By: Dr. Kasen Zhai1; M.Sc Richard Mudarra2.
More than a decade ago, the use of antibiotics as growth promoters was restricted in the European Union due to the severe consequences of bacterial resistance. This consequence was strengthened by the inappropriate, excessive, and continuous use of antibiotics in food formulation, as the main strategy for the control of pathogenic bacteria that affect livestock. After this restriction in 2006, the use of formaldehyde in feed was approved to guarantee its hygiene and safety without effects on productivity. The first application of formaldehyde was reported as an animal feed hygiene enhancer for mold control in the preservation of high-moisture corn (Spratt, 1985).
Formaldehyde played an important role in achieving a significant reduction in the use of antibiotics in animal feed in the European Union, guaranteeing feed hygiene safety and avoiding cross-contamination along the different axes that make up the food production supply chain. Previous studies have shown that the use of formaldehyde can effectively control pathogenic organisms such as Salmonella spp contained in food and water without affecting productivity (Carrique et al., 2007; Ricke, 2017).
However, the use of formaldehyde as a feed hygiene enhancer was banned in August 2018 due to human health risks according to the commission implementing regulation (EU)2018/183. Additionally, from a nutritional standpoint, formaldehyde has the ability to denature proteins and generate irreversible cross-linking between proteins, affecting normal digestion and utilization of protein sources.
Fortunately, while the use of formaldehyde was restricted, the European Food Safety Authority (EFSA) recommended formic acid as the only food safety enhancer allowed in all animal species according to commission implementing regulations (EU)2017/940.
Formic Acid Overview
Organic acids, such as formic acid, are characterized by a structure composed of hydrogen molecules, a carbon, and at least one other element, resulting in the presence of the functional carboxyl group (COOH). Formic acid (H2CO2 or HCOOH) is the first member of the aliphatic monobasic acid series. It is a colorless liquid, soluble in water and alcohol, with a pungent odor, with a molecular weight of 46.03 g/mol, a density of 1.22 g/cm3 at 20 ◦C, and a pKa of 3.75 (Luise et al., 2020).
Table 1. Physicochemical Properties of the Most Common Organic Acids.
|Organic Acid||Molar Mass (g/mol)||Density (g/mol)||pKa|
Adapted from (Luise et al., 2020).
The acidic effect of organic acids depends on their ability to donate protons in a common base, which is quantified by the dissociation constant (pKa; table 1). The pKa is the pH at which 50% of the acid is present in an undissociated form (COOH), and the other 50% is in a dissociated form (COO-). When a specific organic acid is dissociated, it releases the hydrogen molecules from their original structure. The lower the pKa value, the greater the acidic effect of the organic acid (Mroz, 2005). As shown in table 1, formic acid has the lowest pKa within the group of the most common organic acids, indicating its strength as an acidifying agent.
Mode of Action of Formic Acid.
The mechanism of action of organic acids is linked to their special characteristic of dissociation. The undissociated form of organic acids is more lipophilic and can easily diffuse into the cell wall of bacteria and molds.
Figure 1. Antimicrobial Effect of Formic Acid.
Formic acid passes through the cell wall of
the bacteria. Once inside, it begins to dissociate, releasing an anion (HCOO-) and a proton (H+) in the cytoplasm. The continuous accumulation of hydrogen molecules lowers the internal pH of the bacteria, disrupting enzymatic reactions (Figure 1). The bacterium activates a specific H+-ATP pump mechanism to bring the internal pH to a normal level. This continuous phenomenon, entails a high energy consumption by the bacteria, compromising its growth and, as a consequence, causing its death (Khan et al., 2022). At the same time, carboxylate anions can inhibit DNA and protein synthesis.
Based on their ability to penetrate the cell membrane of bacteria and destabilize their normal function to the point of death, organic acids are considered antimicrobial agents. To determine its antimicrobial capacity, the study of the minimum inhibitory concentration (MIC) is established. The MIC defines the in vitro levels of susceptibility or resistance of specific bacterial strains to a specific antimicrobial. The reliable evaluation of MIC has a significant impact on the choice of a therapeutic strategy, which depends on the efficiency of therapy against a specific infection (Kowalska and Dudek, 2021).
Scientific evidence reported by Strauss and Hayler (2001), showed that formic acid has the lowest minimum inhibitory concentration in the control of pathogenic bacteria compared to other common organic acids such as acetic acid and propionic acid (Table 2). Interestingly, formic acid has a MIC value of 0.10 and 0.15 for the control of bacteria such as Salmonella thymiruim and Escherichia coli, respectively, being 200% and 166% more efficient than propionic acid in the control of the same bacteria, consecutively.
|Adapted from (Strauss and Hayler, 2001)|
Table 2. Minimum Inhibitory Concentration (MIC) of Different Organic Acids.
In addition to its antimicrobial activity, formic acid improves nutrient utilization in animals because of its capacity on reducing the stomach pH, stimulating the enzymatic activity responsible for digestion; thus, improving growth performance. Additionally, due to its gastric pH-reducing effect, formic acid contributes to maintaining a low proliferation of opportunistic bacteria in the gastrointestinal tract, reducing the prevalence of digestive disorders.
Disadvantages of Formic Acid.
Although formic acid has shown to have a strong antimicrobial effect and modulate digestive activity, it has some disadvantages that limit its use.
