Nisin under acidic conditions

Nisin is a biological preservative commonly used in the food industry. It has good stability and antibacterial activity under acidic conditions. The following is a specific introduction to the relevant research:

I. Stability under Acidic Conditions

Influence of pH value: Nisin has good stability in an acidic environment. Studies have shown that when the pH value is between 2 and 4, it can maintain high activity, and its structure is relatively stable. This is because under acidic conditions, some key groups in the nisin molecule, such as amino groups, will be protonated, making the molecular structure more compact and less likely to be degraded by external factors such as proteases. For example, in a citric acid-sodium citrate buffer solution with a pH of 3, after Nisin is placed at room temperature for several weeks, its activity loss is small.

Influence of temperature: Under acidic conditions, temperature has a certain influence on the stability of nisin. At lower temperatures, it can maintain good stability. Even under high-temperature and short-term treatment conditions, such as in an acidic solution with a pH of 3, after treatment at 121°C for 15 to 30 minutes, nisin can still retain a considerable part of its activity. However, as the temperature increases and the treatment time is prolonged, its activity will gradually decrease. This may be due to changes in its molecular structure caused by high temperature, such as the extension of the peptide chain and the breaking of disulfide bonds. But its stability under acidic conditions is still better than that under neutral and alkaline conditions.

II. Antibacterial Activity under Acidic Conditions

Inhibitory effects on different microorganisms: Under acidic conditions, nisin has a strong inhibitory effect on a variety of Gram-positive bacteria. For example, for Staphylococcus aureus, Listeria, Bacillus, etc., it can more effectively exert its antibacterial effect in an acidic environment. Taking Staphylococcus aureus as an example, in an acidic medium with a pH of 4 to 5, adding a certain concentration of nisin can significantly inhibit its growth and reduce the number of bacteria. This is because the acidic environment helps it better adsorb on the bacterial cell membrane, increase the permeability of the cell membrane, and thus more effectively inhibit the growth and reproduction of bacteria. For Gram-negative bacteria, although the inhibitory effect of nisin used alone is relatively weak, under acidic conditions, the permeability of their cell membranes will increase, making it easier for nisin to enter the cells, thereby enhancing the inhibitory effect on Gram-negative bacteria.

Synergistic effects with other factors: Under acidic conditions, the antibacterial activity of nisin can also produce synergistic effects with other factors. For example, when used in combination with some acidic preservatives such as benzoic acid and sorbic acid, they can produce a synergistic antibacterial effect. This is because acidic preservatives can reduce the environmental pH value, further enhancing the stability and antibacterial activity of Nisin. At the same time, different preservatives act on different targets of bacteria, thus more comprehensively inhibiting the growth of bacteria. In addition, some chelating agents such as EDTA can also act synergistically with it under acidic conditions. EDTA can remove divalent metal ions outside the bacterial cell membrane, making the cell membrane structure loose and facilitating the better action of nisin on the cell membrane, thereby improving the antibacterial effect.

Nisin has good stability and strong antibacterial activity under acidic conditions, which gives it broad application prospects in the preservation and anti-corrosion of acidic foods. At the same time, through synergistic effects with other substances, its antibacterial effect can be further improved, providing better protection for the safety and quality of foods.