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Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/11/2009 Publication Date: 3/4/2010 Citation: Jin, Z.T. 2010. Inactivation of Listeria monocytogenes in Skim Milk and Liquid Egg White by Antimicrobial Bottle Coating with Polylactic Acid and Nisin. Journal of Food Science. 75(2):M83-M88. Interpretive Summary: Recent outbreak of Listeria monocytogenes infections associated with pasteurized milk in Massachusetts raised more public concerns over the safety of dairy foods. In 2007, five cases of listeriosis were identified, and three deaths occurred in residents of central Massachusetts. This outbreak illustrated the potential for contamination of fluid milk products after pasteurization. Cells of L. monocytogenes have been isolated from commercially processed liquid whole egg in the U.S. and Northern Ireland. Although no outbreaks of listeriosis have been attributed to eggs, the potential exists for survival and growth of L. monocytogenes in egg products. Therefore, there is a need to develop an intervention technology to reduce the outbreaks due to Listeria contamination. This project was to extend our previous studies to develop an antimicrobial packaging system for liquid foods to inactivate food borne pathogens which may survive thermal pasteurization or come from post-pasteurization contamination. In this study, L. monocytogenes, liquid egg and milk were used as a model for evaluating the efficacy of polylactic acid (PLA)/nisin bottle coating in inactivating the pathogen in liquid foods. The PLA coating with 250 mg nisin completely inactivated the cells of L. monocytogenes in milk after 3 days and throughout the 42 day storage period. The treatment of PLA coating with 250 mg nisin rapidly reduced the cell numbers of Listeria in liquid egg white to undetectable level after 1 day, and then remained undetectable throughout the 48 day storage period at 10C and the 70 day storage period at 4C. This study demonstrated the commercial potential of applying the antimicrobial bottle coating method to milk, liquid eggs, and possibly other fluid products. Technical Abstract: This study was to develop an antimicrobial bottle coating method to reduce the risk of outbreaks of human listeriosis caused by contaminated liquid foods. Liquid egg white and skim milk were inoculated with Listeria monocytogenes Scott A and stored in glass jars that were coated with a mixture of polylactic acid (PLA) polymer and nisin. The efficacy of PLA/nisin coating in inactivating L. monocytogenes was investigated at 10C and 4C. The pathogen grew well in skim milk without PLA/nisin coating treatments, reaching 8 log CFU/ml after 10 days and then remained constant up to 42 days at 10C. The growth of Listeria at 4 C was slower than that at 10C, taking 21 days to obtain 8 log CFU/ml. At both storage temperatures, the PLA coating with 250 mg nisin completely inactivated the cells of L. monocytogenes after 3 days and throughout the 42 day storage period. In liquid egg white, Listeria cells in control and PLA coating without nisin samples declined 1 log CFU/ml during the first 6 days at 10C and during 28 days at 4C, and then increased to 8 or 5.5 log CFU/ml. The treatment of PLA coating with 250 mg nisin rapidly reduced the cell numbers of Listeria in liquid egg white to undetectable level after 1 day, then remained undetectable throughout the 48 day storage period at 10C and the 70 day storage period at 4C. These data suggested that the PLA/nisin coating treatments effectively inactivated the cells of L. monocytogenes in liquid egg white and skim milk samples at both 10C and 4C. This study demonstrated the commercial potential of applying the antimicrobial bottle coating method to milk, liquid eggs, and possibly other fluid products. |
