Survival of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in cranberry juice concentrates at different oBrix levels

Survival of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes was evaluated in cranberry juice concentrates to determine if a 5-log reduction could be achieved without any other treatment. Inactivation at 0 degrees C in concentrates with different oBrix levels was determined for a five-strain composite of the individual pathogens in two physiological states. In concentrates at 18 to 46 oBrix (pH 2.2 to 2.5), all three pathogens (stationary-phase or acid-adapted cells) showed at least a 5-log reduction after a 6- or 24-h incubation. At 14 oBrix (pH 2.5), a reduction greater than 5 log was obtained for L. monocytogenes and Salmonella after up to 24 h of incubation, but for E. coli O157:H7, 96 h of incubation was needed to consistently obtain a reduction greater than 5 log. All three pathogens in the stationary phase survived longer than in the acid-adapted phase under the same conditions. The most resistant was stationary-phase E. coli O157:H7, and the most sensitive was acid-adapted L. monocytogenes. The rate of pathogen destruction increased with increasing oBrix level of the juice concentrate, which suggests that concentrated acids and/orsome intrinsic compounds may play an important role in the bactericidal effects of cranberry juice concentrates.     

Inactivation of Shiga toxin-producing Escherichia coli in single-strength lemon and lime juices containing preservatives

The objective of this study was to determine the inactivation of non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes in comparison with O157 STEC in commercially produced, shelf-stable lemon and lime juices. The present validation tests confirmed that storage of the juices containing preservatives at room temperatures (22°C) for 3 days (72 h) ensures a >6-log reduction of O26, O45, O103, O111, O121, O145, and O157 STEC. These results demonstrate that non-O157 STEC had survival abilities comparable to those of E. coli O157:H7 strains in acidic food products such as lemon and lime juices (pH 2.5 ± 0.1); therefore, the storage conditions deemed to inactivate E. coli O157:H7 similarly inactivate the non-O157 serotypes.     

Effect of low-temperature, high-pressure treatment on the survival of Escherichia coli O157:H7 and Salmonella in unpasteurized fruit juices

The destructive effect of high pressure (615 MPa) combined with low temperature (15 degrees C) on various strains of Escherichia coli O157:H7 and various serovars of Salmonella in grapefruit, orange, apple, and carrot juices was investigated. The three-strain cocktail of E. coli O157:H7 (SEA13B88, ATCC 43895, and 932) was found to be most sensitive in grapefruit juice (8.34-log reduction) and least in apple juice (0.41-log reductions) when pressurized at 615 MPa for 2 min at 15 degrees C. Correspondingly, no injured survivor was detected in grapefruit and carrot juices under similar treatment conditions. No Salmonella spp. were detected in a 2-min pressure treatment (615 MPa, 15 degrees C) of grapefruit and orange fruit juices. Except for Enteritidis, all four serovars tested in the present study have viability loss of between 3.92- and 5.07-log reductions when pressurized in apple juice at 615 MPa for 2 min at 15 degrees C. No injured cells were recovered from grapefruit and orange juices, whereas the same treatment demonstrated reduction in numbers of Salmonella serovars Agona and Muenchen in apple juices and to a lesser extent with Typhimurium, Agona, and Muenchen in carrot juice. The present study demonstrated that low-temperature, high-pressure treatment has the potential to inactivate E. coli O157:H7 strains and different Salmonella spp. in different fruit juices.     

Survival of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella in juice concentrates

The survival of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella was studied in apple, orange, pineapple, and white grape juice concentrates and banana puree. Pouches of juice concentrate or puree were inoculated with pathogens at a level > or = 10(3) CFU/g and stored at -23 degrees C (-10 degrees F). Pathogen survival was monitored at 6 and 24 h, once a week for four consecutive weeks, and biweekly thereafter until 12 weeks. When pathogens were not detectable by direct plating, samples were enriched in universal preenrichment broth for 72 h and plated on selective media. Results showed that E. coli O157:H7, L. monocytogenes, and Salmonella were recoverable from all five concentrates through 12 weeks of storage at -23 degrees C.     

