Extruded Antimicrobial Film Targeting Gram-positive Pathogens

Introduction: Antimicrobial food packaging can help reduce spoilage, maintain food quality, extend shelf life and reduce or eliminate foodborne pathogens in ready-to-eat deli meat. Nisin is a polypeptide with natural antimicrobial activity against Gram-positive pathogens, including Listeria monocytogenes. As a food additive, it is generally recognized as safe (GRAS) in the United States.

Purpose: The goal of the study is to make a nisin-containing film that demonstrates antimicrobial activity.

Methods: Carver heat pressed studies using low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) were performed at different temperatures (130 °C, 140 °C, 150 °C and 160 °C) and pressed five times each to incorporate 5,000 IU/g of nisin A, nisin Z, or nisin (Sigma). The heat pressed films were tested for inhibition against L. monocytogenes using the plate overlay assay and inhibition zones were measured in millimeters (mm) from the edge of the film. Also, LLDPE were cast extruded at 130 °C and 170 °C and with 5,000 IU/g of nisin Z or sigma nisin and then heat pressed into a film. This film was tested for antimicrobial activity against L. monocytogenes using a plate overlay method. 

Results: All temperatures tested for the carver press study showed inhibition against Gram-positive bacteria with nisin Z demonstrating the largest inhibition zones. Inhibition for all nisin subtypes measured from 1 mm to 16 mm against all temperatures tested in the carver press. For extrusion studies, inhibition measured from 3.6 mm to 7.1 mm in LLDPE against L. monocytogenes.

Significance: This research is essential to the development of an antimicrobial vacuum skin package (VSP) for ready-to-eat (RTE) meat, which inhibits Gram-positive pathogens.