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The acid resistance of Listeria monocytogenes was evaluated: (i) after short (shock) or long-term (adaptation during growth) exposure to reduced (5.5) or neutral (7.2) pH in a liquid (broth) medium or on a solid surface (agar), and (ii) after growth on the surface of ham and turkey slices or in homogenates of these products. Three L. monocytogenes strains (serotypes 1/2a, 1/2b and 4b) were individually inoculated at: (i) 10(4)-10(5)CFU/ml in tryptic soy broth with 0.6% yeast extract (TSBYE) or on tryptic soy agar with 0.6% yeast extract (TSAYE) at pH 7.2 with 1% (+G) or without (-G) glucose of or TSBYE and TSAYE with 0.25% glucose at pH 5.5 (lactic acid) and incubated at 20°C, and (ii) 10(2)-10(3)CFU/cm(2) on ham and turkey slices (pH 6.39-6.42; formulated with potassium lactate and sodium diacetate) or in their homogenates (1:4 and 1:9; representing viscous [slurry] and liquid residues [purge], respectively), and stored at 10°C. The acid resistance of each strain was assessed in TSBYE of pH 3.5 (lactic acid) for strains growing in broth or on agar surfaces, and in TSBYE of pH 1.5 (HCl) for strains growing on ham and turkey slices or in their homogenates. Habituation at pH 5.5 for 3 or 24h at 20°C increased acid (pH 3.5) resistance of all strains compared to the control (pH 7.2). Cells grown on the surface of TSAYE-G (pH 7.2 or 5.5) showed higher resistance than cells grown in broth (TSBYE-G), whereas the opposite was observed for cells grown on TSAYE + G or in TSBYE + G. Growth of L. monocytogenes on meat product slices was markedly slower than in homogenates. Pathogen reductions following exposure to pH 1.5, after 10 and 27days of storage were strain-dependent and in the ranges of 0.5-2.5, 1.3-4.5 and 4.0-7.6 log units for cells grown on product slices in 1:4 and 1:9 homogenates, respectively. The results suggest that L. monocytogenes cells growing on food surfaces or in viscous matrices may show higher resistance to lethal acid conditions than cells growing in liquid substrates., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Escherichia coli O157:H7 attached to beef-contact surfaces found in beef fabrication facilities may serve as a source of cross-contamination. This study evaluated E. coli O157:H7 attachment, survival and growth on food-contact surfaces under simulated beef processing conditions. Stainless steel and high-density polyethylene surfaces (2×5cm) were individually suspended into each of three substrates inoculated (6log CFU/ml or g) with E. coli O157:H7 (rifampicin-resistant, six-strain composite) and then incubated (168h) statically at 4 or 15°C. The three tested soiling substrates included sterile tryptic soy broth (TSB), unsterilized beef fat-lean tissue (1:1 [wt/wt]) homogenate (10% [wt/wt] with sterile distilled water) and unsterilized ground beef. Initial adherence/attachment of E. coli O157:H7 (0.9 to 2.9log CFU/cm(2)) on stainless steel and high-density polyethylene was not affected by the type of food-contact surface but was greater (p<0.05) through ground beef. Adherent and suspended E. coli O157:H7 counts increased during storage at 15°C (168h) by 2.2 to 5.4log CFU/cm(2) and 1.0 to 2.8log CFU/ml or g, respectively. At 4°C (168h), although pathogen levels decreased slightly in the substrates, numbers of adherent cells remained constant on coupons in ground beef (2.4 to 2.5log CFU/cm(2)) and increased on coupons in TSB and fat-lean tissue homogenate by 0.9 to 1.0and 1.7 to 2.0log CFU/cm(2), respectively, suggesting further cell attachment. The results of this study indicate that E. coli O157:H7 attachment to beef-contact surfaces was influenced by the type of soiling substrate and temperature. Notably, attachment occurred not only at a temperature representative of beef fabrication areas during non-production hours (15°C), but also during cold storage (4°C) temperatures, thus, rendering the design of more effective sanitation programs necessary., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Non-intact beef products include beef cuts that have been ground, mechanically tenderized, restructured, or have been injected with solutions to enhance tenderness and/or flavor. This study examined the effects of tenderizing salts and organic acids on thermal inactivation of Escherichia coli O157:H7 in a ground beef model system simulating non-intact beef products. Ground beef (95% lean; 700 g batches) was mixed (2 min) with nothing (C) or solutions (22 ml) of water (WA), calcium ascorbate (CaA, 0.86%; wt/wt), calcium chloride (CaC, 0.23%; wt/wt), acetic acid (AA, 0.3%; v/wt), citric acid (CA, 0.2%; wt/wt), NaCl (NA, 0.5%; wt/wt), and mixtures of CaA/NA, CaC/NA, AA/NA, CA/NA, CaA/CaC/NA, CaA/AA/NA, CaA/CA/NA, CaC/AA/NA and CaC/CA/NA. Samples (30 g) were extruded into test tubes, inoculated (7 log CFU/g) with E. coli O157:H7 (5-strain mixture), and stored (4 degrees C) overnight. Samples were then cooked to 60 degrees C or 65 degrees C, in a water bath, to simulate rare or medium-rare doneness of beef, respectively. Weight, fat and moisture losses, total bacterial (tryptic soy agar) and E. coli O157:H7 (modified eosin methylene blue agar, and modified sorbitol MacConkey agar) populations were determined after inoculation, storage, and cooking. Fat and moisture losses were not affected by treatment and temperature, while weight losses increased at 65 degrees C and in acid treated samples (60 degrees C). E. coli O157:H7 survivors were generally lower (P<0.05) in acid treated than non-acid treated samples. Pathogen counts in samples treated with tenderizers (CaA, CaC) and NA were not different (P> or =0.05) than those of control samples. Thus, inclusion of organic acids in beef tenderizing recipes may help in thermal inactivation of E. coli O157:H7 that may been transferred to the interior of non-intact products during their production.

