Introduction
Natural acids (OA) are utilized in swine diet by way of water or feed particularly within the nursery section on account of their optimistic results on:
- gastrointestinal well being
- nutrient digestibility
- manufacturing efficiency
On the gastrointestinal degree, OAs can act as acidifiers, bactericides, and bacteriostatics, actions that rely primarily on the pKa, partition coefficient (LogP Kow), and molecular weight of every OA and the pH of the medium through which they’re discovered. Their impact will depend on the dose and the mix of OA used, the feed formulation, and the pig’s age- elements that make it troublesome to match between research.
OAs are additionally used as feed preservatives, because of their potential to inhibit the expansion of undesirable pathogenic micro organism, fungi, and yeasts in feed.
Chemical construction of natural acids
Biochemically, OAs are carboxylic acids characterised as natural compounds consisting of a fatty acid chain of variable size and a number of carboxyl teams (R-COOH) which might be the H+ donor supply.
OAs are weak acids, with totally different levels of solubility in water and with reversible response capability. We should differentiate OAs from inorganic acids, equivalent to phosphoric acid or hydrochloric acid because the latter are robust acids that dissociate utterly once they come into contact with water and have a excessive acidification capability however they can’t penetrate the inside of micro organism. Furthermore, their response is irreversible and their dealing with is sophisticated on account of their excessive corrosiveness. Desk 1 summarizes the principal OAs utilized in swine diet with their chemical system, pKa worth, molecular weight, and LogP Kow worth.
Desk 1. Chemical system, pKa worth, molecular weight, and LogP Kow of the principle natural acids utilized in swine diet (Dibner and Buttin, 2002; Zentek et al., 2011).
| Acid | Chemical system | pKa | Molecular weight, g/mol | LogP Kow |
|---|---|---|---|---|
| Brief Chain Fatty Acids (SCFA) | ||||
| Formic acid (1C) | HCOOH | 3.83 | 46.03 | -0.54 |
| Acetic acid (2C) | CH3COOH | 4.76 | 60.05 | -0.17 |
| Propionic acid (3C) | CH3CH2COOH | 4.88 | 74.08 | 0.33 |
| Butyric acid (4C) | CH3CH2CH2COOH | 4.82 | 88.12 | 0.80 |
| Acid | Chemical system | pKa | Molecular weight, g/mol | LogP Kow |
|---|---|---|---|---|
| Medium Chain Fatty Acids (MCFA) | ||||
| Caproic acid (6C) | CH3(CH2)4COOH | 4.88 | 172.26 | 1.92 |
| Caprylic acid (8C) | CH3(CH2)6COOH | 4.89 | 144.21 | 3.05 |
| Capric acid (10C) | CH3(CH2)8COOH | 4.89 | 172.26 | 4.09 |
| Lauric acid (12C) | CH3(CH2)10COOH | 5.13 | 200.32 | 4.60 |
| Acid | Chemical system | pKa | Molecular weight, g/mol | LogP Kow |
|---|---|---|---|---|
| Tricarboxylic acids | ||||
| Fumaric acid | COOHCH:CHCOOH | 3.02 4.76 |
116.07 | 0.46 |
| Citric acid | CH2(COOH)COH (COOH)CH2(COOH) |
3.13 4.76 6.49 |
192.14 | -1.70 |
| Acid | Chemical system | pKa | Molecular weight, g/mol | LogP Kow |
|---|---|---|---|---|
| Others | ||||
| Lactic acid | CH3CH(OH)COOH | 3.75 | 90.08 | -0.70 |
| Sorbic acid | CH3CH:CHCH:CHCOOH | 4.76 | 112.14 | 1.33 |
| Benzoic acid | C6H5COOH | 4.19 | 122.12 | 1.88 |
Predominant advantages of using natural acids in swine diet
- Promote gastrointestinal well being because of its bacteriostatic exercise by decreasing the pH of the medium via the discharge of its H+ ions and its bactericidal exercise in its undissociated type.
- Enhance digestibility and absorption of vitamins equivalent to protein and minerals, with excessive influence throughout the nursery section on account of acidification of abdomen contents and modulation of the microbiota.
- Preservative for uncooked supplies and feed on account of its potential to inhibit the expansion of undesirable pathogenic micro organism, fungi, and yeasts.
Mechanism of motion of natural acids within the digestive tract
Relying on the pH of the gastrointestinal medium and the pKa and LogP Kow of the OA, the OA may be in undissociated type (RCOOH, OA that retains all its chemical construction intact) or in dissociated type (RCOO- + H+, OA that has launched not less than one H+ ion to the medium).
An undissociated OA has a excessive diffusion capability via the membrane of the micro organism in the direction of its cytoplasm, the place the acid dissociates, altering the inner pH steadiness of the bacterial cytoplasm which can trigger the suppression of the exercise of its enzymatic methods and nutrient transport inflicting the lysis of the micro organism (Dibner and Buttin, 2002). Whereas a dissociated OA has acidification capability as a result of launch of H+ ions to the medium, inhibiting the expansion of acid-sensitive micro organism equivalent to Salmonella spp or E. coli and selling optimistic results on gastric and intestinal well being that we are going to focus on later.
