Bioluminescence ATP assay for estimating total plate counts of surface microflora of whole cantaloupe and determining efficacy of washing treatments

The surface microflora of cantaloupes were estimated using a bioluminescenc e ATP assay, and results were compared to plate count data. Cantaloupes wer e treated as follows: (i) water washed, or (ii) washed in solutions of sodi um hypochlorite (1,000 mg/liter) or hydrogen peroxide (5%) for 5 min. Biolu minescence ATP assay results showed differences in ATP level/cm(2) of canta loupes dipped in chlorine or hydrogen peroxide solution; ATP levels in thes e washed samples were lower than in controls due to antimicrobial action of the treatments on the cantaloupe surface. Linear correlations were found b etween the bioluminescence ATP assay and aerobic plate counts of unwashed c antaloupe (r(2) = 0.995) and those washed with water (r(2) = 0.990) determi ned before storage. Lower correlations between the bioluminescence ATP assa y and the aerobic plate counts were observed on cantaloupes stored for 120 h at 20 degreesC (r(2) = 0.751) than at 4 degreesC (r(2) = 0.980) without w ashing treatment. Lower correlation at 20 degreesC may be the result of clu sters or growth that occurred in chains. ATP levels of washed cantaloupes c orrelated well with bacterial plate counts (r(2) = 0.999). A reliable minim um detectable threshold using the bioluminescence ATP assay was established at 3 log(10) fg/cm(2) corresponding to 4 log(10) CFU/cm(2). Bioluminescenc e ATP assay is not recommended for washed samples where the microbial load is near or below the threshold. Therefore, the bioluminescence ATP assay wi ll be recommended for quick estimation of total microbial load on cantaloup e surfaces where the population is expected to exceed this threshold. The a ssay can save the industry time by eliminating the required incubation requ ired by the conventional methods.