The objective of this study was to model with logistic regression the growth/no growth interface of different initial inoculation levels (10(1), 10(3) and 10(5) CFU/ml; study 1), or nonadapted vs acid-adapted (study 2) Escherichia coli O157:H7 as influenced by pH, NaCl concentration and incubation temperature. Study 1 was conducted with a mixture of four E. coli O157:H7 strains grown (35 degrees C, 24 h) in tryptic soy broth (TSB). Study 2 was conducted with the same mixture of four E. coli O157:H7 strains grown (35 degrees C, 24 h) in glucose-free TSB with 1% added glucose (final pH 4.83), or in diluted lactic acid meat decontamination runoff fluids (washings; final pH 4.92), or nonadapted cultures prepared in glucose-free TSB (final pH 6.45), or in water washings (final pH 6.87). Parameters included incubation temperature (10-35 degrees C), pH (3.52-7.32), and NaCl concentration (0-10% w/v). Growth responses were evaluated for 60 days turbidimetrically (610 nm) every 5 days in 160 (study 1) and 360 (study 2) combinations in quadruplicate samples, with a microplate reader. The lower the initial inoculum the higher were the minimum pH and a(w) values permitting growth. Differences in the pH and a(w) growth limits among inoculum concentrations increased at 15 and 10 degrees C. Acid-adapted cultures were able to grow at lower pH than nonadapted cultures, while at temperatures below 25 degrees C, growth initiation of nonadapted cultures stopped at higher a(w) compared to acid-adapted cultures for the whole pH range of 3.52 to 7.32. A comparison with available data indicated that our model for acid-adapted E. coli O157:H7 in different environments may provide representative growth probabilities covering both nonadapted and stress-adapted contaminants.

The growth/no growth responses of Listeria monocytogenes inoculated at four levels (0.90, 2.58, 4.20 and 6.81 log cfu/well; 300 microl medium/well) into tryptic soy broth (TSB) were monitored at different combinations of temperature (4 to 30 degrees C), pH (3.76 to 6.44) and aw (0.888 to 0.997) for 60 days. The study was conducted in 96-well microtiter plates and growth was monitored visually and by recording the turbidity of the medium with an automated microplate reader. The growth limits of the pathogen and hence the position of the growth boundary were found to be affected by the size of the inoculum. For example, at 25 degrees C and aw 0.997 the minimum pH values that allowed growth were 4.45 and 3.94 for inoculum levels of 0.90 and 6.81 log cfu/well, respectively. Similarly, at 25 degrees C and pH 6.44 the minimum aw values where growth was observed ranged from 0.900 to 0.928 depending on the inoculum level. The results showed that at temperatures from 10 to 30 degrees C the difference in the growth limits between the tested inoculum levels was higher in environments where a single factor (pH or aw) was inhibitory than in environments where pH and aw together were inhibitory. The data were used to develop a growth/no growth interface model for each inoculum level tested, using logistic polynomial regression. The concordance indices of the models ranged from 99.8% to 99.9% and showed a good fit to the observed data in all models. This study indicates the importance of inoculum size for microbial growth initiation and provides quantitative data that show how the combinations of hurdles which prevent growth vary with inoculum size.

