The stability and application of Nisin

Nisin is a naturally occurring bioactive antimicrobial peptide produced by Streptococcus lactis. It exhibits excellent stability and broad application value. Below is an introduction to its stability studies and applications in food processing:

Studies on the Stability of Nisin

Influence of pH on stability: Nisin is relatively stable under acidic conditions. When pH < 6.0, only slight activity loss occurs after heat treatment. However, its stability decreases significantly as pH increases. When the solution pH exceeds 6.0, nisin undergoes intramolecular nucleophilic addition reactions, leading to structural changes, which reduce its water solubility, thermal stability, and antibacterial activity.

Influence of temperature on stability: Nisin has good heat resistance and retains activity even under autoclaving conditions (121°C), making it suitable for preservative processes in heat-processed foods. Nevertheless, its activity is significantly affected in high-temperature and alkaline environments. Relatively, refrigeration temperatures are more conducive to maintaining its activity.

Influence of other factors on stability: Certain components in food can protect Nisin, enhancing its stability. For example, in food systems containing proteins, fats, and other components, the stability of nisin improves. Additionally, nisin is particularly sensitive to proteolytic enzymes (such as trypsin), which can hydrolyze it. Thus, its stability decreases in environments rich in such enzymes.

Applications of nisin in Food Processing

Dairy products: Dairy products are rich in nutrients and susceptible to microbial contamination. Nisin can be used in various dairy products such as pasteurized milk, skim milk, and sugar-free condensed milk. It compensates for the limitations of low-temperature sterilization, inhibits the germination of heat-resistant Gram-positive bacterial spores, reduces the intensity of high-temperature treatment, and extends the product shelf life. It can also prevent post-acidification in yogurt and control the increase in acidity during storage and transportation.

Meat products: Nisin can effectively replace colorants such as nitrites, reducing the usage of colorants in ham and lowering the risk of nitrosamine formation. Meanwhile, it effectively controls microbial growth in meat products, particularly inhibiting the activity of Clostridium botulinum. It also reduces the intensity of heat treatment, preserving the texture and appearance of meat products.

Canned foods: Conventional can sterilization struggles to completely eliminate heat-resistant spore-forming bacteria, but adding Nisin can effectively address this issue. For high-acid foods (pH < 4.5), the stability, solubility, and activity of Nisin are enhanced, resulting in better preservative effects. Adding nisin to low-acid and non-acidic canned foods reduces the intensity of heat treatment, preserves the nutritional value and flavor of the food, and extends shelf life.

Beer: In beer brewing, nisin can be added to cold wort to prevent contamination of yeast by Gram-positive bacteria and into fermentation mash to control the growth of miscellaneous bacteria. It can also replace traditional acid washing to eliminate lactic acid bacteria contaminating yeast. For both draft beer and pasteurized beer, Nisin extends shelf life or reduces sterilization temperature and time, improving beer taste and saving energy.

Fruit juice beverages: Fruit juices and fruit juice-based beverages are prone to spoilage due to contamination by microorganisms such as Bacillus acidoterrestris. Nisin has strong inhibitory effects on most Gram-positive bacteria, especially spore-forming bacteria. Its application in fruit juice beverages effectively inhibits the growth of related microorganisms and prevents beverage spoilage.