Conventional and experimental washing formulations were applied with a commercial flatbed brush washer under conditions representative of commercial practice to determine their efficacy in decontaminating apples inoculated with a nonpathogenic Escherichia coli strain. Golden Delicious apples (18 kg) inoculated with E. coli were mixed with approximately 109 kg of uninoculated Fuji apples (distinctly different in appearance) in a wet dump tank containing 1,325 liters of water at 20 degrees C for 15 min. The combined apples were washed in a flatbed brush washer with the following washing solutions: water at 20 degrees C, water at 50 degrees C, 200 ppm of chlorine (pH 6.4) at 20 degrees C, 8% trisodium phosphate at 20 degrees C, 8% trisodium phosphate at 50 degrees C, 5% hydrogen peroxide at 20 degrees C, 5% hydrogen peroxide at 50 degrees C, 1% APL Kleen 245 at 50 degrees C, and two-stage washing treatments using the combination of 1% APL Kleen 245 at 20 or 50 degrees C followed by 5% hydrogen peroxide at 35 or 50 degrees C. None of the washing treatments tested under the conditions of this experiment significantly reduced the E. coli populations on the inoculated apples or in cider made from these apples, probably as a consequence of the inability of this washing system to inactivate or remove the bacterial cells in inaccessible calyx and stem areas of apples. These results are important because they demonstrate the need for new fruit washing technology that can overcome this limitation. Also, there was no significant cross-contamination of the Fuji apples in the dump tank. Significant cross-contamination of cider, made with uninoculated apples, occurred in the hammer mill and/or the press cloth when these units were not sanitized following a trial with inoculated apples.

The thermotolerance of E. coli O157:H7 cells (strain 380-94) heated in pepperoni is reported. Information on the pattern of thermal inactivation of E. coli O157:H7 in pepperoni was applied in the development of heating processes designed to reduce E. coli O157:H7 numbers therein by 5 log 10 units.The identification of fermented meat as a vehicle of infection for Escherichia coli O157:H7 (4) has led to the development of heat treatments for such products (3,8,10) such that a 5-log 10 -unit reduction in E. coli O157:H7 numbers can be achieved during processing. Fermented meat had traditionally relied on its low pH status as its primary preservative mechanism; however, E. coli O157:H7 has been shown to be unusually resistant to inactivation at low pHs (9, 12, 13). Thus, it is imperative that this factor be borne in mind when heat treatments are designed. Previous studies involving E. coli O157:H7 (5, 16) have shown that cross-protection, i.e., preadaptation to one stress encountered in the environment, e.g., acid, can lead to enhanced resistance to a different, and possibly previously unencountered, stress, e.g., heat. Therefore, the possibility that cross-protection could occur must be considered in the development of thermal inactivation protocols. This study aimed to elucidate the effects of prior acid adaptation and final product pH on the thermotolerance of E. coli O157:H7 in pepperoni. The information derived was used to develop a commercially applicable postfermentation heating process capable of inducing a 5-log 10 -unit reduction in E. coli O157:H7 numbers.E. coli O157:H7 (strain 380-94) was obtained from the Centers for Disease Control and Prevention, Atlanta, Ga., maintained on tryptone soya agar (TSA; Oxoid, Basingstoke, England) at 4°C, and recultured monthly. Inocula were prepared by adding one loopful of culture from TSA into (i) 50 ml of brain heart infusion broth (BHI; Oxoid) (0.2% [wt/vol] glucose) or (ii) 50 ml of BHI supplemented with 1% (wt/vol) glucose (1.2% [wt/vol] glucose). Cultures were grown at 37°C (18 h) to provide non-acid-adapted organisms and acidadapted organisms, respectively (2). pH was estimated using a model 210 pH meter (Orion Research Corp., Boston, Mass.). Pepperoni batters were prepared and fermented by the following modifications of the method previously described (18). Meat mixtures were inoculated with acid-adapted and nonacid-adapted E. coli O157:H7, as previously outlined, and stored at 4°C overnight. The meat mixtures were then incorporated into standard-and low-pH batter mixes. The standardfinal-pH product was formulated to ferment to a final pH of 4.8 by the addition of 0.625% sodium nitrite (0.01%), Pediococcus spp. starter culture (0.028%), sodium ascorbate (0.048%), spice mix (0.302%), dextrose (0.625%), mustard flour (1.5%), and salt (2.5%) (all wt/wt) with other ingredients previously described (18). The low-final-pH product was formulated to ferment to a final pH of 4.4 by the addition of dextrose at 1% (wt/wt). Approximately 12 sausages per batch (150 by 30 mm...

The survival of Escherichia coli O157:H7 in the presence of one of two plant pathogens, Penicillium expansum and Glomerella cingulata, in wounds on apples was observed during 14 days storage at room temperature (RT) and at 4 degrees C. The aim of this work was to determine if changes in apple physiology caused by the proliferation of fungal decay organisms would foster the survival of E. coli O157:H7. Trials were performed where (A) plant pathogens (4 log10 spores) were added to apple wounds 4 days before the wounds were inoculated with E. coli O157:H7 (3 log10 CFU g(-1) apple) (both RT and 4 degrees C storage), (B) plant pathogens and E. coli O157:H7 were added on the same day (both RT and 4 degrees C storage), and (C) E. coli O157:H7 was added 2 days (RT storage) and 4 days (4 degrees C storage) before plant pathogens. In all trials E. coli O157:H7 levels generally declined to<1 log10 at 4 degrees C storage, and in the presence of P. expansum at 4 degrees C or RT. However, in the presence of G. cingulata at RT E. coli O157:H7 numbers increased from 3.18 to 4.03 log10 CFU g(-1) in the apple wound during trial A, from 3.26 to 6.31 log10 CFU g(-1) during trial B, and from 3.22 to 6.81 log10 CFU g(-1) during trial C. This effect is probably a consequence of the attendant rise in pH from 4.1 to approximately 6.8, observed with the proliferation of G. cingulata rot. Control apples (inoculated with E. coli O157:H7 only) were contaminated with opportunistic decay organisms at RT during trials A and B, leading to E. coli O157:H7 death. However, E. coli O157:H7 in control apples in trial C, where no contamination occurred, increased from 3.22 to 5.97 log10 CFU g(-1). The fact that E. coli O157:H7 can proliferate in areas of decay and/or injury on fruit highlights the hazards associated with the use of such fruit in the production of unpasteurized juice.