Nisin is a natural antimicrobial substance used primarily as a food preservative. It helps to extend the shelf life of food products by inhibiting the growth of undesirable microorganisms.
Understanding Nisin’s Nature
Nisin is a bacteriocin, a peptide produced by bacteria. It originates from certain strains of Lactococcus lactis, a food-grade lactic acid bacterium. This polypeptide consists of 34 amino acid residues and contains unusual amino acids like lanthionine and methyllanthionine, forming distinctive ring structures. These unique structural features classify nisin as a lantibiotic.
The Process of Nisin Production
The preparation of nisin begins with a fermentation process using specific strains of Lactococcus lactis. These bacteria are cultured in a nutrient-rich medium, often containing natural substrates such as dextrose or milk. During their growth phase, Lactococcus lactis bacteria produce and secrete nisin into the fermentation broth.
Following fermentation, nisin must be separated and purified from the bacterial culture. This downstream processing extracts and concentrates the peptide. Initial methods include centrifugation to remove bacterial cells, followed by techniques like salt precipitation to separate nisin from other components in the broth.
Further purification often employs chromatographic methods, like cation exchange chromatography, which uses nisin’s positive charge at acidic pH. This allows for the selective binding and elution of nisin using varying salt concentrations, such as a five-step sodium chloride gradient. Final commercial preparations of nisin are available as concentrated powders, containing around 2.5% to 33% nisin, alongside other components like sodium chloride.
How Nisin Works as a Preservative
Nisin functions as an antimicrobial agent by targeting and disrupting the cell membranes of susceptible bacteria. As a positively charged peptide, it initially binds to the negatively charged plasma membranes of these microorganisms. This binding allows nisin to form pores in the cytoplasmic membrane, leading to the dissipation of the membrane potential and pH gradient within the bacterial cell.
The pore formation mechanism results in the leakage of essential cellular components, leading to bacterial inactivation and death. Nisin is particularly effective against Gram-positive bacteria, including common food spoilage organisms and pathogens like Listeria monocytogenes, Staphylococcus aureus, and Clostridium botulinum. It is also effective against bacterial spores, which are often resistant to other preservation methods.
Widespread Uses of Nisin
Nisin is applied as a natural food preservative across many food categories to extend shelf life and enhance safety. Its use is prominent in dairy products, including processed cheeses, milk, and yogurts, where it inhibits spoilage bacteria. It also finds extensive application in canned foods, contributing to their stability and preventing bacterial contamination during the canning process.
The preservative is also incorporated into meat products to control the growth of spoilage and pathogenic bacteria on surfaces. Nisin is used in beverages such as fruit juices, soft drinks, beer, and wine, helping to maintain their freshness. Beyond food, nisin has emerging applications in areas like human ulcer therapy, mastitis control in cattle, and in some cosmetic and health products.
Ensuring Nisin’s Safety
Nisin is recognized for its safety as a food additive due to its natural origin and degradation in the digestive system. In the United States, nisin has achieved Generally Recognized As Safe (GRAS) status, affirmed by the FDA under 21 CFR 172.385. This designation confirms its safety for use as an antimicrobial agent to inhibit the outgrowth of Clostridium botulinum spores in certain food products.
Similarly, in the European Union and other regions, nisin is approved as a food additive and is identified by the E number E234. Regulatory bodies like the European Food Safety Authority (EFSA) have evaluated nisin’s safety, establishing an acceptable daily intake. Its natural production by lactic acid bacteria and its specific activity against target microorganisms, without cross-resistance with medical antibiotics, contribute to its safety profile.