What is Gallic Acid used for

Gallic acid (gallic acid) is a natural organic phenolic acid,which has the properties of polyphenols and acids,and is the main active component of many plants.Leaves,eucalyptus,pomegranate peel and other plants.As an organic phenolic acid,gallic acid has strong reducibility and easily reacts with proteins,enzymes and alkaloids,and exerts biological functions such as antibacterial,antioxidant and anti-inflammatory.Anti-free radical and other properties.At present,plant-derived feed additives with gallic acid as the main active ingredient have achieved certain results in regulating animal growth and health and reducing the use of antibiotics in livestock and poultry production. 

1. Molecular structure and metabolic pathways of gallic acid

1.1 Molecular structure of gallic acid

Gallic acid,also known as 3, 4, 5-trihydroxybenzoic acid and gallic acid,has a molecular formula of C6H2(OH)3COOH and contains 3 phenolic hydroxyl groups and 1 carboxyl group.Gallic acid can be prepared under the catalytic conditions of acid, alkali,enzyme,etc.The extract is white or light brown needle-like or prismatic crystal,which often exists in the state of monohydrate,and the relative molecular mass is 170.12.

 1.2 Metabolic pathway of gallic acid

The metabolism of gallic acid in animals is basically the same as that of polyphenolic compounds.After gallic acid enters the body,it is prone to decarboxylation and methylation reactions under the action of various enzymes of intestinal bacteria in the body,and the products mainly exist in the form of methyl sulfation,glucuronidation and sulfation.Part of the metabolites is transported from the intestinal segment to the serosa and absorbed into the blood circulation by glucuronyl transferase,etc., and part of the glycoside is passively diffused and absorbed in the small intestine.Other flavonoid metabolites are excreted into bile via the enterohepatic circulation and reabsorbed from the intestine. 

2 Biological functions of gallic acid

2.1 Bacteriostatic effect

A large number of in vitro studies have confirmed that gallic acid has significant antibacterial activity.Gallic acid has a significant inhibitory effect on 6 common food-borne pathogenic bacteria and spoilage bacteria (Staphylococcus aureus, Bacillus subtilis,Bacillus cereus,Bacillus megaterium,Listeria monocytogenes,Escherichia coli).Listeria monocytogenes had the best inhibitory effect,and 4 mg/mL gallic acid had different effects on the growth curves of the above bacteria.In addition,gallic acid also has a certain growth inhibitory effect on pathogenic bacteria such as Salmonella,Pseudomonas aeruginosa, Helicobacter pylori,which are common in vitro.Compared with various antibiotics,the bacteriostatic effect of gallic acid with a concentration of 0.09 g/mL on Staphylococcus aureus,Escherichia coli and Salmonella was slightly lower than that of gentamicin with a concentration of 0.1 g/mL. Above 0.1 g/mL of acetylspiramycin,the antibacterial activity of gallic acid is slightly lower than that of gentamicin,but higher than that of acetylspiramycin; Staphylococcus aureus, etc.) have a significant impact on the biofilm integrity and permeability,which provides a new solution to problems such as drug resistance and drug residues caused by the abuse of antibiotics in animal husbandry.

The antibacterial mechanism of gallic acid mainly includes the following two aspects: 

1.Destruction of the structural integrity of bacteria.Gallic acid causes irreversible changes in the properties of the membrane (charge,intracellular and extracellular permeability and physical and chemical properties) by changing the hydrophobicity of the cell surface,reducing the negative charge and local rupture of the cell membrane.The content leaks,the bacteria show obvious shrinkage shape,the volume shrinks and becomes agglomerated,and the structure and function are damaged to varying degrees,which affects the growth and reproduction of bacteria.

2.Inhibits the formation of bacterial biofilms in vitro.Gallic acid contains phenolic hydroxyl and carboxyl structures,has strong reducing properties,and is easy to interact with proteins and enzymes,thereby changing the metabolic activities of bacteria.In an in vitro metabolic model of anaerobic cultured mouse intestinal flora,gallic acid is prone to decarboxylation and methylation reactions under the action of intestinal bacterial enzymes,resulting in changes in bacterial cell membrane morphology.

