468) was inhibited when ascorbic acid was in-... 

Smith, A. H., and Orten, J. M, The rate of citric acid formation following the injection of the sodium salts of certain dicarboxylic acids. J. Biol. Chem. 124, 43 (1938). 

Since pyruvic acid carboxylation via the malic enzyme is the main source of oxaloacetate, slow glycolysis may result in deceleration of the Krebs cycle. The slowing down of glycolysis may result from reduced enzyme activity or from insufficient amounts of substrate the former possibility has been eliminated by the experiments of Chaikoff and his group. These investigators injected lactate, pyruvate, and acetate, and measured their conversion to CO2. They observed that CO2 formation was the same in diabetics as in nondiabetics. Insufficiency of Krebs cycle substrate is also unlikely, because CO2 production, which is derived mainly from the tricarboxylic acid cycle, is unimpaired in diabetes. In addition to being used for citric acid formation, acetyl CoA is also a key building block for fatty acids. 

Poulsen L, Dai Z, Panisko E, et al. Transcriptome and proteome analysis of the correlation between citric acid formation and manganese limitation in Aspergillus niger. Regulatory processes in Aspergillus niger 2012 43-61. 

Citric acid is a major end product of the oxidative metabolism of carbohydrate, ethanol, and acetic acid in many molds, e.g., Aspergillus niger. Evidence of the mechanism of citric acid formation is incomplete but the existing data are compatible with the assumption that citric acid arises, as an animal tissue, by condensation of oxalacetate with active acetic acid, as first proposed by Raistrick and Clark. Experiments with isotopic CO2 on Aspergillus suggest that the oxalacetate required for the synthesis of citrate can be formed by the carboxylation of pyruvate formed as an intermediate in the anaerobic fermentation.It is very... 

Ramakrishnan CV, Steel R, Lentz CP (1955) Mechanism of citric acid formation and accumulation m Aspergillus niger. Archiv Biochem Biophys 55 270-273 Agnello LA, Kieber BJ (1961) Citric acid. Ind Eng Chem 53 253-258 Clark DS (1962) Submeiged citric acid fermentation of sugar beet molasses. Effect of fer-rocyanide control. Ind Eng Chem Res Dev 1 59-62... 

Martin SM, Wilson PW, Burris RH (1950) Citric acid formation from C Oj hy Aspergillus niger. Arch Biochem 26 103-111... 

Hunter FE, Leloir LF (1945) Citric acid formation from acetoacetic and oxalacetic acids. J Biol Chem 159 295-310... 

Certain factors and product precursors are occasionally added to various fermentation media to iacrease product formation rates, the amount of product formed, or the type of product formed. Examples iaclude the addition of cobalt salts ia the vitamin fermentation, and phenylacetic acid and phenoxyacetic acid for the penicillin G (hen ylpenicillin) and penicillin V (phenoxymethylpenicillin) fermentations, respectively. Biotin is often added to the citric acid fermentation to enhance productivity and the addition of P-ionone vastly iacreases beta-carotene fermentation yields. Also, iaducers play an important role ia some enzyme production fermentations, and specific metaboHc inhibitors often block certain enzymatic steps that result in product accumulation. 

Certain compounds, known as chelating agents (qv), react synergisticaHy with many antioxidants. It is beheved that these compounds improve the functional abiUties of antioxidants by complexing the metal ions that often initiate free-radical formation. Citric acid and ethylenediaminetetraacetic acid [60-00-4] (EDTA), C2QH2gN20g, are the most common chelating agents used (22). 

Citrates. Iron citrate [2338-05-8] is a compound that contains citric acid and iron(II) and iron(III) in indefinite ratios. Iron(II) citrate [23383-11-1] and iron(III) citrate [28633-45-6] are also of indefinite stoichiometry, although iron(III) citrate which contains Fe and citric acid in a 1 1 ratio [3522-50-7] is known. These compounds dissolve slowly in water and are more readily soluble in hot water. The solution chemistry of these compounds is comphcated by formation of a number of monomeric and oligomeric species. All of the iron citrate compounds are used as supplements to soils and animal diets. 

