Submitted to: International Journal of Food Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/22/2005
Publication Date: 10/1/2005
Citation: Ukuku, D.O., Bari, M.L., Kawamoto, S., Isshiki, K. 2005. Use of hydrogen peroxide in combination with nisin, sodium lactate and citric acid in reducing transfer of bacterial pathogens from whole melon surfaces to fresh-cut pieces. International Journal of Food Microbiology. 104:225-233. Interpretive Summary: Food borne outbreaks due to consumption of fresh-cut melons contaminated with bacterial human pathogens have been a concern for the food industry and regulatory agencies. The inability of chlorine to completely inactivate human bacterial pathogens on whole melon surfaces and to eliminate transfer of bacteria from the melon rind to fresh-cut pieces suggests the need for other antimicrobial washing treatments. In order to improve the microbial safety of fresh-cut melons, whole cantaloupe and honeydew melons artificially contaminated with E. coli 0157:H7 and Listeria monocytogenes were washed at day 0 and 7 of refrigerated storage with hydrogen peroxide (2.5%) or hydrogen peroxide (1%) in combination with nisin, sodium lactate and citric acid. We observed that the combination treatment effectively reduced Listeria and E. coli populations on cantaloupe and honeydew melons by 99.999% and significantly reduced the transfer to below detection limit. The results of this study indicate that treatments of whole melon with hydrogen peroxide in combination with nisin, sodium lactate and citric acid would reduce transfer of spoilage microflora and pathogens from melon rind to the flesh during cutting thereby, improving the microbial safety of fresh-cut melons. This finding will be used by the produce industry in improving the safety of the food supply, thereby reducing the foodborne illness episodes.
Technical Abstract: Hydrogen peroxide (2.5%) alone or hydrogen peroxide (1%) in combination with nisin (25ug/ml), sodium lactate (1%), and citric acid (0.5%) as potential sanitizers for reducing Escherichia coli O157:H7 or L. monocytogenes populations on whole cantaloupe and honeydew melons were investigated. Whole cantaloupes inoculated with E. coli O157:H7 and L. monocytogenes at 5.27 and 4.07 log10 cfu/cm2, respectively, and whole honeydew melons inoculated with E. coli O157:H7 and L. monocytogenes at 3.45 and 3.05 log10 cfu/cm2, respectively, were stored at 5°C for up to 7 days. Antimicrobial washing treatments were applied to inoculated whole melons at days 0 and 7 of storage and surviving bacterial populations were determined. The effect of the washing treatments on transfer of Escherichia coli O157:H7 and L. monocytogenes to fresh-cut pieces prepared immediately after treatment was also determined. Treatment with Hydrogen peroxide (2.5%) alone significantly (p<0.05) reduced the populations of the pathogens at day 0. The combination of hydrogen peroxide with nisin, lactate and citric acid (HPNLC) resulted in reductions of approximately 4 log10 CFU/cm2 at day 0 for both types of whole melon. At day 7 post inoculation and treatment with HPNLC, populations of E. coli O157:H7 on cantaloupe and honeydew melons were reduced by approximately 2 and 3.5 log10 CFU/cm2, respectively, and were significantly (p<0.05) more effective than 2.5% hydrogen peroxide. While fresh-cut pieces prepared from HPNLC treated whole melons were negative for the pathogens both by direct plating and by enrichment, fresh-cut pieces from whole melons treated with hydrogen peroxide (2.5%) were positive. Populations of spoilage microflora (aerobic mesophilic bacteria and yeast and mold) transferred from HPNLC treated whole melons were significantly (p<0.05) less than the populations in fresh-cut pieces from water or H2O2 (2.5%) treated whole melon. The results of this study suggest that HPLNC should be used to decontaminate whole melon surfaces to improve the microbial safety and quality of fresh-cut melons.