2) Acidifier should promote intestinal microecological balance and prevent intestinal pathogenic microbial diseases in animals.
A balanced and stable micro-ecological environment is important to prevent animal diseases. The suitable pH for the growth of several pathogenic bacteria is neutral alkaline, such as the appropriate pH of E. coli is 6.0-8.0, streptococcus is 6.0-7.5, staphylococcus is 6.8-7.5, clostridium is 6.0-7.5, and lactic acid Bacillus and the like are suitable for reproduction in an acidic environment. Therefore, by reducing the pH of the gastrointestinal tract, acidifiers can inhibit the reproduction of harmful microorganisms, reduce the consumption of nutrients and the production of bacterial toxins, and promote the proliferation of beneficial bacteria. In addition to lowering intestinal pH, organic acids have another mechanism of action to kill pathogens. After entering the animal's gastrointestinal tract, some of the organic acids dissociate to produce hydrogen ions, which lowers the pH value, while other parts do not dissociate but exist in molecular form. Only this part of the organic acids in molecular form can enter the bacteria through the cell membrane of the bacteria. In bacterial cells, the pH is neutral, so organic acid molecules will dissociate here to produce hydrogen cations and carboxylate anions. Hydrogen cations will reduce the pH value of bacterial cells. To maintain normal life, bacteria must maintain the pH value of the cells at about 7.0. Therefore, bacterial cells need to discharge hydrogen cations to the outside of the cells through the H + -ATP pump. This process consumes a lot of Energy (ATP), which inactivates bacteria. On the other hand, carboxylate anions can inhibit the synthesis of DNA and proteins in the nucleus of bacteria, making bacteria unable to reproduce the next generation (Stratford & Anslow, 1998; Russel & Diez-Gonzales, 1998; Roeetal., 1998). Therefore, the direct bactericidal effect of the acidifying agent depends on the dissociation degree of the acid. The lower the dissociation degree, the stronger the acid sterilization effect, and the higher the dissociation degree, the worse the direct bactericidal effect of the acid. In general, inorganic acids (such as phosphoric acid) have a high degree of dissociation, so their direct bactericidal effect is poor; organic acids have a low degree of dissociation, and their bactericidal effect is relatively strong. The bactericidal effect of different organic acids among organic acids is also different. Among them, citric acid and lactic acid have a lower sterilization effect because of higher dissociation than other organic acids. Formic acid, acetic acid, and propionic acid have better sterilization effects. Therefore, formic acid, acetic acid and propionic acid are ideal organic acids with bactericidal effect. In addition, the role of acidifiers also depends on the concentration of the acid and the number of molecules. The higher the concentration, the more the number of molecules, and the better the effect, so the bactericidal effect of macromolecular organic acids is relatively poor.
Inorganic acids can inhibit the growth of some bacteria by lowering the intestinal pH. However, because of the rapid dissociation of inorganic acids, it is difficult to reach the posterior intestinal tract, so the actual antibacterial effect of inorganic acids is not good. The large-molecule organic acid is difficult to enter the bacterial cell because of its large molecule, so the antibacterial effect of the large-molecule organic acid is not as good as that of the small-molecule organic acid.
In addition, research shows that composite organic acids composed of small-molecule organic acids have stronger antibacterial effects than single-molecule organic acids. Panyu (1997) tested the lowest bacteriostatic concentration of formic acid, acetic acid, propionic acid, fumaric acid, citric acid, and lactic acid against E. coli, and found that the lowest effective bacteriostatic concentration of formic acid, that is, the best bacteriostatic effect Followed by propionic acid, acetic acid and fumaric acid, lactic acid and citric acid had the worst antibacterial effect. They also found that the complex of formic acid and propionic acid was 2-4 times more bacteriostatic than formic acid or propionic acid.