The effect of a simulated gastric fluid (adjusted to pH 1.0 with HCl) on Listeria monocytogenes, inoculated postprocessing on pork frankfurters formulated with sodium lactate (SL) and sodium diacetate (SD) and not dipped or dipped in solutions of lactic acid or acetic acid, was evaluated during storage of the frankfurters at 10 degrees C for 40 days. Pork frankfurters containing 1.8% SL, 0.25% SD, 1.8% SL+0.125% SD, or 1.8% SL+0.25% SD were inoculated with 10(2)-10(3) CFU/cm2 of a 10-strain preparation of L. monocytogenes and were not dipped or dipped for 2 min in solutions of 2.5% lactic or acetic acid before they were vacuum-packaged and stored. Survival of L. monocytogenes was determined after exposure of frankfurters for 0, 20, 40, and 60 min to the simulated gastric fluid after storage for 0, 10, 20, 30, or 40 days. Growth of L. monocytogenes on frankfurters formulated with antimicrobials was inhibited in the order control

Inactivation of Escherichia coli O157:H7 was evaluated on inoculated apple slices without pretreatment or pretreated by immersing in water or acid solutions commonly used to help retain apple color during dehydration, then stored at ambient temperature or dried for 6 h. Half-ring slices (0.6 cm thick) of peeled and cored Gala apples were inoculated by immersion for 30 min in a three-strain composite inoculum of E. coli O157:H7 (7.8-8.0 CFU/g). Inoculated slices received (1) no pre-drying treatment (control); or a 10-min immersion in solutions of (2) sterile water, (3) 2.8% ascorbic acid, (4) 1.7% citric acid, (5) 50% commercial lemon juice, or (6) 50% commercial lemon juice with preservatives. Drained slices were placed in sterile plastic bags and stored at room temperature (25+/-2 degrees C) for up to 6 h or dehydrated (62.8 degrees C) for up to 6 h. Samples were plated on tryptic soy agar (TSA) and sorbitol MacConkey agar (SMAC) for direct enumeration of surviving bacteria at various time intervals. Immersion in sterile water or acidic solutions caused initial bacterial reductions of 0.9-1.3 log CFU/g on apple slices. Between 0 and 6 h of storage at room temperature, slices dipped in acidic solutions showed minor changes in bacterial populations (-0.2 to +0.6 log CFU/g) compared to a 1.1 log CFU/g increase for slices dipped in sterile water. The no treatment samples (control) showed an increase in bacterial populations of 1.3-1.5 CFU/g over the 6-h holding time. For apple slices dried at 62.8 degrees C, bacterial populations were reduced by 2.5 (SMAC) and 3.1 (TSA) log CFU/g in the control (no pre-drying treatment) samples following 6 h dehydration. The slices immersed in sterile water showed a 5.8 (SMAC) and 5.1 (TSA) reduction after 6 h of dehydration. In contrast, after 6 h of dehydration bacterial populations on the four acid-pretreated products were reduced by 6.7-7.3 log CFU/g. The results showed that acidic treatment alone was not effective in destroying E. coli O157:H7 on apple slices but did inhibit growth of the organism during holding before drying. However, pretreatment of the apple slices with common household acidulants enhanced destruction of E. coli O157:H7 during drying compared to slices dried without treatment.

This study evaluated survival/growth of acid-adapted or nonadapted Escherichia coli O157:H7 inoculated (4 log CFU/wound) in wounds (10 mm deepx6 mm diameter) of apples. Wounds were inoculated with a green fluorescent protein (GFP)-expressing derivative of a rifampicin-resistant strain of E. coli O157:H7 ATCC 43895 and allowed to attach (1 h). Apples were dipped (2 min) in solutions (approximately 25 degrees C) of water (W), 5% acetic acid (AA), 5% hydrogen peroxide (HP), 0.02% sodium hypochlorite (SH), or not treated (NT), and stored at 25 degrees C. Survivors were determined in cores (10-mm deep) of the apple wounds (12 mm from center of wound; inner core) and surrounding tissue (18 mm from center of wound; outer core) after homogenizing the samples in Dey-Engley (D/E) neutralizing broth and plating on tryptic soy agar (TSA) and TSA supplemented with 100 microg/ml rifampicin (35 degrees C, 48 h) after 0, 2 and 5 days. Average bacterial populations at day-0 were 4.0 and 2.0 logs in the inner and outer core, respectively. In the inner core of the untreated apples populations increased to 7.0 logs at day-2, while counts did not exceed 3.0 logs in the outer core during storage of all treatments. Previous acid-adaptation of the cultures did not affect survival of the pathogen. Dipping in W, AA and SH did not reduce initial bacterial populations, while at day-2 of storage inner core counts from W, AA and SH reached 7.1, 5.5 and 6.9 logs, respectively. In contrast, HP reduced initial counts in the inner core by approximately 1.5 logs, but they increased to 7.0 logs by day-2. Populations of all treatments reached 6.6-7.2 logs in the inner core by day-5. Thus, sanitizer treatment did not effectively reduce nor inhibit growth of E. coli O157:H7 contamination in apple wounds and surrounding tissue.