High-pressure resistance variation of Escherichia coli O157:H7 strains and Salmonella serovars in tryptic soy broth, distilled water, and fruit juice

The effect of high pressure on the log reduction of six strains of Escherichia coli O157:H7 and five serovars of Salmonella enterica was investigated in tryptic soy broth, sterile distilled water, and commercially sterile orange juice (for Salmonella) and apple cider (for E. coli). Samples were subjected to high-pressure processing treatment at 300 and 550 MPa for 2 min at 6 degrees C. Samples were plated onto tryptic soy agar directly after pressurization and after being held for 24 h at 4 degrees C. At 300 MPa, little effect was seen on E. coli O157:H7 strains, while Salmonella serovars varied in resistance, showing reductions between 0.26 and 3.95 log CFU/ml. At 550 MPa, E. coli O157:H7 strains exhibited a range of reductions (0.28 to 4.39 log CFU/ml), while most Salmonella populations decreased beyond the detection limit (> 5-log CFU/ml reduction). The most resistant strains tested were E. coli E009 and Salmonella Agona. Generally, bacterial populations in fruit juices showed larger decreases than did populations in tryptic soy broth and distilled water. E. coli O157:H7 cultures held for 24 h at 4 degrees C after treatment at 550 MPa showed a significant log decrease as compared with cultures directly after treatment (P < or = 0.05), while Salmonella serovars did not show this significant decrease (P > 0.05). All Salmonella serovars tested in orange juice treated at 550 MPa for 2 min at 6 degrees C and held for 24 h showed a > 5-log decrease, while E. coli O157:H7 strains require a higher pressure, higher temperature, longer pressurization, or a chemical additive to achieve a 5-log decrease.     

Validation of apple cider pasteurization treatments against Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes.

Time and temperature pasteurization conditions common in the Wisconsin cider industry were validated using a six-strain cocktail of Escherichia coli O157:H7 and acid-adapted E. coli O157:H7 in pH- and degrees Brix-adjusted apple cider. Strains employed were linked to outbreaks (ATCC 43894 and 43895, C7927, and USDA-FSIS-380-94) or strains engineered to contain the gene for green fluorescent protein (pGFP ATCC 43894 and pGFP ATCC 43889) for differential enumeration. Survival of Salmonella spp. (CDC 0778. CDC F2833, and CDC H0662) and Listeria monocytogenes (H0222, F8027, and F8369) was also evaluated. Inoculated cider of pH 3.3 or 4.1 and 11 or 14 degrees Brix was heated under conditions ranging from 60 degrees C for 14 s to 71.1 degrees C for 14 s. A 5-log reduction of nonadapted and acid-adapted E. coli O157:H7 was obtained at 68.1 degrees C for 14 s. Lower temperatures, or less time at 68.1 degrees C, did not ensure a 5-log reduction in E. coli O157:H7. A 5-log reduction was obtained at 65.6 degrees C for 14 s for Salmonella spp. L. monocytogenes survived 68.1 degrees C for 14 s, but survivors died in cider within 24 h at 4 degrees C. Laboratory results were validated with a surrogate E coli using a bench-top plate heat-exchange pasteurizer. Results were further validated using fresh unpasteurized commercial ciders. Consumer acceptance of cider pasteurized at 68.1 degrees C for 14 s (Wisconsin recommendations) and at 71.1 degrees C for 6 s (New York recommendations) was not significantly different. Hence, we conclude that 68.1 degrees C for 14 s is a validated treatment for ensuring adequate destruction of E. coli O157:H7, Salmonella spp., and L. monocytogenes in apple cider.     

