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Bacteriostatic Function of Acidifier and Bacteriostatic Comparison of Common Acid Raw Materials

2019/02/26 18:06
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ABSTRACT: At present, many countries in the world are seeking antibiotic substitutes that can promote animal growth. Acidifiers are considered to be the most commonly used and effective alternatives to antibiotics. Many studies have shown that adding Acidifiers to feed can improve animal production performance, feed utilization rate, protect animal gastrointestinal mucosa health, promote the growth of beneficial bacteria in gastrointestinal tract, inhibit the reproduction of harmful microorganisms, and enhance animal immune function. In this paper, the bacteriostasis function of acidifier and the comparison of bacteriostasis of common acid raw materials are reviewed.

Key words: acidifier; acid raw materials; bacteriostasis

Adding acidifier to feed can reduce the pH value of animal gastrointestinal tract, change the living environment of intestinal microorganisms, inhibit the growth and reproduction of harmful bacteria, even directly inhibit and kill harmful bacteria, and promote the growth of probiotics. Because the most suitable growth pH of pathogenic bacteria such as E. coli and Staphylococc*in the intestine of pigs is 6.0-7.5, and less than 4 can inhibit their growth, which is beneficial to the growth and reproduction of probiotics such as intestinal lactobacillus.

Adding different Acidifiers can promote the growth of piglets and reduce the incidence of diarrhea to different degrees; among them, 1.5% citric acid has obvious effect on reducing the number of coliform bacteria and the incidence of diarrhea; phosphoric acid has less effect than citric acid and compound acid.* Most scholars believe that dietary acidification can effectively control the number of harmful bacteria (E. coli, Salmonella, Staphylococcus, Clostridium) in the digestive tract of piglets.* The reason for reducing diarrhea rate of piglets is that Acidifier in diet reduces intestinal pH and destroys the suitable living environment of harmful microorganisms, but at the same time creates a suitable living and reproductive environment for beneficial bacteria such as lactic acid bacteria. Lactic acid and hydrogen dioxide, the metabolites of lactic acid bacteria, also inhibit and kill E*coli. Therefore, Acidifiers will help optimize the structure of intestinal microflora, reduce pathogenic bacteria infection, and cultivate a healthy intestine for animals.

1. The bacteriostatic and bactericidal effects of Acidifiers

Yang Fulin's study showed that compared with the control group, dietary supplementation of 1.7% and 3.3% citric acid reduced the number of E. coli in cecum and colon of weaned piglets by 91%, 8 l% and 95%, 87%, and the number of Lactobacillus increased by 95%, 86% and 97%, 92%, respectively. The average diarrhea rate of weaned piglets decreased by 60% and 64%, respectively. The results showed that Acidifiers not only inhibited pathogenic bacteria, but also protected beneficial intestinal flora. Lin Yingcai et al. considered that dietary supplementation of acidifier 1500g/t complex acid, mainly phosphoric acid, combined with citric acid, lactic acid and fumaric acid, increased the number of Lactobacillus, Escherichia coli and total bacteria in the small intestine of piglets, increased the proportion of Lactobacillus and decreased the proportion of Escherichia coli in the total bacteria, indicating that the rational ratio of complex acid not only directly affected the intestinal tract of piglets. The growth of bacteria mainly affects the balance of intestinal microflora.

1.1 bactericidal mechanism of organic acids

One of the antimicrobial ways of organic acids is to reduce the digestive tract pH by ionizing hydrogen ions, thus destroying the suitable living environment of harmful bacteria. Another way is to use undissociated organic acid molecules to penetrate the cell wall of Gram-negative bacteria and enter the cells. Then these organic acid molecules dissociate hydrogen ions and acid radicals from the relatively alkaline environment pH=7.4-7.5 in the bacteria. Hydrogen ions will reduce the intracellular pH. In order to restore their own pH balance and release protons, the cells will consume their own energy, resulting in a large amount of energy. In addition, the accumulation of acid ions can directly interfere with and block the synthesis of DNA in the nucleus. This dual mechanism of organic acids effectively inhibits the reproduction of bacteria.

1.2 Acids with different dissociation degrees have different physiological effects.

The main acids used as Acidifiers are citric acid, fumaric acid, lactic acid, phosphoric acid, formic acid, propionic acid, butyric acid and their salts. The results showed that the acidification ability of acidified rations was formic acid > phosphoric acid > tartaric acid > malic acid = citric acid > lactic acid > acetic acid. The effect of adding acid in feed is that acid can reduce the pH of diet on the one hand, and also benefit from the anti-bacterial effect of acid on the other. The effects of acids with different degrees of dissociation are different. Each acid has its own specific pK value. Its negative value is the pH value of 50% acid dissociation. The larger the pK value, the more difficult the acid dissociation is. For example, the pK value of formic acid is 3.77, while the pK value of propionic acid is 4.88. They show strong bactericidal and bacteriostatic effects in application. Phosphoric acid has three pK values, its minimum pK value is 1.96, so its dissociation degree is relatively large compared with organic acid, and the effect of reducing digestive tract pH in the combination of complex Acidifiers is very significant. Based on the theory of different dissociation degree of acidifier and synergistic bacteriostasis, some acids with high dissociation degree can be selected to reduce pH. Rational ratio of organic acids can make full use of the complementary and synergistic effects of different acids, which can not only reduce the digestive tract pH, improve the digestive tract physiological environment, but also play an effective bacteriostatic and bactericidal role, improve the digestive tract ecological environment. Its effect is superior to that of single acid, which has been confirmed by a large number of studies.

1.3 Volatile Organic Acids

It was found that there were obvious differences in the antimicrobial effects between volatile organic acids and non-volatile organic acids and inorganic acids. Volatile organic acids (formic acid, propionic acid and butyric acid) had better bactericidal effect. They diffused directly into cells and inhibited the metabolism of some macromolecules, such as DNA, RNA, protein or lipids, by reducing intracellular pH. The integrity of bacterial cell membrane can achieve the purpose of sterilization. Although formic acid and other bactericidal effects are obvious, but a large number of studies have also shown that formic acid or