Efficacy of selected chemicals and electron beam irradiation for destroying Escherichia coli 0157:H7 and Salmonella on cantaloupe skin
This study evaluated the efficacy of citric acid (1, 2, or 3% CA) alone or combined with hydrogen peroxide (5% HP), sodium lauryl sulfate (1% SLS), and irradiation for destroying Escherichia coli 0157:H7 and Salmonella spp. on the outer rind surface of cantaloupe. Cantaloupe rinds were cut into 2.5 cm2 pieces and inoculated with either a five strain mixture of nalidixic acid resistant Salmonella spp. or E. coli to give [difference] 107 CFU/ rind. Inoculated rinds were dipped for 2.0 min in 500 ml of water (control) or sanitizer solutions at 230C. Samples treated with combinations of HP + SLS alone or combined with 1% CA were irradiated at 0.0, 0.5, and 1.0 kGy. Non-irradiated and irradiated cantaloupe rinds were homogenized in buffered peptone water (100 ml). Samples of homogenate were serially diluted and plated into Bismuth Sulfite agar and MacConkey Sorbitol agar, both containing nalidixic acid. All inoculated agar plates were incubated at 350C for 48 h. Salmonella and E. coli survivors were enumerated following incubation and expressed as log CFU/ rind. Compared to the water dipped control, exposure of rinds to 5% HP reduced populations of Salmonella and E. coli by 2.7 and 2.83 log CFU/rind, respectively. A combination of 5% HP and 1% SLS decreased populations of Salmonella and E. coli by 3.37 and 2.98 log. Further reductions were achieved by combining 5% HP and 1% CA with 1% SLS; populations of Salmonella and E. coli decreased by 3.9 and 4.0 log, respectively. Combination of 0.5 kGy irradiation with a chemical solution of HP, SLS and CA reduced the numbers by 4.5 and 5.48 log, for Salmonella and E. coli respectively. Irradiation of 1.0 kGy in combination with HP, SLS and CA reduced the population of Salmonella by 5.67 log CFU/rind and by more than 7 log CFU/rind for E. coli. Based on these results, the combined use of acidified HP with an anionic surfactant (SLS) and irradiation has good potential for improving the microbial safety of cantaloupe melons. Further research is needed to determine the effects of these interventions on quality characteristics of melons.