The lanthanides form many compounds with organic ligands. Some of these compounds ate water-soluble, others oil-soluble. Water-soluble compounds have been used extensively for rare-earth separation by ion exchange (qv), for example, complexes form with citric acid, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEEDTA) (see Chelating agents). The complex formation is pH-dependent. Oil-soluble compounds ate used extensively in the industrial separation of rate earths by tiquid—tiquid extraction. The preferred extractants ate catboxyhc acids, otganophosphoms acids and esters, and tetraaLkylammonium salts. 

Salt Formation. Citric acid forms mono-, di-, and tribasic salts with many cations such as alkahes, ammonia, and amines. Salts may be prepared by direct neutralization of a solution of citric acid in water using the appropriate base, or by double decomposition using a citrate salt and a soluble metal salt. 

Chelate Formation. Citric acid complexes with many multivalent metal ions to form chelates (9,10). This important chemical property makes citric acid and citrates useful in controlling metal contamination that can affect the color, stabiUty, or appearance of a product or the efficiency of a process. 

Seafood. Citric acid is used in combination with other preservatives/antioxidants to lower the pH to retard microbial growth, which can lead to spoilage, formation of off-flavors, and colors on fish and other seafood products. 

Petroleum. Citric acid is added to hydrochloric acid solutions in acidising limestone formations. Citric acid prevents the formation of ferric hydroxide gel in the spent acid solution by chelating the ferric ions present. Formation of the gel would plug the pores, preventing the flow of oil to the producer well (123—127). 

StiU another possible role of supersaturation is that it affects the solution stmcture and causes the formation of clusters of solute molecules. These clusters may participate in nucleation, although the mechanism by which this would occur is not clear. Evidence of the existence of cluster formation in supersaturated solutions has been presented for citric acid (21) while others have examined the phenomenon in greater detail (22,23). 

Citric acid is a nontoxic metabohc product of the body (Krebs or citric acid cycle), and it has been approved by FDA for its use in humans. It was found that the citric acid can be reacted with a variety of hydroxyl-containing monomers at relatively mUd conditions. " Citric acid can also participate in hydrogen bonding interactions within a polyester network. Citric acid was chosen as a multifunctional monomer to enable network formation. 

Glucose is metabolized to pyruvate by the pathway of glycolysis, which can occur anaerobically (in the absence of oxygen), when the end product is lactate. Aerobic tissues metabolize pyruvate to acetyl-CoA, which can enter the citric acid cycle for complete oxidation to CO2 and HjO, linked to the formation of ATP in the process of oxidative phosphorylation (Figure 16-2). Glucose is the major fuel of most tissues. 

Pathways are compartmentalized within the cell. Glycolysis, glycogenesis, glycogenolysis, the pentose phosphate pathway, and fipogenesis occur in the cytosol. The mitochondrion contains the enzymes of the citric acid cycle, P-oxidation of fatty acids, and of oxidative phosphorylation. The endoplasmic reticulum also contains the enzymes for many other processes, including protein synthesis, glycerofipid formation, and dmg metabolism. 

The citric acid cycle (Krebs cycle, tricarboxylic acid cycle) is a series of reactions in mitochondria that oxidize acetyl residues (as acetyl-CoA) and reduce coenzymes that upon reoxidation are linked to the formation of ATP. 

The citric acid cycle is an integral part of the process by which much of the free energy liberated during the oxidation of fuels is made available. During oxidation of acetyl-CoA, coenzymes are reduced and subsequendy reoxidized in the respiratory chain, hnked to the formation of ATP (oxicktive phosphorylation see Figure 16-2 and also Chapter 12). This process is aerobic, requiring oxygen as the final oxidant of the reduced coenzymes. The enzymes of the citric acid cycle are lo-... 

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