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Anorganic acid is anorganic compound withacidic properties. The most common organic acids are thecarboxylic acids, whose acidity is associated with theircarboxyl group –COOH.Sulfonic acids, containing the group –SO2OH, are relatively stronger acids. Alcohols, with–OH, can act as acids but they are usually very weak. The relative stability of theconjugate base of the acid determines its acidity. Other groups can also confer acidity, usually weakly: thethiol group –SH, theenol group, and thephenol group. In biological systems, organic compounds containing these groups are generally referred to as organic acids.
A few common examples include:
In general, organic acids are weak acids and do not dissociate completely in water, whereas the strongmineral acids do. Lower molecular mass organic acids such asformic andlactic acids aremiscible in water, but higher molecular mass organic acids, such asbenzoic acid, are insoluble in molecular (neutral) form.
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.
Simple organic acids likeformic oracetic acids are used for oil and gas well stimulation treatments. These organic acids are much less reactive with metals than are strong mineral acids likehydrochloric acid (HCl) or mixtures of HCl andhydrofluoric acid (HF). For this reason, organic acids are used at high temperatures or when long contact times between acid and pipe are needed.[citation needed]
Theconjugate bases of organic acids such ascitrate andlactate are often used in biologically compatiblebuffer solutions.
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 tochelate the metal ions, helping to speed removal.
Biological systems create many more complex organic acids such asL-lactic,citric, andD-glucuronic acids that containhydroxyl orcarboxyl groups. Human blood and urine contain these plus organic acid degradation products ofamino acids,neurotransmitters, and intestinal bacterial action on food components. Examples of these categories are alpha-ketoisocaproic, vanilmandelic, andD-lactic acids, derived fromcatabolism ofL-leucine andepinephrine (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 calciumsalts, or even stronger double salts.
Organic acids are used infood preservation because of their effects on bacteria. The key basic principle on the mode of action of organic acids on bacteria is that non-dissociated (non-ionized) organic acids can penetrate the bacteria cell wall and disrupt the normal physiology of certain types of bacteria that we callpH-sensitive, meaning that they cannot tolerate a wide internal and external pH gradient. Among those bacteria areEscherichia coli,Salmonella spp.,C. perfringens,Listeria monocytogenes, andCampylobacter species.
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 saltssodium lactate andpotassium lactate are widely used asantimicrobials in food products, in particular, dairy and poultry such as ham and sausages.[1]
Organic acids have been used successfully in pig production for more than 25 years. Although less research has been done in poultry, organic acids have also been found to be effective in poultry production.
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 andEscherichia coli infection in young pigs. Also one can expect a reduction of the carrier state forSalmonella species andCampylobacter species.
In addition to the end uses previously seen, organic acids have been tested for the following applications:
Barbero-López and colleagues[2] 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 fungiConiophora puteana,Rhodonia placenta andGloeophyllum trabeum; White rotting fungusTrametes 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.[3]
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