Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 2005
Publication Date: November 1, 2005
Citation: Ukuku, D.O., Sapers, G.M., Fett, W.F. 2005. ATP bioluminescence assay for estimation of microbial populations of fresh-cut melon. Journal of Food Protection. 68(11):2427-2432. Interpretive Summary: Fruits and vegetables are frequently in contact with soil, insects, animals, and humans during growing, harvesting, and in the processing plant. Thus, their surfaces are not free from natural contaminants, and by the time they reach the packing house, most fresh produce retain higher populations of microorganisms. Estimation of microbial numbers in foods by conventional microbiological techniques takes at least two to three days, and there is a need for faster methods that can give results in minutes. In this study, we investigated the use of a bioluminescence ATP assay to estimate the population of surface microflora on fresh-cut melon, especially those contaminated with aerobic mesophilic bacteria or yeast and mold. Fresh-cut melons prepared from unsanitized and sanitized whole melon were examined for total ATP. The results were compared to fresh-cut pieces contaminated with yeast and mold. Differences in total ATP and Plate count numbers were noted based on the type of treatment used for the whole or fresh-cut melon. ATP and plate count values determined from all fresh-cut melons were higher in contaminated fresh-cut pieces, followed by fresh-cut pieces from unsanitized whole melon and sanitized whole melon, respectively. Based on the results of this study, the bioluminescence ATP assay is a good tool for monitoring microbiological safety of fresh-cut melons after preparation and during refrigerated storage.
Technical Abstract: The level of sanitation during harvest, processing, shipping and at retail outlets as well as the initial microbiological quality of harvested fruit are of primary importance to the shelf-stability and safety of their fresh-cut products. Research was undertaken to investigate the use of a bioluminescence ATP assay to estimate the population of surface microflora on fresh-cut melon contaminated with aerobic mesophilic bacteria or yeast and mold isolated from cantaloupe or honeydew whole melon surfaces. ATP and plate count values were compared for uninoculated fresh-cut melons as well as pieces inoculated with aerobic mesophilic bacteria or yeast and mold at 2 to 5 log10 CFU/g. Plate counts for aerobic bacteria on uninoculated fresh-cut cantaloupe, given no sanitizing treatment, averaged 3.42 log10 CFU/g corresponding to ATP values of 5.40 log10 ATP fg/g. Plate counts for aerobic bacteria on uninoculated fresh-cut honeydew, given no sanitizing treatment, averaged 1.97 log10 CFU/g corresponding to ATP values of 3.94 log10 ATP fg/g. Uninoculated fresh-cut pieces prepared from cantaloupe or honeydew melons sanitized with either chlorine (200 ppm) or hydrogen peroxide (2.5%) had similar ATP values (3.5 log10 ATP fg/g corresponding to 1.6 log10 CFU/g aerobic bacteria for cantaloupes and 2.9 log10 ATP fg/g for 0.48 CFU/g aerobic bacteria for fresh-cut honeydew). ATP values for fresh-cut cantaloupe inoculated with aerobic mesophiles at 4.87 log10 CFU/g and fresh-cut honeydew pieces at 3.27 log10 CFU/g were 5.83 log10 ATP fg/g and 4.17 log10 ATP fg/g, respectively. Fresh-cut pieces inoculated with yeast and mold had higher ATP values than those inoculated with aerobic mesophilic bacteria at comparable population densities. Positive linear correlations for ATP levels and bacterial populations were found for fresh-cut cantaloupe (r2 = 0.989) and honeydew (r2 = 0.954) inoculated with aerobic mesophilic bacteria with total bacterial populations from 4.5 to 7.0 log10 CFU/g. Results of this study indicate that the bioluminescence ATP assay can be used to monitor total microflora on fresh-cut melon after preparation and during storage for quality control purposes or HACCP.