Death of Salmonella,Escherichia coli O157:H7, and Listeria monocytogenes in garlic butter as affected by storage temperature

Garlic is known to have antimicrobial activity against several spoilage and pathogenic bacteria. However, the fate of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes in garlic butter has not been reported. This study was undertaken to determine the viability of these organisms in garlic butter as affected by the type of raw minced garlic added to the butter, storage temperature, and storage time. Unsalted butter at 40 degrees C was combined with raw minced jumbo, elephant, or small-cloved garlic at a 4:1 butter/garlic ratio (wt/wt), inoculated with mixed-strain suspensions of Salmonella, E. coli O157:H7, or L monocytogenes, and stored at 4.4, 21, or 37 degrees C for up to 48 h. All pathogens retained their viability at 4.4 degrees C, regardless of the presence of garlic. The addition of garlic to butter enhanced the rates of inactivation of all three pathogens at 21 and 37 degrees C. The most rapid decline in pathogen populations was observed at 37 degrees C. The inactivation of L. monocytogenes occurred more slowly than did that of Salmonella or E. coli O157:H7. The inactivation of Salmonella and L. monocytogenes was more rapid in jumbo garlic butter than in elephant or small-cloved garlic butter. It is concluded that Salmonella, E. coli O157:H7, and L. monocytogenes did not grow in unsalted butter, with or without garlic added (20%, wt/wt), when inoculated products were stored at 4.4, 21, and 37 degrees C for up to 48 h.     

Inactivation of Escherichia coli O157:H7 and Salmonella in Apple Cider and Orange Juice Treated with Combinations of Ozone, Dimethyl Dicarbonate, and Hydrogen Peroxide

ABSTRACT: Inactivation of Escherichia coli O157:H7 and Salmonella in apple cider and orange juice treated with ozone in combination with antimicrobials was evaluated. E. coli O157:H7 or Salmonella was suspended in cider and orange juice, and ozone was pumped into juices (4°C) containing dimethyl dicarbonate (DMDC; 250 or 500 ppm) or hydrogen peroxide (300 or 600 ppm) for up to 90 min (study 1) or 60 min followed by 24-h storage at 4°C (study 2). Study 1: No combination of treatments resulted in a 5-log colony-forming units (CFU) /mL reduction of either pathogen. Study 2: All combinations of antimicrobials plus ozone treatments, followed by refrigerated storage, caused greater than a 5-log CFU/mL reduction, except ozone/DMDC (250 ppm) treatment in orange juice. Ozone treatment in combination with DMDC or hydrogen peroxide followed by refrigerated storage may provide an alternative to thermal pasteurization to meet the 5-log reduction standard in cider and orange juice.     

Reduction of Escherichia coli O157:H7 and Salmonella in ground beef using lactic acid bacteria and the impact on sensory properties

Studies were conducted to determine whether four strains of lactic acid bacteria (LAB) inhibited Escherichia coli O157: H7 and Salmonella in ground beef at 5 degrees C and whether these bacteria had an impact on the sensory properties of the beef. The LAB consisted of frozen concentrated cultures of four Lactobacillus strains, and a cocktail mixture of streptomycin-resistant E. coli O157:H7 and Salmonella were used as pathogens. Individual LAB isolates at 10(7) CFU/ml were added to tryptic soy broth containing a pathogen concentration of 10(5) CFU/ml. Samples were stored at 5 degrees C, and pathogen populations were determined on days 0, 4, 8, and 12. After 4 days of storage, there were significant differences in numbers of both pathogens exposed to LAB isolates NP 35 and NP 3. After 8 and 12 days of storage, all LAB reduced populations of both pathogens by an average of 3 to 5 log cycles. A second study was conducted in vacuum-packaged fresh ground beef. The individual LAB isolates resulted in an average difference of 1.5 log cycles of E. coli O157:H7 after 12 days of storage, and Salmonella populations were reduced by an average of 3 log cycles. Following this study, a mixed concentrated culture was prepared from all four LAB and added to ground beef inoculated with pathogen at 10(8) CFU/g. After 3 days of storage, the mixed culture resulted in a 2.0-log reduction in E. coli O157:H7 compared with the control, whereas after 5 days of storage, a 3-log reduction was noted. Salmonella was reduced to nondetectable levels after day 5. Sensory studies on noninoculated samples that contained LAB indicated that there were no adverse effects of LAB on the sensory properties of the ground beef. This study indicates that adding LAB to raw ground beef stored at refrigeration temperatures may be an important intervention for controlling foodborne pathogens.     