2.2 Antioxidant effect

Gallic acid plays a significant role in scavenging free radicals,effectively removing excess reactive oxygen species produced by the body,and protecting and inhibiting oxidative damage to proteins,lipids and DNA.Tests show that,compared with vitamin C (VC),gallic acid has a significant scavenging effect on 2,2-biphenyl-1-picrylhydrazine (DPPH) free radicals and hydroxyl radicals within a certain concentration range,and the scavenging ability Significantly higher than VC; the inhibitory effect on lipid peroxidation is also better than that of VC,and the scavenging ability of nitric oxide (NO) is only slightly lower than that of VC. In the mitochondrial antioxidant assay,gallic acid can maintain the potential and osmotic pressure inside and outside the mitochondrial membrane,inhibit and remove reactive oxygen species generated during oxidative phosphorylation,protect mitochondrial DNA (mtDNA) and reduce protein carbonylation.The molecular structure of gallic acid has aromatic rings and hydroxyl groups,which can improve the efficiency of electron transfer through resonance,thereby rapidly neutralizing free radicals.Studies have shown that gallic acid often does not directly interact with peroxides in the body,but exerts its anti-free radical properties through its strong affinity for free radicals.Therefore,it is inferred that the mechanism of gallic acid exerting its antioxidant effect may be the hydrogen extraction reaction between phenolic hydroxyl groups and free radicals.It has also been reported that gallic acid exerts antioxidant properties by effectively down-regulating reactive oxygen species metabolism and maintaining high levels of reduced glutathione (GSH)/oxidized glutathione (GSSG).

2.3 Anti-inflammatory effect

Gallic acid can inhibit the expression and activity of a variety of inflammatory factors,thereby exerting anti-inflammatory effects.In the mouse foot swelling model,gallic acid can enhance the phagocytic activity of polymorphonuclear leukocytes (PMNs) in vitro,further inhibit the activity of myeloperoxidase through PMNs,and the anti-inflammatory activity of gallic acid is dose-dependent.RAW264.7 macrophages were stimulated in vitro with lipopolysaccharide (LPS) and then intervened with gallic acid, and it was found that the secretion of intracellular tumor necrosis factor-¦Á (TNF-¦Á), interleukin (IL)-6, and IL-1 was significantly increased.The expression of Toll-like receptor 4 (TLR4) on the cell membrane was also decreased, and the phosphorylation level of inhibitory protein of nuclear factor-¦ÊB (NF-¦ÊB) (I¦ÊB) was significantly reduced,and the activation of NF-¦ÊB was inhibited.When porcine neutrophils were stimulated with LPS, the anti-inflammatory effect of gallic acid was mainly mediated by inhibiting the activity of cellular phosphodiesterase 4 (PDE4) and reducing TNF-¦Á, but was not directly related to the expression of PDE4 Relationship.In a mouse model of colitis induced by dextran sulfate sodium,gallic acid can effectively inhibit the activation of signal transcription and transduction factor p-STAT3Y705 and its accumulation in the nucleus,prevent the degradation of I¦ÊB in the colonic mucosa and inhibit p65-NF .The -¦ÊB complex is translocated into the nucleus.Gallic acid can also prevent the occurrence of inflammatory tumors by inhibiting the activation of NF-¦ÊB and protein kinase B (Akt) signaling pathways and the activities of enzymes such as cyclooxygenase and ribonucleotide reduction.

