Antibacterial and anti‐biofilm of epsilon‐poly‐lysine hydrochloride on Listeria monocytogenes and its application on refrigerated beef

The aim of this study was to investigate the antibacterial characteristics and anti-biofilm ability of epsilon-poly-lysine hydrochloride (ε-PLH) against Listeria monocytogenes. Minimum inhibitory concentration of ε-PLH against L. monocytogenes was 16 μg/ml. Scanning electron microscopy showed that ε-PLH damaged the morphology of tested bacterial cells. The decrease in cell metabolic activity and two intracellular enzymes of β-galactosidase and ATPase, and the increase of electrical conductivity, protein, and absorbance at 260 nm in the treated suspension indicated that cell membranes were broken by ε-PLH, which caused leakage of ions and intracellular materials of L. monocytogenes. Moreover, ε-PLH at maximum sublethal concentration significantly repressed the biofilm formation, exopolysaccharide production, and cell adhesion, which was consistent with the reduction of swimming and AI-2 activity. Finally, ε-PLH was applied to preserve refrigerated beef steak and showed the remarkable anti-listerial activity and improvement of sensory quality. Practical applications Listeria monocytogenes is a foodborne pathogen that can cause invasive severe human cases of listeriosis. Although initial contamination levels in foods are usually low, the ability of these bacteria to survive and multiply at low temperatures allows it to reach levels high enough to cause disease. Furthermore, biofilm cells of L. monocytogenes are more resistant to cleaning and disinfectants than planktonic cells, leading to their survival for lengthy periods in food processing plant environment. Moreover, epsilon-poly-lysine hydrochloride (ε-PLH) as homopolymer of epsilon-poly-lysine (ε-PL) becomes currently the main product due to lower price and more stable during storage compared with ε-PL. At present, ε-PL with antimicrobial properties is well documented, however, there is little research on the effect of ε-PLH on the planktonic and biofilm cells of L. monocytogenes. This work may provide a reference for the development of new efficient and economic preservatives in controlling L. monocytogenes in the meat processing industry.