Inactivation of Escherichia coli O157:H7 in orange juice using a combination of high pressure and mild heat

The effect of high pressure on the survival of a pressure-resistant strain of Escherichia coli O157:H7 (NCTC 12079) in orange juice was investigated over the pH range 3.4 to 5.0. The pH of commercial, sterile orange juice was adjusted to 3.4, 3.6, 3.9, 4.5, or 5.0. The juice was then inoculated with 10(8) CFU ml(-1) of E. coli O157:H7. The inoculated orange juice was subjected to pressure treatments of 400, 500, or 550 MPa at 20 degrees C or 30 degrees C to determine the conditions that would give a 6-log10 inactivation of E. coli O157:H7. A pressure treatment of 550 MPa for 5 min at 20 degrees C produced this level of kill at pH 3.4, 3.6, 3.9, and 4.5 but not at pH 5.0. Combining pressure treatment with mild heat (30 degrees C) did result in a 6-log10 inactivation at pH 5.0. Thus, the processing conditions (temperature and time) must be considered when pressure-treating orange juice to ensure microbiological safety.     

Thermal inactivation studies of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in ready-to-eat chicken-fried beef patties

Thermal inactivation studies were used to determine the D- and z-values of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in ready-to-eat chicken-fried beef patties. Inoculated meat was packaged in sterile bags, which were immersed in a circulated water bath and held at 55, 57.5, 60, 62.5, 65, 67.5, and 70 degrees C for different lengths of time. D- and z-values were determined with a linear regression model. Average D-values at temperatures 55 to 70 degrees C were 27.62 to 0.04 min for E. coli 0157:H7, 67.68 to 0.22 min for Salmonella, and 81.37 to 0.31 min for L. monocytogenes. The z-values were 5.2 degrees C for E. coli O157:H7, 6.0 degrees C for Salmonella, and 6.1 degrees C for L. monocytogenes. The results of this study can be used by food processors to validate their processes and help eliminate pathogenic bacteria associated with chicken-fried beef products.     

Determination of 5-log reduction times for food pathogens in acidified cucumbers during storage at 10 and 25 degrees C

Outbreaks of acid-resistant foodborne pathogens in acid foods with pH values below 4.0, including apple cider and orange juice, have raised concerns about the safety of acidified vegetable products. For acidified vegetable products with pH values between 3.3 and 4.6, previous research has demonstrated that thermal treatments are needed to achieve a 5-log reduction in the numbers of Escherichia coli O157:H7, Listeria monocytogenes, or Salmonella enterica. For some acidified vegetable products with a pH of 3.3 or below, heat processing can result in unacceptable product quality. The purpose of this study was to determine the holding times needed to achieve a 5-log reduction in E. coli O157:H7, L. monocytogenes, and S. enterica strains in acidified vegetable products with acetic acid as the primary acidulant, a pH of 3.3 or below, and a minimum equilibrated temperature of 10 degrees C. We found E. coli O157:H7 to be the most acid-resistant microorganism for the conditions tested, with a predicted time to achieve a 5-log reduction in cell numbers at 10 degrees C of 5.7 days, compared with 2.1 days (51 h) for Salmonella or 0.5 days (11.2 h) for Listeria. At 25 degrees C, the E. coli O157:H7 population achieved a 5-log reduction in 1.4 days (34.3 h).     

High pressures in combination with antimicrobials to reduce Escherichia coli O157:H7 and Salmonella Agona in apple juice and orange juice

