Organic Acids - A Review

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Due to the vast expansion of poultry industry challenges also increases. One of them is the control of microbial population which is done by excessive use of therapeutics antibiotics and AGP’s. The indiscriminate use of these products results in the emergence of antibiotic resistance. Apart from resistance it also leads to public health concern. Due to this EU has banned the use of AGP’s in 2006. After that, researchers found different ways to combat the problem of microbial control. Among these is the use of organic acids, probiotics, prebiotics, Essential oils, bacteriophages etc. among these organic acids have gained much attention in this regard because they have antimicrobial activity against pathogenic bacteria and improves the nutrient digestion and absorption by several mechanisms.

 

What is organic acid

An organic acid is a carboxylic acid including fatty acid having the formula R-COOH with acidic properties.

 

Most commonly used organic acid are short chain fatty acid e.g. formic acid, propionic acid, butyric acid, acetic acid, citric acid and malic acid which is a dicarboxylic acid. These all are usually weak organic acids which when dissolved in water changed into their hydrogen and hydroxyl ion respectively. The working and mode of action of these acids are dependent upon their PH and Pka value. Pka is a value at which 50% of acid is present in dissociated form. Only in its undissociated form an organic acid crosses the cell wall of bacteria and perform its antimicrobial activity. This means that these organic acids have much pronounced activity in acidic environment e.g. in the stomach and reduced activity in alkaline environment e.g. in the small intestine.

 

Accordingly, organic acids with a high pKa value are weaker acids and therefore more effective preservatives for feed, as, being present in the feedstuff with a higher proportion of their undissociated form, can defend feed from fungi and microbes. Therefore, the lower the pKa of the like formic and lactic acid are used for improving digestibility process in animals. organic acid (the higher proportion of dissociated form) the greater is its effect on the reduction of stomach pH and the lower its antimicrobial effect in the more distal portions during its transit through the digestive tract. A strong acid (with low pKa) will acidify the feed and the stomach, but will not have strong direct effects on the microflora in the intestine. This is the reason why acid like propionic acid with higher Pka value is used as preservative of feed, while acid with lower Pka

 

Mode of action

The undissociated form crosses the lipid cell wall of the microbe. The higher cellular PH causes the dissociation of acid releasing its H+ ions which lower the PH of microbial cell. The lower PH has a deleterious effect on various metabolic processes including DNA replication. Microbial cell uses energy to counteract this PH lowering effect which leads to exhaustion and eventual death of microbe. The remaining anions(-COOH) also have negative effects on cell critical metabolic processes.

 

 

Benefits of using organic acid in animal nutrition

Killing of microbes especially gram negative (Salmonella, E. coli) in drinking water and in the intestine leads to better utilization and absorption of feed which results in better weight gain and FCR. The PH lowering effect hampers the growth of pathogenic microbes.

Prevent biofilm formation in the drinking systems thus minimize the pathogen load in water.

Increase the digestibility of nutrients especially proteins by its pronounced PH reducing effect in the stomach which enhance the release of pepsin which is a protein degrading enzyme.

Increase the pancreatic secretions result in better digestion and metabolism of fat.

Delay the gastric emptying time of feed result in better nutrient absorption.

They serve as intermediary substrates (butyric acid, citric acid) in the different cycles of metabolism thus act as a direct energy source for the bird. Several research trials have shown the positive effect of butyric acid in reducing the Salmonella population in the intestine presumably by inhibiting the synthesis of pathogenic factors by salmonella. Butyric acid is an intermediary metabolite in the energy cycle in enterocytes thus it maintains the performance and integrity of the enterocytes.

Reduce the incidence of diarrhea and subclinical enteritis.

Enhance the absorption of minerals (P, Cu, Zn)

Alternatives to AGPs to reduce medication cost.

 

NEW STRATEGIES FOR organic acids have been developed for its better functioning in the intestine. These strategies include encapsulation of organic acid. The encapsulation process ensures the targeted release of acid in the small and large intestine where major pathogenic load of microbes are present. Another strategy is the use of glyceride of acid. In this process, organic acid is attached (esterified) with glycerol. This combination protects the acid from degradation by the stomach PH. Once these glycerides are reached in the small intestine lipase enzyme breaks the bond and acid is released.

Use of a combination of the organic acid is another strategy used. Because as stated earlier different organic acids have different pka values so they behave differently along the tract. The purpose of using combination is to maximize the effects along the tract. Use of salts of organic acids e.g. potassium formate is also common. Use of salt of acid reduces the bitterness and corrosiveness of acid.

 

Conclusion

Organic acids have potential to use as an alternative to AGPs. They reduce the medication cost improves animal performance and production parameters, have a broader spectrum of activity. Use of technology further enhances their effectiveness.

 

References:

H. M. A. Hassan*, M. A. (October 2010). Effect of Using Organic Acids to Substitute Antibiotic Growth Promoters on Performance and Intestinal Microflora of Broilers. Asian-Aust. J. Anim. Sci. Vol. 23, No. 10, 1348 - 1353.

Ján Kopecký, C. H. (2012). Effect of Organic Acids Supplement on Performance of Broiler Chickens, Slovak University of Agriculture in Nitra, Faculty of Agrobiology and Food Resources, Department of Poultry Science and Small Animal Husbandry, 949 76-Nitra, Tr. A. Hlinku, 2, Slovak. Animal Sciences and Biotechnologies, 51-54.

