Organic acids are widespread in nature (animal, vegetable and microbial sources) and are produced by several fungi, yeasts and bacteria. Organic acids are categorized into the “weak” acid group, which does not completely dissolve in water, and they comprise one or more carboxylic acid groups covalently linked in groups such as amides, esters, and peptides.
Properties of organic acids
The acid and base properties of organic compounds are very similar to the acid and base properties of inorganic compounds. The properties of acids include a pH less than 7, an acidic taste, the formation of hydrogen ions when dissolved in water, and their corrosive effect on human tissues and their reaction with bases to form salt and water. Common properties of bases include a pH greater than 7, a “soapy” feel, a bitter taste, and being corrosive to human tissues and reacting with acids to form a salt and water. Pigs are about ten times more sensitive to sour tastes than to sweet tastes.
How many types of organic acids are there?
There are two types of organic acids. One has the carboxyl group (COOH group), for example acetic acid (CH3COOH) that is produced by oxidizing grain alcohol or by fermenting fructose in cider. The second type has a phenol group (C6H5OH). Salicylic acid (OHC6H4COOH) is an example of an organic acid with both carboxylic and phenolic groups.
Why are organic acids important?
Organic acids play a role in the regulation of fundamental cellular processes such as pH modification, signaling messengers, and modulation of transport across biological membranes, and they extensively modify the cellular, subcellular, or extracellular compartments in which they reside due to their chemical properties. Therefore, organic acids can be involved in various biochemical and physiological processes in vivo. In addition, organic acids are involved in the chemical modification of proteins, with a high impact on the in vivo protein activity. The various roles of these compounds have yet to be explored.
Production and extraction of organic acids
Chemical synthesis or fermentation are among the most commonly used methods to produce organic acids. In recent years, new techniques for the rapid and efficient extraction of organic compounds from various plant materials have been developed. Citric, lactic, gluconic, and itaconic acids are industrially produced by microbial processes, which is a promising approach to obtain building block chemicals based on renewable carbon sources. In addition, large amounts of acetic acid are produced by bioprocesses and chemical synthesis. Microwave-assisted extraction is another technique for isolating various compounds from plants or plant materials for both analytical and industrial purposes.
Positive effect of organic acids
The positive effects of organic acids include:
reducing the rate of emptying of the stomach;
stimulation of enzyme secretion and activity in the gut;
supply of nutrients to the intestinal tissue;
improving the integrity and function of the mucosa;
Improving the activity of pepsin and microbial phytase;
inducing pancreatic secretion;
increase in protein digestion;
improving mineral utilization;
reducing competition between the microflora and the host; and
Improving pig health and productivity.
Organic acids can directly lower the pH of the intestinal environment by releasing hydrogen ions, thereby preventing or inhibiting the proliferation of acid-sensitive bacteria. The antimicrobial effect of organic acids is greater in acidic conditions and less in neutral pH. It is important to know that each organic acid has a spectrum of microbial activity involved in a specific pH range, membrane structure and physiology in the cell of the microbiota species. In addition, organic acids are promising alternatives to antibiotics to promote nutrient digestibility by lowering pH in the upper digestive tract.
The most commonly used organic acids in pig nutrition
The most commonly used organic acids in pig nutrition include citric, lactic and formic acid.
Citric acid is an odorless, colorless compound with an acidic, sour-tasting character. It is mainly used as a flavoring agent and preservative in soft drinks and confectionery, as a disinfectant and to stabilize or preserve medicines. Citric acid releases minerals bound to the phytate molecules, which in turn increases the utilization of calcium, phosphorus and zinc. Citric acid supplementation improves digestibility of dry matter, nitrogen and energy in finishing pigs and lactating sows and digestibility of crude protein, dry matter, fat and energy in growing pigs. In addition, the addition of citric acid to the feed of breeding and fattening pigs decreases Escherichia coli counts and increases lactobacilli what matters is what improves gut health. In addition, feed supplemented with citric acid reduces the emission of vinegar gas and the concentration of ammonia in fattening pigs.
Lactic acid is an odorless, colorless, metal and tissue corrosive liquid produced during fermentation. Feeding weaned pigs a lactic acid-supplemented diet improves average daily weight gain, average daily feed intake, feed efficiency and performance. In weaned pigs, supplementing the feed with lactic acid improves dry matter digestibility, increases the concentration of bacilli and lactobacilli, and reduces salmonella and E. coli counts.
Formic acid is a colorless liquid with a pungent odor. It is corrosive to metals and fabrics. Formic acid is the simplest carboxylic acid and is found in various sources such as bee venom and ant stings. It is also used as a preservative and antibacterial agent in cattle feed. Formic acid reduces bacterial nitrogen in pig intestines and improves apparent ileal digestibility of crude protein, essential amino acids, lipids, calcium and phosphorus. In addition, formic acid supplementation improves dry matter digestibility in weaned pigs and improves gut health.
Organic acids reduce gastric pH, prevent the growth of pathogens, act as a source of energy, increase apparent overall digestibility, improve gut health, and increase growth performance and productivity. However, the effect of organic acids is not always the same in practice due to the large number of products available and the different recommended effective dosages for the different combinations. Species composition, dosage, formula, feeding schedule, environment, nutritional composition of the feed, and the age and health of the animals affect the effectiveness of organic acids. As such, research is still needed to determine an effective dosage and combination of organic acids to achieve the best possible results.