The effect of high pressure processing in conjunction with the chemical antimicrobials, dimethyl dicarbonate (DMDC), hydrogen peroxide, cinnamic acid, potassium sorbate, and sodium benzoate (NaB) on E. coli O157:H7 strain E009 and Salmonella enterica serovar Agona was investigated in apple juice and orange juice, respectively. Juices were inoculated with approximately 10(6) CFU/ml and subjected to pressures of 550 MPa (E. coli O157:H7 samples) and 400 MPa (Salmonella Agona samples) for 2 min at 6 degrees C (initial temperature). Populations of each pathogen were determined before pressurization, immediately after pressurization, and after samples had been held after treatment for 24 h at 4 degrees C. The most effective treatment for E. coli O157:H7, as determined by plating immediately after pressurization, was 125 ppm of DMDC, which caused a >4.98-log reduction. Other treatments that were significantly different from the sample with no added antimicrobial were 62.5 ppm of DMDC, 300 ppm of hydrogen peroxide, and 500 ppm of NaB, which produced 4.97-, 5.79-, and 3.91-log total reductions, respectively. After 24 h at 4 degrees C, E. coli O157:H7 was undetectable in all treatment groups (and controls). In samples inoculated with Salmonella, the most effective treatment was 62.5 ppm of DMDC, which produced a 5.96-log decrease immediately after pressure treatment. The results for 1,000 ppm of NaB, which produced a 3.26-log decrease, also were significantly different from those for the sample containing no antimicrobials. After 24 h at 4 degrees C, all samples with added antimicrobials had near or more than a 5-log total reduction of Salmonella Agona.     

Survival of Escherichia coli O157:H7 and Salmonella in apple cider and orange juice as affected by ozone and treatment temperature

Inactivation of Escherichia coli O157:H7 and Salmonella in apple cider and orange juice treated with ozone was evaluated. A five-strain mixture of E. coli O157:H7 or a five-serovar mixture of Salmonella was inoculated (7 log CFU/ml) into apple cider and orange juice. Ozone (0.9 g/h) was pumped into juices maintained at 4 degrees C, ambient temperature (approximately 20 degrees C), and 50 degrees C for up to 240 min, depending on organism, juice, and treatment temperature. Samples were withdrawn, diluted in 0.1% peptone water, and surface plated onto recovery media. Recovery of E. coli O157:H7 was compared on tryptic soy agar (TSA), sorbitol MacConkey agar, hemorrhagic coli agar, and modified eosin methylene blue agar; recovery of Salmonella was compared on TSA, bismuth sulfite agar, and xylose lysine tergitol 4 (XLT4) agar. After treatment at 50 degrees C, E. coli O157:H7 populations were undetectable (limit of 1.0 log CFU/ml; a minimum 6.0-log CFU/ml reduction) after 45 min in apple cider and 75 min in orange juice. At 50 degrees C, Salmonella was reduced by 4.8 log CFU/ml (apple cider) and was undetectable in orange juice after 15 min. E. coli O157:H7 at 4 degrees C was reduced by 4.8 log CFU/ml in apple cider and by 5.4 log CFU/ml in orange juice. Salmonella was reduced by 4.5 log CFU/ml (apple cider) and 4.2 log CFU/ml (orange juice) at 4 degrees C. Treatment at ambient temperature resulted in population reductions of less than 5.0 log CFU/ml. Recovery of E. coli O157:H7 and Salmonella on selective media was substantially lower than recovery on TSA, indicating development of sublethal injury. Ozone treatment of apple cider and orange juice at 4 degrees C or in combination with mild heating (50 degrees C) may provide an alternative to thermal pasteurization for reduction of E. coli O157:H7 and Salmonella in apple cider and orange juice.     

Survival of Salmonella spp. and Escherichia coli O157:H7 on fresh and frozen strawberries

For maximum shelf life, fresh strawberries are harvested directly without washing into retail containers. Frozen berries are usually hulled in the field and washed prior to freezing, sometimes with the addition of sucrose. To determine survival of potential bacterial contaminants, cut or intact surfaces of fresh strawberries were spot inoculated with five- or six-strain cocktails of Salmonella or Escherichia coli O157:H7 (log 7.0 CFU/sample). Inoculated strawberries were dried for 1 h at 24 degrees C and were stored in closed containers at 5 or 24 degrees C. Sliced strawberries with or without added 20% sucrose were inoculated with one of two strains of E. coli O157:H7 and frozen at -20 degrees C. An initial population reduction of approximately 0.5-log cycles was observed on intact but not cut berries after the 1-h drying period. During storage at 24 degrees C for up to 48 h, populations of Salmonella and E. coli O157:H7 did not decline further. When strawberries were stored at 5 degrees C for up to 7 days, populations of both pathogens remained constant on cut surfaces but decreased by 1 - to 2-log cycles on intact surfaces. After 30 days of frozen storage, the population of E. coli O157:H7 had declined by 0.7- to 2.2-log cycles (with and without sucrose, respectively). Results of this study indicate that E. coli O157:H7 and Salmonella are capable of survival but not growth on the surface of fresh strawberries throughout the expected shelf life of the fruit and can survive in frozen strawberries for periods of greater than 1 month.     

