Nisin

Nisin is a natural antimicrobial peptide, a bacteriocin made by strains of Lactococcus lactis during fermentation. It kills Gram-positive bacteria by punching pores in their cell membranes, which makes it a valuable biopreservative, coded E234, in processed cheese, meats, fish products, and canned fruits and vegetables, where it suppresses spoilage organisms and dangerous pathogens such as Listeria and Clostridium. Being a protein, it breaks down into harmless amino acids during digestion and has a long record of safe use. Regulations cap its level by food category, and its performance in any product hinges on pH, the food matrix, and which organisms are being targeted.