Organic acid

An organic acid is an organic compound with acidic properties. The most common organic acids are carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, which contain the group –SO₂OH, are relatively stronger acids. Alcohols, with –OH, can act as acids, but are generally 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 –SH group, the enol group, and the phenol group. In biological systems, organic compounds containing these groups are generally called organic acids.

Features

In general, organic acids are weak acids and do not fully dissociate in water, while strong mineral acids do. Organic acids of low molecular mass, such as formic and lactic acids, are miscible with water, but organic acids of higher molecular mass, such as benzoic acid, are insoluble in molecular (neutral) form.

On the other hand, most organic acids are highly soluble in organic solvents. p -Toluenesulfonic acid is a comparatively strong acid often used in organic chemistry because it is capable of dissolving in the organic reaction solvent.

Exceptions to these solubility characteristics exist in the presence of other substituents that affect the polarity of the compound.

Applications

Applications

Conjugate bases of organic acids such as citrate and lactate are often used in biologically compatible buffer solutions.

Citric and oxalic acids are used for rust removal. As acids, they can dissolve iron oxides, but without damaging the base metal as stronger mineral acids do. In the dissociated form, they may be able to chelate metal ions, helping to speed up elimination.

Biological systems create many more complex organic acids, such as L-lactic, citric, and D-glucuronic acids that contain hydroxyl or carboxyl groups. Human blood and urine contain these organic acid breakdown products of amino acids, neurotransmitters, and intestinal bacterial action on food components. Examples of these categories are alpha-ketoisocaproic, vanillmandelic, and D-lactic acids, derived from the catabolism of L-leucine and epinephrine (adrenaline) by human tissues and the catabolism of dietary carbohydrates by intestinal bacteria, respectively.

The general structure of a few weak organic acids. From left to right: phenol, enol, alcohol, tiol. The acid hydrogen in each molecule is red.

The general structure of a few organic acids. From left to right: carboxylic acid, sulfonic acid. The acid hydrogen in each molecule is red.

Food Application

Organic acids are used in food preservation due to their effects on bacteria. The fundamental basic principle about the mode of action of organic acids on bacteria is that undissociated (non-ionized) organic acids can penetrate the cell wall of bacteria and disrupt the normal physiology of certain types of bacteria that we call pH sensitive, which means that they cannot tolerate a wide internal and external pH gradient. These bacteria include Escherichia coli, Salmonella spp., C. perfringens, Listeria monocytogenes and Campylobacter.

Following passive diffusion of organic acids into bacteria, where the pH is close to or above neutrality, the acids will dissociate and lower the internal pH of the bacteria, leading to conditions that will affect or stop the growth of bacteria. On the other hand, the anionic part of the organic acids that cannot escape from the bacteria in their dissociated form will accumulate inside the bacteria and disrupt many metabolic functions, leading to an increase in osmotic pressure, incompatible with the survival of the bacteria. the bacteria.

It has been well demonstrated that the state of organic acids (undissociated or undissociated) is extremely important in defining their ability to inhibit bacterial growth, compared to undissociated acids.

Lactic acid and its salts, sodium lactate and potassium lactate are widely used as antimicrobials in food products, particularly meat and poultry such as ham and sausage.

Application in animal nutrition and feeding

Organic acids have been used successfully in swine production for over 25 years. Although less research has been done on poultry, organic acids have also been found to be effective in poultry production.

Organic acids (C₁-C₇) are widely distributed in nature as normal constituents of plant or animal tissues. They are also formed through microbial fermentation of carbohydrates, primarily in the large intestine. They are sometimes found in their sodium, potassium, or calcium salts or even stronger double salts.

Organic acids added to food must be protected to prevent their dissociation in the culture and in the intestine (high pH segments) and reach the gastrointestinal tract, where most of the bacterial population is found.

From the use of organic acids in poultry and pigs, a performance improvement similar or better than that of antibiotic growth promoters can be expected, without the public health concern, a preventive effect on intestinal problems such as necrotic enteritis in chickens or infection in young pigs with Escherichia coli. A reduction in carrier status can also be expected for Salmonella and Campylobacter species.

Examples

Some common examples include:

• Lactic acid
• Acetic acid
• Formal acid
• Citric acid
• Oxalic acid
• Uric acid
• Maxic acid

Further reading

• Dibner, J. J.; Butin, P. (2002). «Use of organic acids as a model to study the impact of gut microflora on nutrition and metabolism». J. Appl. Poultry Res. 11 (4): 453-463. Archived from the original on March 6, 2011. Consultation on May 18, 2019.
• Patanen, K. H.; Mroz, Z. (1999). «Organic acids for preservation». In Block, S. S., ed. Disinfection, sterilization & preservation (5th edition). Philadelphia: Lea Febiger. ISBN 0-683-30740-1. Patanen, K. H.; Mroz, Z. (1999). «Organic acids for preservation». In Block, S. S., ed. Disinfection, sterilization & preservation (5th edition). Philadelphia: Lea Febiger. ISBN 0-683-30740-1. Patanen, K. H.; Mroz, Z. (1999). «Organic acids for preservation». In Block, S. S., ed. Disinfection, sterilization & preservation (5th edition). Philadelphia: Lea Febiger. ISBN 0-683-30740-1.
• Brul, S.; Coote, P. (1999). «Preservative agents in foods, mode of action and microbial resistance mechnismes». International Journal of Food Microbiology 50 (1–2): 1-17. PMID 10488839.