Inactivation of Escherichia coli O157:H7, Salmonella enterica serotype enteritidis,and Listeria monocytogenes on lettuce by hydrogen peroxide and lactic acid and by hydrogen peroxide with mild heat

Iceberg lettuce is a major component in vegetable salad and has been associated with many outbreaks of foodborne illnesses. In this study, several combinations of lactic acid and hydrogen peroxide were tested to obtain effective antibacterial activity without adverse effects on sensory characteristics. A five-strain mixture of Escherichia coli O157:H7, Salmonella enterica serotype Enteritidis, and Listeria monocytogenes was inoculated separately onto fresh-cut lettuce leaves, which were later treated with 1.5% lactic acid plus 1.5% hydrogen peroxide (H2O2) at 40 degrees C for 15 min, 1.5% lactic acid plus 2% H2O2 at 22 degrees C for 5 min, and 2% H2O2 at 50 degrees C for 60 or 90 s. Control lettuce leaves were treated with deionized water under the same conditions. A 4-log reduction was obtained for lettuce treated with the combinations of lactic acid and H2O2 for E. coli O157:H7 and Salmonella Enteritidis, and a 3-log reduction was obtained for L. monocytogenes. However, the sensory characteristics of lettuce were compromised by these treatments. The treatment of lettuce leaves with 2% H2O2 at 50 degrees C was effective not only in reducing pathogenic bacteria but also in maintaining good sensory quality for up to 15 days. A < or = 4-log reduction of E. coli O157:H7 and Salmonella Enteritidis was achieved with the 2% H2O2 treatment, whereas a 3-log reduction of L. monocytogenes was obtained. There was no significant difference (P > 0.05) between pathogen population reductions obtained with 2% H2O2 with 60- and 90-s exposure times. Hydrogen peroxide residue was undetectable (the minimum level of sensitivity was 2 ppm) on lettuce surfaces after the treated lettuce was rinsed with cold water and centrifuged with a salad spinner. Hence, the treatment of lettuce with 2% H2O2 at 50 degrees C for 60 s is effective in initially reducing substantial populations of foodborne pathogens and maintaining high product quality.     

Determination of 5-log pathogen reduction times for heat-processed, acidified vegetable brines

Recent outbreaks of acid-resistant food pathogens in acid foods, including apple cider and orange juice, have raised concerns about the safety of acidified vegetable products. We determined pasteurization times and temperatures needed to assure a 5-log reduction in the numbers of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella strains in acidified cucumber pickle brines. Cocktails of five strains of each pathogen were (separately) used for heat-inactivation studies between 50 and 60 degrees C in brines that had an equilibrated pH value of 4.1. Salmonella strains were found to be less heat resistant than E. coli O157:H7 or L. monocytogenes strains. The nonlinear killing curves generated during these studies were modeled using a Weibull function. We found no significant difference in the heat-killing data for E. coli O157:H7 and L. monocytogenes (P = 0.9709). The predicted 5-log reduction times for E. coli O157:H7 and L. monocytogenes were found to fit an exponential decay function. These data were used to estimate minimum pasteurization times and temperatures needed to ensure safe processing of acidified pickle products and show that current industry pasteurization practices offer a significant margin of safety.     