Derivatives of gallic acid also have anti-inflammatory properties.Derivatives of chitosan and gallic acid can inhibit the activity of activator protein-1 (AP-1) through phosphorylation of mitogen-activated protein kinase (MAPK) pathway and exert anti-inflammatory effects; methyl gallate can inhibit neutrophils.The recruitment of inflammatory mediators,the secretion of inflammatory mediators,and the phosphorylation of key proteins in inflammatory pathways,etc.,indicate that gallic acid can exert anti-inflammatory effects through multiple inflammatory pathways.A large number of cytological studies have proved that gallic acid can inhibit the activation of NF-¦ÊB and the expression levels of various downstream inflammatory factors,but the exact molecular mechanism of its anti-inflammatory has not been fully elucidated.2.4 Anti-tumor effectGallic acid can exert anti-tumor properties by inhibiting tumor cell growth and inducing tumor cell apoptosis.In vitro experiments showed that gallic acid at a concentration of more than 10 ¦Ìmol/L could exert an anti-tumor effect in a dose-dependent manner within a certain range.

The anti-tumor mechanism of gallic acid is mainly through the following points: 

1. Cytotoxicity:Gallic acid has selective cytotoxicity to a variety of tumor cells, and has no effect on the growth of normal cells, which is mainly related to the increase in the content of transferrin receptors in tumor cells and the difference in metabolic capacity from normal cells. 

2. Consume GSH and induce intracellular production of reactive oxygen species.Gallic acid-induced apoptosis may be related to oxidative stress caused by reactive oxygen species and mitochondrial dysfunction,and induce oxidative damage to macromolecules such as proteins and lipids,resulting in tumor cell death.Gallic acid can also cause oxidative damage to DNA by depleting GSH,which is mainly related to the reduction of enzymatic activity and the expression of related enzymatic proteins. 

3. Induction of apoptosis, studies have shown that gallic acid can induce apoptosis in 3T3-L1 preadipocytes and HeLa cells by up-regulating BCL2-associated X protein (Bax) and down-regulating B-lymphoma-2 (Bcl-2) expression,and induces intracellular effector half Activation and cascade effects of caspases.Cysteine ??proteases are key enzymes that induce apoptosis.Once activated by signaling pathways,they can induce apoptosis by cleaving proteins, triggering nuclear lamina and cytoskeleton disintegration.In addition,gallic acid can also exert anti-cancer effects such as anti-angiogenesis and inhibition of cyclooxygenase activity.

3 Application of gallic acid in livestock and poultry production

Gallic acid can be used as a feed additive in the European Union.The European Food Safety Authority (EFSA) has comprehensively evaluated the safety and effectiveness of adding gallic acid to livestock and poultry diets,and given that the dosage of gallic acid in livestock and poultry diets is 25 Below mg/kg, "Catalogue of Feed Additives (2013)" stipulates that propyl gallate can be used as an antioxidant in the production of farmed animals,while gallic acid is not included in the list of feed additives,but domestic manufacturers are actively applying for gallic acid as a feed additive use.Gallic acid has strong application prospects in livestock and poultry production due to its good anti-oxidative, anti-inflammatory and antibacterial functions,and does not lead to drug resistance in animals.It has strong application prospects in livestock and poultry production.Preliminary studies have shown that the addition of an appropriate amount of gallic acid or related mixtures to the diet can regulate the growth and health of livestock and poultry.

3.1 Growth-promoting effect

Adding moderate amounts of gallic acid to broiler and piglet diets can promote animal growth and improve feed conversion. And other studies have shown that adding 5 g/kg of gallic acid to the diet can improve the feed conversion rate of broilers (1-35 days old),added 5 g/kg of gallic acid to the broiler diet,and the feed-to-weight ratio of broilers from 1 to 35 days of age was significantly reduced.Samuel et al. added lower doses (25-150 mg/kg) of gallic acid to broiler diets and found that 75 or 100 mg/kg of gallic acid could significantly improve the feed conversion ratio of broilers from 1 to 42 days of age.Salaheen et al. added 0.1 g/L gallic acid to the drinking water of broilers. After 42 days of conventional feeding,the body weight of broilers increased by 5.8%. Korea Qing et al. added 100, 300, and 500 mg/kg of gallocatechin gallate to the diets of weaned piglets, and the piglets' feed intake and weight gain were significantly increased.