OAs that may launch a single H+ equivalent to formic acid are referred to as monoprotic and OAs that may launch a couple of H+ equivalent to citric acid are referred to as polyprotic OAs. The chemical construction of the undissociated and dissociated types of formic acid, lactic acid, and propionic acid is depicted in Determine 1.
Determine 1. Chemical system of formic acid, lactic acid, and propionic acid of their undissociated and dissociated kinds.
However what determines whether or not a higher proportion of the acid is in dissociated or undissociated type on the gastrointestinal degree? It relies upon mainly on two elements: the pKa of the acid and the pH of the gastrointestinal surroundings.
The pKa of an OA (Desk 1) is the pH worth at which 50% of the acid stays dissociated and the remaining 50% undissociated. An OA has as many pKa values as there are carboxyl teams. Within the case of polyprotic OAs, their pKa worth will increase with every dissociation in order that the primary launch (pKa1) defines the acidification power of the actual OA. If the pH of the medium is decrease than the pKa of the OA, > 50% of the OA might be in undissociated type, whereas, if the pH of the medium is greater than the pKa of the OA, > 50% of the OA might be in dissociated type. Consequently, because the pH of the surroundings will get additional above or under the pKa worth of the OA, the proportion of dissociated or undissociated OA molecules will increase, respectively (Determine 2).
Determine 2. Proportion of dissociated/undissociated butyric acid, formic acid, and lactic acid molecules in accordance with the pH of the medium (Sieiro et al., 2013).
On the physiological degree, the decrease the pKa worth of OA, the higher the impact on gastric pH discount and the lesser the antimicrobial impact on the distal parts of the intestinal tract.
Two OAs with an analogous pKa and administered in the identical dose might have totally different bactericidal capacities on account of their molecular weight. For instance, when administered in the identical quantity, formic acid has a higher bactericidal impact than lactic acid since its molecular weight is decrease. It’s because, for an equal quantity, there might be extra molecules of formic acid than of lactic acid: in 1 kg of lactic acid there are 11.1 moles, whereas in 1 kg of formic acid there are 21.7 moles.
An OAs motion on microorganisms additionally will depend on the complexity of their outer cell membrane/wall. Medium-chain fatty acids (MCFA) have a powerful bactericidal motion on Gram-positive micro organism equivalent to Clostridium perfringens or Streptococcus spp, whereas short-chain fatty acids (SCFA) have a better bactericidal exercise on Gram-negative micro organism equivalent to E. Coli, Campylobacter jejuni, or Salmonella spp. That is as a result of octanol-water partition coefficient (LogP Kow, Desk 1) of every SCFA, which signifies whether or not an acid has a extra hydrophobic or hydrophilic character. Within the case of MCFAs, these have LogP Kow values higher than 1.0, indicating their lipophilic character that enables them to work together extra successfully with the cell membrane of Gram-positive micro organism, whereas the presence of lipopolysaccharides within the cell wall of Gram-negative micro organism confers resistance to MCFAs.
To improve the motion of OAs alongside the gastrointestinal tract, it’s attention-grabbing to work with mixtures of OAs with totally different properties. Chaveerach et al. (2002) noticed that the simultaneous mixture of propionic acid, acetic acid, and formic acid gives a better bactericidal energy in comparison with using these acids individually. Then again, Hanczakowska et al. (2013) concluded that the inclusion of a 0.5% 1:1 combination of propionic acid and formic acid and 0.2% capric acid positively impacts productive efficiency and will increase nutrient digestibility of post-weaning piglets via improved intestinal mucosal well being.
Some natural acids are used within the type of sodium, calcium, or potassium salts. In comparison with free natural acids, the dealing with of salts throughout feed manufacture is simpler on account of their decrease corrosiveness and they’re typically odorless on account of their strong type and decrease volatility. On the physiological degree, the salt is launched on the gastric degree, the undissociated OA reaching the intestinal degree the place it will possibly act both by acidifying the medium or by appearing as a bactericide relying on its pKa worth. Examples of OA salts are sodium formate (1k237), sodium propionate (1k281), and calcium propionate (1a282). The mixture of OA and OA salts with totally different pKa and LogP Kow values to realize an acidifying and bactericidal motion alongside the gastrointestinal tract is an efficient dietary software.
Natural acids and their salts can be utilized in swine diet in free or microencapsulated type. Microencapsulation prevents the acid from dissociating quickly within the abdomen, permitting the acids to behave within the extra distal components of the gut to behave as bacteriostatics or bactericides (Cho et al., 2014).
Within the subsequent factsheet the principle OAs utilized in swine diet and their mechanism of motion might be described along with a quick bibliographic compilation of scientific research on the impact of formic acid, lactic acid, and propionic acid on the gastrointestinal well being and productive efficiency of pigs.
