Submitted to: Journal of Food Safety
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/23/2004
Publication Date: 11/1/2004
Citation: Ukuku, D.O., Fett, W.F., Sapers, G.M. 2004. Inhibition of listeria monocytogenes by native microflora of whole cantaloupe. Journal of Food Safety. 24:129-146. Interpretive Summary: There are many reports of disease due to consumption of fresh-cut cantaloupes that were contaminated with food borne pathogens. This study was designed to investigate whether the native microflora of whole cantaloupe surfaces are inhibitory to Listeria monocytogenes. Whole cantaloupe surface was treated with water, ethanol (70%) or chlorine (200 ppm) to reduce the native microflora on the melon surfaces. Both treated and untreated melons were inoculated with L. monocytogenes. We found that the decline in L. monocytogenes populations was less rapid in the ethanol or chlorine treated whole melon and fresh-cut pieces prepared from these melons. Higher populations of L. monocytogenes were attained in sterile tissue homogenates than in non-sterile homogenates. The results of this study clearly showed that certain classes of native microflora of whole cantaloupe surfaces can inhibit growth and survival of L. monocytogenes on cantaloupe rind and fresh-cut pieces. These findings will assist produce industry and regulatory industry in adopting prophylactic measures to ensure microbiological safety of produce.
Technical Abstract: Cantaloupe melon has never been associated with outbreaks of listeriosis due to contamination with Listeria monocytogenes suggesting that the naturally occurring microflora of cantaloupe surfaces may be antagonistic to pathogen attachment, growth or survival. To test this hypothesis whole melons were treated with water, ethanol (70%) or chlorine (200 ppm) to reduce the native microflora on the melon surfaces. Treated or untreated melons were immersed in a six strain cocktail of L. monocytogenes (108 CFU/ml) for 10 min and then allowed to dry for 1 h inside a biosafety cabinet followed by storage at 5, 10 and 20oC for 15 days. Fresh-cut pieces prepared from the treated or untreated melons and directly inoculated with L. monocytogenes (3.48 log CFU/g) were stored under the same conditions listed above. Populations of L. monocytogenes and five classes of native microflora were investigated. Growth of L. monocytogenes in sterile or non-sterile rind and fresh-cut homogenates was also studied. The population of L. monocytogenes recovered from inoculated (103 to 108 CFU/ml) whole melons given no disinfection treatment or washed with water was significantly less (p<0.05) than that recovered from melons treated with chlorine or EtOH. In general, populations of L. monocytogenes declined on the surface of treated and untreated whole melons and on fresh-cut pieces over the 15 days storage period at the temperatures tested. However, the decline in pathogen populations was less rapid in the presence of reduced populations of native microflora. Higher populations of L. monocytogenes were attained in sterile tissue homogenates than in non-sterile homogenates. Addition of yeast and mold to sterile rind homogenates was highly inhibitory to growth and survival of the pathogen. The results of this study indicate that native microflora of whole cantaloupe inhibited attachment to rind surfaces as well as survival and growth of L. monocytogenes on cantaloupe surfaces and homogenized fresh-cut pieces. Thus, L. monocytogenes recontamination of melons having a reduced level of native microflora following application of a disinfection treatment may be a food safety concern.