Biodegradable polylactic acid polymer with nisin for use in antimicrobial food packaging

ABSTRACT:  Biodegradable polylactic acid (PLA) polymer was evaluated for its application as a material for antimicrobial food packaging. PLA films were incorporated with nisin to for control of foodborne pathogens. Antimicrobial activity of PLA/nisin films against Listeria monocytogenes , Escherichia coli O157:H7, and Salmonella Enteritidis were evaluated in culture media and liquid foods (orange juice and liquid egg white). Scanned electron micrograph and confocal laser microscopy revealed that nisin particles were evenly distributed in PLA polymer matrix on the surface and inside of the PLA/nisin films. PLA/nisin significantly inhibited growth of L . monocytogenes in culture medium and liquid egg white. The greatest inhibition occurred at 24 h when the cell counts of L. monocytogenes in the PLA/nisin samples were 4.5 log CFU/mL less than the controls. PLA/nisin reduced the cell population of E. coli O157:H7 in orange juice from 7.5 to 3.5 log at 72 h whereas the control remained at about 6 log CFU/mL. PLA/nisin treatment resulted in a 2 log reduction of S. Enteritidis in liquid egg white at 24 °C. After 21 d at 4 °C the S. Enteritidis population from PLA/nisin treated liquid egg white (3.5 log CFU/mL) was significantly less than the control (6.8 log CFU/mL). E. coli O157:H7 in orange juice was more sensitive to PLA/nisin treatments than in culture medium. The results of this research demonstrated the retention of nisin activity when incorporated into the PLA polymer and its antimicrobial effectiveness against foodborne pathogens. The combination of a biopolymer and natural bacteriocin has potential for use in antimicrobial food packaging.