Benzoic acid: Good for the gut and performance
By using organic acids, such as benzoic acid, gut performance and performance can be given a boost. The effect is even greater if the product is encapsulated. In this article we highlight some of the trial data.
Organic acids (often referred to as volatile fatty acids, fatty acids, carboxylic acids or weak acids; Broom, 2015) are naturally-occurring carbon containing (hence organic) compounds with acidic properties. Due to their antimicrobial properties, organic acids are used for a long time as an effective means of reducing or controlling microbial contamination of feed and feed raw materials. Mold development is well controlled by propionic acid for instance; organic acids are also used to reduce pathogens like Salmonella in the food chain.
Effect of GI tract
The interest in the use of organic acids for farmed animals has increased with the possible replacement of antibiotic growth promoters (AGPs) and their mode of action in the digestive tract of pigs and poultry was investigated. In order to successfully traverse or inhabit the GI tract, microorganisms must survive extreme acid stress provided by the very low pH of the stomach environment (Broom, 2015). It must be noted that in the stomach, microorganisms faced hydrochloric acid which is a mineral, not an organic acid. To survive this extreme stress microorganisms have to maintain their internal, cytoplasmic pH near neutral (pH 7) as it represents the most appropriate conditions for their metabolic apparatus (e.g. enzymes). Microorganisms primarily attempt to maintain internal pH by minimizing membrane permeability to hydrogen ion (H+) and activating ion pumping mechanisms. These ion pumping mechanisms are energetically expensive and if the exposure to the acidic stress lasts too long other key metabolisms are disrupted, bacteria growth is inhibited and cell death can occur.
The pKa value
An essential characteristic of organic acids is the pKa value; organic acids are composed of a carbon chain which is an anion, negatively charged, and of a hydrogen ion (H+). When both are associated the acid is uncharged and is able to diffuse freely across the microbial cell membrane. The pKa value is the environmental pH where half of the organic acid content is dissociated and half stays undissociated. As pKa values of organic acids are generally lower than 5, when the undissociated form has entered a bacteria cell, pH of the cell cytoplasm being near 7, the acid dissociates and the resulting H+ ions acidify the cytoplasm, stressing the pH regulatory mechanisms of the cell as described above.
At the difference of mineral acids like hydrochloric acid, the anion portion of the organic acid accumulates in the cell causing other damages. When the pKa is higher than the medium pH, more of the acid is dissociated and less able to penetrate the microbial cell membrane. Thus, within the gastrointestinal tract, a given concentration of an organic acid is likely to have a greater antimicrobial effect in the lower pH regions than in the higher pH ones, and this is an important consideration for organic acid application and product development. In any case, the slight modifications of the pH in different parts of the gastrointestinal tract, when they are observed, determine the efficacy of organic acids (Broom, 2015). One hypothesis is that modifications of the local pH could be due to the lactic acid production by lactic bacteria, stimulated by the control of more acid susceptible pathogenic microorganisms.
Figure 1 – Minimum inhibitory concentrations (MIC in ppm) of benzoic acid against microorganisms isolated from animals.
Which organic acid to choose?
For feed decontamination, formic acid is given as the best antimicrobial organic acid. It is not the best choice for an intestinal microorganism target. The pKa value of formic acid is lower than 4; it is a small molecule and quickly metabolised. Benzoic acid has a pKa value of 4.2 and the phenolic part is an efficient damaging agent for the bacteria cell. Benzoic acid is a solid molecule and also less corrosive and safer to handle compared to formic, propionic or lactic acids which are liquids. Figure 1 shows the minimum inhibitory concentrations of benzoic acid on different bacteria (not published data). As it is the general case for organic acids, gram-negative (i.e. E. coli, Salmonella) are much more inhibited than gram-positive bacteria.
Amongst the gram-positive bacteria, the “beneficial bacteria” (i.e. Lactobacillus spp.) is less sensitive to the antibacterial effects of benzoic acid. It has already been reported that benzoic acid plays an important role lowering numbers of many pathogenic bacteria as Campylobacter jejuni, Escherichia coli, Listeria monocytogenes and Salmonella enterica (Giannenas et al, 2010).
Giannenas et al (2014) reported that 0.03 and 0.1% (300 and 1000 ppm) of benzoic acid in turkey (+5% of weight gain and less 6.5% for FCR in poults receiving 300 ppm of benzoic acid at 56 days of age) and broiler diets improved the performance of birds compared to non supplemented control birds. Coliforms populations were reduced in bird caeca while lactic acid bacteria increased. Olukosi and Dono (2014) observed significant improvement of villus height, villus width, crypt depth and crypt width in the jejunum of broilers receiving 2000 ppm of benzoic acid in their feed.
Clear negative effects of high dosage of organic acids were observed in poultry. For benzoic acid, Giannenas et al (2014) reported that birds receiving the diet supplemented at the lowest dosage (300 ppm) of benzoic acid performed better than birds receiving 1000 ppm. Josefiak et al (2010) reported that 0.2% of benzoic acid depressed performance in broilers, while 0.1% improved bird performance. One can conclude than it is not necessary to use high dosages of acids to improve the performance of poultry.
Despite benefits of organic acids, a major constraint associated with organic acids is their rapid metabolism and absorption in the proximal parts of gastrointestinal tract, which results in low concentration, no effect, in the distal parts. Yousaf et al (2016) measured the acid concentrations in the crop, jejunum, ileum and caeca of broilers receiving from day old to 35 days of age, a feed supplemented with 821.6 mmol/kg of benzoic acid. Compared to negative control birds, benzoic acid concentrations were higher (multiplied by 2 to 10 folds) in treated birds, but the acid was essentially released in the crop.
Target release by encapsulation
To reach antimicrobial concentrations in the distal intestine of poultry, it would be necessary to increase the level of organic acids dramatically in the feed, causing decreased feed intakes. Therefore different attempts have been made to protect organic acids from dissociation and absorption in the proximal intestine by microencapsulating the active compounds in a matrix which would lead to releasing the active compounds in the distal parts of the gut (Yousaf et al, 2016). Generally encapsulation is done with hydrogenated vegetable oils and progressive digestion by lipases released slowly by the acid. Yousaf et al (2016) showed that encapsulated benzoic acid was able to significantly increase lactic acid bacteria in the caeca and reduce coliforms.
Figure 2 – Release kinetic of benzoic acid.
Figure 2 shows the protective effects of microencapsulated benzoic acid release under simulated conditions of gastric and intestinal digestion in a poultry in vitro model (MiXscience internal results, not published data). Vectorization using the microencapsulation of active ingredients in a fatty acid encapsulation appears as an effective solution to protect organic acids from dissociation and absorption in the proximal intestine. Vectorization is a process of choosing the best ingredients – taking into account the possible synergies between them – and associating them with carriers and, if needed, encapsulation agents. The aim is to ensure optimal efficiency of the selected ingredients, by bringing them at the right place, at the right time. As shown in Figure 2, the aBcid encapsulation allows limiting the “gastric” release at 35% and then a progressive release all along the intestine. This observed gastric bypass is particularly interesting compared to another encapsulated benzoic acid on the market (64% of acid released). Positive effects on poultry performance were already clearly demonstrated and we can expect that new future technologies of vectorization could contribute to improving the performances even more.
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