A polypeptide-type natural antimicrobial agent produced by fermentation of Lactococcus lactis, classified as a safe biological preservative that meets consumer demand for “natural, chemical-free preservation.” It exhibits excellent heat stability and maintains activity under acidic conditions. It specifically inhibits spoilage- and pathogenic-related Gram-positive bacteria in foods without altering original flavor or nutritional components and without disrupting beneficial gut microbiota. It is easily broken down by human digestive enzymes with no residue risk, enhancing market competitiveness of finished products.