María Alejandra Pérez-Alvaradoa, J. C. (n.d.). Organic Acids, with emphasis on Benzoic Acid, to rationalize the use of therapeutic antibiotics.

P. Chaveerach, *. D. (2004). Effect of Organic Acids in Drinking Water for Young Broilers on Campylobacter Infection, Volatile Fatty Acid Production, Gut Microflora and Histological Cell Changes. Poultry Science, 330-334.

S.N.S Silva, A. P. (2016). in vitro efficacy of four sodium salt of organic acids against E.coli isolated from poultry outbreaks in Sri Lanka. The World Poultry Science Association, 16-18.

 
Author/s
Dr. Mohammad Akram Dr. Mohammad Akram
Consultant Microbiologist
August 7, 2017
Dear Authors,
No doubt acidic pH is not suitable for the growth of bacteria, therefore using organic acid shall be helpful to reduce the bacterial problems.
Unfortunately, lower pH is suitable for the growth of fungi. Therefore use of organic acid cuold enhance the growth of fungi and promote the fungal infection.
I shall be greatful to know your valuable comments of this issue.
Regards
Dr. M. Akram, Consultant Microbiologist, Micro Laboratories, Karachi, Pakistan
2
Reply
Olivier Desrues Olivier Desrues
PhD, University of Copenhagen
Silvateam S.p.a Silvateam S.p.a
Piemonte, Italy
August 7, 2017

You said it kills microbes, what about bacterial adaptation? Perhaps you should take it into account in your strategy?

2
Reply
August 7, 2017

Thank you, sir Akram, for your point can you send me some published data to support your argument because according to my limited knowledge organic acids does work as mold inhibitors.
Thanks.
my email id is
dr.usama391@gmail.com

0
Reply
August 7, 2017

Thank you, Olivier, for your comment. about your question adaptation is negligible according to my knowledge.

0
Reply
ADDCON ADDCON
Porsgrunn, Germany
August 7, 2017
Dear Dr. Muhammad Akram, You raised a very interesting point. The fungi growth is promoted when dysbiosis takes place which occur more often in case of AGP supplementation. The OA supplementation promotes Eubiosis which naturally keeps a check on fungi growth.
2
Reply
ADDCON ADDCON
Porsgrunn, Germany
August 7, 2017
Dear Olivier, it is just a hypothesis and no research at least to my knowledge has been published indicating the development of resistant strains of bacteria against OA.
0
Reply
star Mirza M H Mushtaq Mirza M H Mushtaq
PostDoc in Poultry Nutrition
August 8, 2017

Pka value of formic acid is a big question on its release in later part of the intestine. And to what extent it reduces pH in different parts of GIT? Also what kind of substances were used before AGP era? Organic acids? 
Also, think of other organic acids... and other substances.. having additive effects with organic acids.

0
Reply
star Christoph Hutter Christoph Hutter
Poultry farmer
ADDCON ADDCON
Porsgrunn, Germany
August 8, 2017

Hi all,
Pka value on formic is to my knowledge 3,75
Why it should not be known.
If you feed formic acid pure nearly nothing will arrive in the latter part of the destine.
The ph value is not the big difference in the action in the destine you will come down 0.3 - 0.5 ph and it helps more for better secretion of destine juices.
Resistance is always a discussion but against the action of an acid it is not easy to be resistant.

2
Reply
Joshua Jendza Joshua Jendza
Animal Nutritionist
August 9, 2017
The pKa of formic acid is known (3.75 as indicated by someone else). As for how this affects dissociation, that depends on the pH of the surrounding environment. The degree of association/disassociation between the cation and anion is dependent on the pH of the solution.

Formic acid added to feed with a pH of 6-7 will completely disassociate. However, once that acidified feed is consumed and further acidified by the HCl in the proventriculous of the bird, it will reassociate by taking up H+ ions released by the HCl produced by the birds. This is because the association/disassociation of acids is reversible.

Generally the pH of the proventriculous has a pH between 2 to 4, meaning that formic acid will be between 2 and 100% disassociated, depending on the specific pH of the microenvironment within the proventriculous. Later on, when the digesta flows into the more alkaline intestine, the dissociation degree will be 100% (any pH at 3.8 or above). However, this is the average pH of the digesta. Within the gut there are acidic microenvironments along the brush boarder membrane that are essential to proper function of many nutrient transporters (any based on an inwardly directed proton gradient), so even in the ostensibly neutral pH intestine, there exist micro environments where some formate would be able to reassociate with H+ and regenerate formic acid from formate.
5
Reply
ADDCON ADDCON
Porsgrunn, Germany
August 9, 2017
I agree with Joshua Jendza as far as the questions of @Haroon are concerned, I would suggest you to look at diformate molecule and lot of fog will be cleared. Also, the other organic acids do have bacteriocidal and basteriostatic properties but one has to see the MIC especially when choosing a product that contain a mix of different organic acids. From that angle, in those products, none of the organic acid will be in sufficient quantity to effectively acidify the gut. Diformate molecule has the ability to go down the intestine as shown by high percentage recovery in distal segments of the intestine.
2
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