Submitted to: Food Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/8/2005
Publication Date: 10/1/2005
Citation: Ukuku, D.O., Cooke, P.H. 2005. Effect of sanitizing treatments on cantaloupe surface structure, removal of bacteria and re-contamination with salmonella. Food Microbiology. 23:289-293. Interpretive Summary: The surface of cantaloupe rind is rough which may favor microbial attachment, and hinder any detachment protocol. Therefore any bacteria capable of causing human illness on cantaloupe surfaces can be transferred to fresh-cut pieces during cutting. In this study, we examined cantaloupe surfaces inoculated with Escherichia coli for possible areas of bacterial attachment and investigated the effect of chlorine, hydrogen peroxide and hot water treatments on the surface structures of whole cantaloupes using scanning electron microscopy (SEM). Also, we investigated whether prior decontamination of melons by sanitizer treatment affects vulnerability to recontamination by Salmonella. The SEM showed the majority of bacteria on cantaloupe surfaces were mostly attached at the netting more than the cuticle. Also, the SEM showed that hot water treatments slightly altered the surface structure of the cantaloupe netting, and reduced the microbial populations at this site better than treatment with chlorine or H2O2. The populations of Salmonella recovered from hot water treated cantaloupe surfaces exposed to Salmonella were higher than chlorine or hydrogen peroxide treated cantaloupes. The results of this study suggest that sanitized cantaloupe surface, containing smaller microbial populations, is susceptible to recontamination if exposed to a human bacterial pathogen. This finding will help the produce industry or fresh-cut processors in deciding how to handle sanitized cantaloupes to prevent re-contamination that could lead to foodborne illness episodes.
Technical Abstract: The surface of cantaloupe is comprised of a meshwork of tissue commonly referred to as the 'net' which gives the surface an inherent roughness that may favor microbial attachment and hinder detachment. Research was undertaken to examine surfaces of cantaloupe for possible areas of microbial attachment, to determine the effects of sanitizer and hot water treatments on cantaloupe surfaces and attached microbial populations, and to determine whether prior decontamination of melons by sanitizer treatment affects vulnerability to recontamination by Salmonella. Cantaloupes were submerged in 108 CFU/ml E. coli ATCC 25922 for 10 min, held at 5°C for 24 h, and then sanitized with 1000 ppm chlorine or 5% hydrogen peroxide solution for 2 min, or hot water (96°C) for 2 min. Cantaloupe surfaces were examined using scanning electron microscopy (SEM), both before and after inoculation and treatments with sanitizers or hot water. Observation by SEM of cantaloupe rind from inoculated melons showed the presence of attached bacteria on the cuticular surface with a higher microbial population within the netting. Hot water and chlorine treatments reduced the microbial populations at the cuticular surface and the microstructure of the netting as revealed by SEM. Similarly, plate counts revealed a 4.9 log reduction of total microbial populations on cantaloupe surfaces treated with hot water and approximately 2.6 log for melons treated with H2O2. Treatment with H2O2 was not as effective as hot water or chlorine, and the populations of native microflora and inoculated E. coli 29522 were not significantly (p>0.05) reduced. Uninoculated cantaloupes were sanitized and then inoculated with Salmonella. Higher populations of Salmonella were recovered from sanitized cantaloupes than from the untreated controls; recovery was greater from hot water treated melons than from cantaloupes treated with chlorine or hydrogen peroxide. Salmonella populations on sanitized cantaloupes appear to be inversely related to the population of surviving native microflora. The results of this study clearly show that bacteria preferably attach at the microstructure of the net. Sanitized cantaloupes are susceptible to recontamination if exposed to a human bacterial pathogen during subsequent handling.