Citric acid naturally occurring

Citric acid occurs widely in the plant and animal kingdoms (12). It is found most abundantiy in the fmits of the citms species, but is also present as the free acid or as a salt in the fmit, seeds, or juices of a wide variety of flowers and plants. The citrate ion occurs in all animal tissues and fluids (12). The total ckculating citric acid in the semm of humans is approximately 1 mg/kg body weight. Normal daily excretion in human urine is 0.2—1.0 g. This natural occurrence of citric acid is described in Table 7. 

Different organic acids, primarily lactic acid, have been successfully used for decontamination of whole livestock carcasses, and the application of different organic acids used for decontamination has also been tested in the fruit and vegetable industry. Organic acids other than lactic acid that are known to have bactericidal effects are acetic, benzoic, citric, malic, propanoic, sorbic, succinic and tartaric acids (Betts and Everis 2005). The antimicrobial action is due to a reduction in the pH in the bacterial environment, disruption of membrane transport, anion accumulation or a reduction in the internal pH in the cell (Busta et al., 2001). Many fruits contain naturally occurring organic acids. Nevertheless, some strains, for example E. coli 0157, are adapted to an acidic environment. Its survival, in combination with its low infective dose, makes it a health hazard for humans. 

Brookhaven National Laboratory s (BNL s) biochemical recovery of radionuclides and heavy metals is a patented biochemical recovery process for the removal of metals and radionuclides from contaminated minerals, soil, and waste sites. In this process, citric acid, a naturally occurring organic complexing agent, is used to extract metals and radionuclides from solid wastes by the formation of water-soluble, metal-citrate complexes. The complex-rich extract is then subjected to microbiological biodegradation that removes most of the extracted heavy metals. 

These acids are found ready-made in nature in great numbers. Some of them occur as free acids (citric acid, tannic acid, malic acid), others as esters (products of acids and alcohols, such as fats and oils and the flavors of many fruits and the odors of many flowers). Still other of these organic acids are produced by the action of bacteria (acetic acid from wine or cider, lactic acid when milk turns sour, butyric acid in rancid hutter). 

Citric acid is the most widely used acid in fruit-flavoured beverages. It has a light fruity character that blends well with most fruit flavours, which is to be expected as it occurs naturally in many fruit types. For example, unripe lemons contain 5-8% citric acid. It is also the principal acidic constituent of such fruits as blackcurrants... 

The first problem was solved 133) through synthesis (followed by enzymatic degradation) of tritiated citric acid stereospecifically labeled in the pro-R branch, as indicated in Fig. 62. The starting material for this synthesis is the naturally occurring 5-dehydro-... 

Fumaric acid is a naturally occurring sour-tasting compound found in many plants such as Fumaria officinalis L. (Fumariaceae), Boletus scaber Bull. (Boletaceae), and Fames igniaries (Fries) Kickx. (Pluporaceae). It is an essential component for respiration in plant and animal tissues. It is produced by fermentation with mold, such as Rhizopus nigricans, or by chemical synthesis. It is also used in soft drinks and ice cream and as an acidulant along with citric acid. 

Citric acid and zingerone are two naturally occurring compounds. What orbitals are used to form each indicated bond ... 

Although citrate has been excluded as the primary condensation product of pyruvate and oxalacetate, no direct evidence bearing upon the nature of this product has as yet been obtained. The participation of cfs-aconitic and isocitric acids is speculative. Nor is there any evidence supporting the hypothesis that pyruvate and oxalacetate condense to form a hypothetical intermediate oxalcitraconic acid which can be oxidatively decarboxylated to citric acid. Since citrate, aconitate and isocitrate are in equilibrium with each other, the participation of the last two substances as intermediates of carbohydrate oxidation would, on the surface, appear to be doubtful. Krebs, however, believes that the conversion of cis-aconitate to a-ketoglutarate occurs so rapidly in liver that equilibrium with citrate is not attained. 

Citric acid occurs naturally in a number of plant species and may be extracted from lemon juice, which contains 5-8% citric acid, or pineapple waste. Anhydrous citric acid may also be produced industrially by mycological fermentation of crude sugar solutions such as molasses, using strains of Aspergillus niger. Citric acid is purified by recrystallization the anhydrous form is obtained from a hot concentrated aqueous solution and the monohydrate from a cold concentrated aqueous solution. 

The reaction of calcium carbonate with HCl is closely related to the reaction you see when an Alka-Seltzer tablet is dropped into water. In this case sodium hydrogen carbonate, commonly called baking soda, reacts with a naturally occurring acid, citric acid (CgHsOy, page 120). 

Similar to fumaric acid, L-malic acid is also a naturally occurring four-carbon dicarboxyhc acid and an intermediate in the TCA cycle. It has been used in many food products, primarily as an acidulant. L-Malic acid is compatible with all sugars with low hygroscopicity and good solubihty. In addition, it has therapeutic value for the treatment of hyperammoemia and liver dysfunction and as a component for amino acid infusion. L-Malic acid has been the subject of interest because of its increased application in the food industry as a citric acid replacement and its potential use as a raw material for the manufacture of biodegradable polymers. 

---