3.2 Antioxidant effect

Adding gallic acid to the diet can improve the body's antioxidant capacity,remove excess reactive oxygen species produced in the body,and maintain the balance of the body's redox system,confirmed that adding 75-100 mg/kg of gallic acid to the diet can improve the plasma antioxidant properties of broilers, added a mixture of 0.05% and 0.10% gallic acid and linoleic acid (1:1, molar ratio) to the broiler diet,the body's activity of scavenging DPPH free radicals was enhanced,and the antioxidant activity of chicken was improved.The study by Jung et al. found that adding 0.05% and 0.10% mixture of gallic acid and linoleic acid (1:1, molar ratio) to the diet of laying hens improved the antioxidant capacity of eggs,improved the fatty acid composition of egg yolk,and reduced the level of egg yolk cholesterol.Korea Qing reported that gallate can reduce the concentration of malondialdehyde (MDA) in piglet blood and increase the activities of superoxide dismutase and catalase (CAT).Hanczakowska et al. divided 42 ternary hybrid fattening pigs into 3 groups according to their body weight. In the gallic acid test group, 50 mg/kg of gallic acid was added, and the feeding cycle was from 60 to 113 kg of pig body weight.Improving the antioxidant properties of pork can significantly reduce the content of thiobarbituric acid reactive substances in pork after 6 months of freezing. Zhao Guangyong added 5.3, 10.5, and 21.1 g/kg DM gallic acid to beef cattle diets,and found that plasma CAT activity increased linearly.In addition, polyphenols containing gallic acid and its derivatives are added to animal diets to improve the body's antioxidant function.Yang et al. showed that the addition of 7.5 or 15.0 mg/kg of grape proanthocyanidins (a catechin,epicatechin and oligomers of their gallates) to broiler diets significantly increased 21 and 42 Plasma superoxide dismutase (SOD) activity in day-old broilers and decreased MDA concentrations in 42-day-old broilers.

3.3 Improve gut health

Dietary gallic acid can improve animal gut morphology and modulate microbial diversity, thereby regulating the absorptive function and health of the animal gut. Ma?ek et al. added 5 g/kg gallic acid to the basal diet of broilers,which significantly increased the concentration of total short-chain fatty acids and acetic acid in the body,and improved the fermentation of caecal contents in broilers.Samuel et al.concluded that gallic acid improved growth and antioxidant activity in broilers,and also found that dietary supplementation of gallic acid at 50, 75, and 100 mg/kg could reduce jejunal villus crypt depth and increase villus height/crypt depth by reducing jejunal villus crypt depth.(VCR), improved jejunal epithelial morphology in broilers.Salaheen et al.found that adding 0.1 g/L gallic acid to drinking water could modulate the diversity of microbial flora in broilers,increase the number of Firmicutes in the caecum and reduce the number of Bacteroidetes,and increase Firmicutes/Pseudobacterium Bacillus phylum,thereby promoting the growth of broilers.In addition, dietary supplementation of polyphenols containing gallic acid and its derivatives (grape proanthocyanidins) also improved gut health in broilers.Viveros et al. added 60 g/kg of grape proanthocyanidins to broiler diets,which enriched the microbial biodiversity in the cecum of 21-day-old broilers and significantly improved the VCR of the jejunum of broilers.Yang et al. found that dietary supplementation of grape proanthocyanidins at 7.5 and 15.0 mg/kg could significantly reduce jejunal crypt depth and increase jejunal VCR in 21- and 42-day-old broilers.

3.4 Reducing Methane Emissions

Adding a certain amount of gallic acid to the diet can reduce the emission of ruminant methane and nitrous oxide in the feces of ruminants.Play an important role in ruminant production and environmental protection.Zhao Guangyong's study found that compared with the control group,the DM group with gallic acid addition ¡Ý 10.5 g/kg reduced methane production and the relative abundance of methanogens,and linearly decreased acetic acid/propionic acid; gallic acid addition ¡Ý 5.3 g/kg kg DM group changed.