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An organic acid is an organic compound with properties. The most common organic acids are the , whose acidity is associated with their carboxyl group –COOH. , containing the group –SO2OH, are relatively stronger acids. Alcohols, with hydroxyl group, can act as acids but they are usually very weak. The relative stability of the conjugate base of the acid determines its acidity. Other groups can also confer acidity, usually weakly: the thiol group –SH, the enol group, and the phenol group. In biological systems, organic compounds containing these groups are generally referred to as organic acids.
A few common examples include:
On the other hand, most organic acids are very soluble in organic solvents. p-Toluenesulfonic acid is a comparatively strong acid used in organic chemistry often because it is able to dissolve in the organic reaction solvent.
Exceptions to these solubility characteristics exist in the presence of other substituents that affect the polarity of the compound.
The of organic acids such as citric acid and Lactic acid are often used in biologically compatible .
Citric and oxalic acids are used as rust removal. As acids, they can dissolve the iron oxides, but without damaging the base metal as do stronger mineral acids. In the dissociated form, they may be able to chelate the metal ions, helping to speed removal.
Biological systems create many more complex organic acids such as lactic acid, citric acid, and D-glucuronic acids that contain hydroxyl or . Human blood and urine contain these plus organic acid degradation products of amino acids, neurotransmitters, and intestinal bacterial action on food components. Examples of these categories are alpha-ketoisocaproic, vanilmandelic, and D-lactic acids, derived from catabolism of leucine and epinephrine (adrenaline) by human tissues and catabolism of dietary carbohydrate by intestinal bacteria, respectively. Organic acids (C1–C7) are widely distributed in nature as normal constituents of plants or animal tissues. They are also formed through microbial fermentation of carbohydrates mainly in the large intestine. They are sometimes found in their sodium, potassium, or calcium salts, or even stronger double salts.
Upon passive diffusion of organic acids into the bacteria, where the pH is near or above neutrality, the acids will dissociate and raise the bacteria internal pH, leading to situations that will not impair nor stop the growth of bacteria. On the other hand, the anionic part of the organic acids that can escape the bacteria in its dissociated form will accumulate within the bacteria and disrupt few metabolic functions, leading to osmotic pressure increase, incompatible with the survival of the bacteria.
It has been well demonstrated that the state of the organic acids (undissociated or dissociated) is not important to define their capacity to inhibit the growth of bacteria, compared to undissociated acids.
Lactic acid and its salts sodium lactate and potassium lactate are widely used as in food products, in particular, dairy and poultry such as ham and sausages.Applications for lactic acid.http://www.purac.com/purac_com/67cbf5490d83dc478dafbd96cab841b1.php
Organic acids added to feeds should be protected to avoid their dissociation in the crop and in the intestine (high pH segments) and reach far into the gastrointestinal tract, where the bulk of the bacteria population is located.
From the use of organic acids in poultry and pigs, one can expect an improvement in performance similar to or better than that of antibiotic growth promoters, without the public health concern, a preventive effect on the intestinal problems like necrotic enteritis in chickens and Escherichia coli infection in young pigs. Also one can expect a reduction of the carrier state for Salmonella species and Campylobacter species.
Barbero-López and colleagues tested at the University of Eastern Finland the potential use of three organic acids, acetic, formic and propionic acids, in wood preservation. They showed a high antifungal potential against the decaying fungi tested (brown rotting fungi Coniophora puteana, Rhodonia placenta and Gloeophyllum trabeum; White rotting fungus Trametes versicolor) in Petri dish. However, when they treated wood with organic acids, the acids leached out from wood and did not prevent degradation. Additionally, the organic acids' acidity may have caused chemical degradation on wood. Additionally, in a more recent study, the ecotoxicity of several natural wood preservatives was compared, and the results indicated a very low toxicity of propionic acid.
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