Distribution of E. coli (ATCC 25922) on Surfaces of Inoculated Apples Before and After Washing with 5% H2O2 at 50°C
24 h after inoculation
72 h after inoculation
Skin except at calyx and stem ends 4.77 2.05 4.37 1.63
Skin at calyx end of core 7.26 5.20 6.79 4.46
Skin on stem end of core 6.63 5.06 5.61 4.89
From Sapers, G.M. et al., J. Food Sci., 65, 529, 2000. Reprinted with permission.
relatively inaccessible stem and blossom ends of the apples, or were internalized within the latter region, survived washing while E. coli attached elsewhere on the apple surface were readily inactivated (Table 17.3). Greater efficacy was obtained when the apples were washed by full immersion in a sanitizing solution with vigorous agitation .
Gagliardi et al.  examined commercial practices for washing melons produced in the Rio Grande River Valley of Texas. They reported little or no reduction in the population of coliforms, fecal coliforms, enterococci, and fecal enterococci in cantaloupes and honeydew melons that were washed with water in a tank and then spray rinsed on a conveyor line. Use of chlorinated water in the secondary rinse appeared to reduce the populations of fecal coliforms and fecal enterococci but not total coliforms and enterococci. Laboratory-scale washing studies with cantaloupes that had been dip-inoculated with Salmonella Stanley or a nonpathogenic E. coli (ATCC 25922) demonstrated that the population reductions obtained by immersion of the melons in 200 ppm Cl2 or 5% H2O2 decreased as the time interval between inoculation and washing increased from 24 hours to 5 days [69,70]. However, the efficacy of these treatments in inactivating L. monocytogenes on inoculated cantaloupes was not dependent on the length of storage between inoculation and treatment . Sapers et al. obtained minimal inactivation of E. coli B-766 (a surrogate for S. Poona) when dip-inoculated cantaloupes were immersed in 300 ppm Cl2 for 3 minutes . Apparently, cantaloupes are especially difficult to disinfect, even if fully immersed in the sanitizing solution. This may be due to the movement, attachment, and possible biofilm formation by the targeted bacteria within inaccessible pores in the netting so that contact between the sanitizing solution and the attached bacteria is minimal. This is borne out by the success of treatments with 5% H2O2 at 70°C or near boiling water where heat penetration contributes to the efficacy of the antimicrobial treatment  (see Chapter 10). Such treatments can greatly reduce the risk of transfer of human pathogens from the rind surface to the flesh during fresh-cut processing.
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