Efficiency of sodium hypochlorite, fumaric acid, and mild heat in killing native microflora and Escherichia coli O157:H7, Salmonella typhimurium DT104, and Staphylococcus aureus attached to fresh-cut lettuce

The effect of the disinfectant sodium hypochlorite (NaClO), with or without mild heat (50 degrees C) and fumaric acid, on native bacteria and the foodborne pathogens Staphylococcus aureus, Escherichia coli O157:H7, and Salmonella Typhimurium DT104 attached to iceberg lettuce leaves was examined. The retail lettuce examined consistently harbored 6 to 7 log CFU/g of native bacteria throughout the study period. Inner leaves supported 1 to 2 log CFU/g fewer bacteria than outer leaves. About 70% of the native bacterial flora was removed by washing five times with 0.85% NaCl. S. aureus, E. coli, and Salmonella allowed to attach to lettuce leaves for 5 min were more easily removed by washing than when allowed to attach for 1 h or 2 days, with more S. aureus being removed than E. coli or Salmonella Typhimurium. An increase of time for attachment of pathogens from 5 min to 2 days leads to decreased efficiency of the washing and sanitizing treatment. Treatment with fumaric acid (50 mM for 10 min at room temperature) was the most effective, although it caused browning of the lettuce, with up to a 2-log reduction observed. The combination of 200 ppm of sodium hypochlorite and mild heat treatment at 50 degrees C for 1 min reduced the pathogen populations by 94 to 98% (1.2- to 1.7-log reduction) without increasing browning.     

Survival of Escherichia coli O157:H7 during storage in pressure-treated orange juice.

The effect of a high-pressure treatment on the survival of a pressure-resistant strain of Escherichia coli O157:H7 (NCTC 12079) in orange juice during storage at 3 degrees C was investigated over the pH range of 3.4 to 5.0. The pH of shelf-stable orange juice was adjusted to 3.4, 3.6, 3.9, 4.5, and 5.0 and inoculated with 10(8) CFU ml(-1) of E. coli O157:H7. The orange juice was then pressure treated at 400 MPa for 1 min at 10 degrees C or was held at ambient pressure (as a control). Surviving E. coli O157:H7 cells were enumerated at 1-day intervals during a storage period of 25 days at 3 degrees C. Survival of E. coli O157:H7 during storage was dependent on the pH of the orange juice. The application of high pressure prior to storage significantly increased the susceptibility of E. coli O157:H7 to high acidity. For example, after pressure treatment, the time required for a 5-log decrease in cell numbers was reduced from 13 to 3 days at pH 3.4, from 16 to 6 days at pH 3.6, and from >25 to 8 days at pH 3.9. It is evident that the use of high-pressure processing of orange juice in order to increase the juice's shelf-life and to inactivate pathogens has the added advantage that it sensitizes E. coli O157:H7 to the high acid conditions found in orange juice, which results in the survival of significantly fewer E. coli O157:H7 during subsequent refrigerated storage.     

Toward validation of process criteria for high-pressure processing of orange juice with predictive models

Mathematical models were developed to predict time to inactivation (TTI) by high-pressure processing of Salmonella in Australian Valencia orange juice (pH 4.3) and navel orange juice (pH 3.7) as a function of pressure magnitude (300 to 600 MPa) and inoculum level (3 to 7 log CFU/ml). For each model, the TTI was found to increase with increasing inoculum level and decrease with increasing pressure magnitude. The U.S. Food and Drug Administration Juice Hazard Analysis and Critical Control Point Regulation requires fruit juice processors to include control measures that produce a 5-log reduction of the pertinent microorganism of public health significance in the juice. To achieve a 5-log reduction of Salmonella in navel orange juice at 20 degrees C, the models predicted hold times of 198, 19, and 5 s at 300, 450, and 600 MPa, respectively. In Valencia orange juice at 20 degrees C, a 5-log reduction of Salmonella was achieved in 369, 25, and 5 s at 300, 450, and 600 MPa, respectively. At pressures below 400 MPa, Salmonella was more sensitive to pressure in the more acidic conditions of the navel orange juice and TTIs were shorter. At higher pressures, little difference in the predicted TTI was observed. Refrigerated storage (4 degrees C) of inoculated navel orange juice treated at selected pressure/time/inoculum combinations showed that under conditions in which viable Salmonella was recovered immediately after high-pressure processing, pressure-treated Salmonella was susceptible to the acidic environment of orange juice or to chill storage temperature. These TTI models can assist fruit juice processors in selecting processing criteria to achieve an appropriate performance criterion with regard to the reduction of Salmonella in orange juice, while allowing for processing flexibility and optimization of high-pressure juice processing.