Nisin is a polycyclic peptide produced by Lactococcus lactis. It primarily consists of 34 amino acid residues, which are linked together by peptide bonds to form a polypeptide chain. Additionally, it contains some unique amino acids, such as thioether and methyl thioether groups, which may contribute to its important functional characteristics.

The molecular structure of nisin has cationic and hydrophobic properties, allowing it to effectively bind to microbial cell membranes and exert its antibacterial effects. Its molecular weight is approximately 3500 Da (or 3354.07 g/mol, with slight variations depending on the source), and its molecular formula is typically C₁₄₃H₂₂₈O₃₇N₄₂S₇. The structure includes five rare amino acids: ABA, DHA, DHB, ALA-S-ALA, and ALA-S-ABA, which form five internal rings through thioether bonds. The active molecules often exist as dimers or tetramers.

There are several variants of nisin, with Nisin A and Nisin Z being the two most extensively studied. The difference between these two variants lies in the type of amino acid at position 27: Nisin A has histidine (His), while Nisin Z has asparagine (Asn). This structural difference gives Nisin Z a higher solubility and enhanced antibacterial capacity.

In nisin products, in addition to the main nisin component, there may be some auxiliary ingredients, such as sodium chloride, which help maintain the product's stability and solubility and may influence its antibacterial efficacy.

The purity and activity of nisin are important indicators of its quality. High-purity and high-activity nisin demonstrate better antibacterial effects and a wider range of applications. Therefore, it is essential to strictly control the purity and activity of nisin during its production and application.

Nisin is a polycyclic peptide composed of 34 amino acid residues, with a unique molecular structure and various variants. The analysis of its composition is crucial for understanding its properties, functions, and applications.