Formic acid has a strong odor and causes skin, eye, and respiratory tract irritation (NJDH, 2010). Additionally, it exerts a severe corrosive effect (Sekine and Momoi, 1988), forcing strict requirements for transport equipment and storage equipment. The EFSA specified in its report EU (EU) 2017/940 that the maximum amount of formic acid used in the complete feed is 1%. Therefore, the large-scale use of formic acid in animal husbandry has been drastically compromised.
Due to the disadvantages that normal formic acid has, limiting its applicability safely and effectively, the animal nutritional industry needed to come up with new alternatives that supply the aforementioned functions of formic acid, but at the same time weaken the adverse effects on human health. Based on the above described, plus the application of technological advances, a molecule (Paraformic Acid) derived from formic acid, with safe effects, has been effectively developed.
General Concepts of Paraformic Acid.
Paraformic acid is a dimer of formic acid formed from two formic acid molecules through the polymerization process. Within its characteristics, paraformic acid is a brown liquid with a formic acid odor, without corrosive or irritant effect. The pH value of 1% paraformic acid solution is about 2.5. Paraformic acid releases two molecules of formic acid against bacteria and theoretically has the same mode of action that formic acid.
As part of preliminary studies of paraformic acid, its corrosive and irritant characteristics were evaluated.
Figure 2. Evaluation of the Corrosive and Irritant Effect of formic acid vs. Paraformic acid.
After the inclusion of metal clips in solutions of formic acid and paraformic acid for 30 minutes (Figure 2), a corrosive effect was found in clips immersed in normal formic acid, whereas the clips immersed in paraformic acid maintained their intact physical appearance without corrosive effect. Additionally, the irritant effect was evaluated, where New Zealand rabbits were used. Three treatments were applied, to which water, formic acid, and paraformic acid were applied to the skin. The level of irritation was evaluated on a scale of 0-9, finding high levels of irritation in those rabbits with normal formic acid (score 7), while there was no presence of skin irritation in those rabbits that had contact with paraformic acid or water. This evidence places paraformic acid as an innovative and safe additive without risks to the health of workers.
Paraformic acid has applicability in animal feed, in drinking water and also can be used as disinfectant (table 3).
Table 3. Recommended Dosage of Paraformic Acid (Megacid-F).
|Grower to Finisher||2-3|
|Sow||2-5||Lactating sow: 5Kg|
|Ruminate (TRM) or silage||5-6||4L /Ton silage|
|Drinking water||1L/1000L agua||5-6 hr/day|
Formic acid has shown to be an efficient bactericide, being able to easily replace formaldehyde and expanding its applicability in the industry without potential health risk, and at the same time offering additional qualities as acidifying and gastric enzyme activity stimulator.
Under the continuous demographic increase and its respective demand for food, and the limiting factors that restrict the use of formic acid, paraformic acid is currently positioned as a tool to maintain food safety and contribute to improve livestock efficiency.
Carrique, J., Bedford, S., and Davies, R. (2007). Organic acid and formaldehyde treatment of animal feeds to control Salmonella: efficacy and masking during culture. J Applied Microbiol. 103, 88–96. doi: 10.1111/j.1365-2672.2006. 03233.x
Khan, R. U., Naz, S., Raziq, F., Qudratullah, Q., Khan, N., Laudadio, V., Tufarelli, V., and Ragni, M. (2022). Prospects of organic acids as safe alternative to antibiotics in broiler chickens diet. Environmental Science and Pollution Research, 29(22), 32594–32604. https://doi.org/10.1007/ s11356- 022-19241-8
Kowalska, B., and Dudek, R. (2021). The minimum inhibitory concentration of antibiotics: Methods, interpretation, clinical relevance. Pathogens, 10(2), 1–21. https://doi.org/10.3390/pathogens10020165
Luise, D., Correa, F., Bosi, P., and Trevisi, P. (2020). A review of the effect of formic acid and its salts on the gastrointestinal microbiota and performance of pigs. Animals, 10(5). https://doi.org/10.3390/ani10050887
Mroz, Z. (2005). Organic Acids as Potential Alternatives to Antibiotic Growth Promoters for Pigs. Adv. Pork Prod, 162, 169–182.
NJDH. (2010). Hazardous substances fact sheet. Formic Acid. Technical Report. Available in: https://nj.gov/health/eoh/rtkweb/documents/fs/0948.pdf
Ricke, S. (2017). Feed Hygiene. In: Dewulf J, Van Immerseel F, editors. Biosecurity in Animal Production and Veterinary Medicine. Leuven: ACCO (2017). p. 144–76.
Sekine, I., and Momoi, K. (1988). Corrosion Behavior of Sus 329J1 Stainless Steel in Formic Acid Solution. Corrosion, 44(3), 136–142. https://doi.org/10.5006/1.3583915
Spratt, C. (1985). Effect of Mold Inhibitor Treated High Moisture Corn on Performance of Poultry. M.Sc. Thesis, University of Guelph.
Strauss, G. and Hayler, R. (2001). Effects of organic acids on microorganisms. Kraftfutter. 4. 147-151.
1Ph.D in Swine Nutrition. Numega Nutrition Pte. Ltd, Singapore. Email:Kasen@numega.com.cn
2 M.Sc. in Swine Nutrition and Production. Professor at Colleague of Agricultural Sciences/ University of Panamá. Email: email@example.com o firstname.lastname@example.org