This study evaluated the influence of pre-drying marinade treatments on inactivation of acid-adapted or nonadapted Salmonella on beef jerky during preparation, drying and storage. The inoculated (five-strain composite, 6.0 log CFU/cm2) slices were subjected to the following marinades (24 h, 4 degrees C) prior to drying at 60 degrees C for 10 h and aerobic storage at 25 degrees C for 60 days: (1) no marinade, control (C), (2) traditional marinade (TM), (3) double amount of TM modified with added 1.2% sodium lactate, 9% acetic acid, and 68% soy sauce with 5% ethanol (MM), (4) dipping into 5% acetic acid and then TM (AATM), and (5) dipping into 1% Tween 20 and then into 5% acetic acid, followed by TM (TWTM). Bacterial survivors were determined on tryptic soy agar with 0.1% pyruvate and xylose-lysine-tergitol 4 (XLT4) agar. Results indicated that drying reduced bacterial populations in the order of pre-drying treatments TWTM (4.8-6.0 log CFU/cm2)> or =AATM> or =MM>TM> or =C (2.6-5.0 log CFU/cm2). Nonadapted Salmonella were significantly (P<0.05) more resistant to inactivation during drying than acid-adapted Salmonella in all treatments. Bacterial populations decreased below the detection limit (-0.4 log CFU/cm2) as early as 7 h during drying or remained detectable even after 60 days of storage, depending on acid adaptation, pre-drying treatment, and agar media. The results indicated that acid adaptation may not cause increased resistance of Salmonella to the microbial hurdles involved in jerky processing and that use of modified marinades in manufacturing jerky may improve the effectiveness of drying in inactivating Salmonella.

The objective of the present study was to investigate the survival of acid-adapted and nonadapted Listeria monocytogenes inoculated post-drying on dried beef slices (beef jerky), which were treated (24 h, 4 degrees C) with the following marinades before drying at 60 degrees C for 10 h: (1) control (C), (2) traditional marinade (TM), (3) modified marinade; double the amount of TM with added 1.2% sodium lactate, 9% acetic acid, and 68% soy sauce with 5% ethanol (MM), (4) dipping into 5% acetic acid and then TM (AATM), and (5) dipping into 1% Tween 20 and then into 5% acetic acid followed by the TM (TWTM). Dried meat slices were inoculated with acid-adapted or nonadapted L. monocytogenes (ca. 5.7 log CFU/cm(2)) prior to aerobic storage at 25 degrees C for 60 days. Survivors were determined using tryptic soy agar with 0.1% pyruvate (TSAP) and PALCAM agar. Results showed that surviving bacterial populations on TWTM, AATM, and MM treatments were significantly (P<0.05) lower than those surviving on C and TM until 42 days of storage. By the end of 60 days of storage, bacterial populations in all treatments were not different regardless of acid adaptation or recovery media, except for treatment C inoculated with nonadapted cultures, which had significantly higher TSAP counts than other treatments. There was no significant (P> or =0.05) difference in survival of previously acid-adapted and nonadapted bacterial populations in samples of TWTM, AATM, and MM treatments. However, bacterial populations that were nonadapted were significantly higher than those that were acid-adapted on products of C and TM treatments on days 60 and 24, respectively. The earliest complete elimination (enrichment negative) of the pathogen occurred by day 28 (AATM) in products inoculated with acid-adapted cultures and by day 42 (TWTM and AATM) in products inoculated with nonadapted cultures. These results indicate that use of modified marinades in jerky processing and low water activity provided antimicrobial effects against possible post-processing contamination with L. monocytogenes.

Increased consumer awareness and concern about microbial foodborne diseases has resulted in intensified efforts to reduce contamination of raw meat, as evidenced by new meat and poultry inspection regulations being implemented in the United States. In addition to requiring operation of meat and poultry slaughtering and processing plants under the principles of the hazard analysis critical control point (HACCP) system, the new regulations have established microbiological testing criteria for Escherichia coli and Salmonella, as a means of evaluating plant performance. These developments have renewed and intensified interest in the development and commercial application of meat and poultry decontamination procedures. Technologies developed and evaluated for decontamination include live animal cleaning/washing, chemical dehairing, carcass knife-trimming to remove physical contaminants, steam/hot water-vacuuming for spot-cleaning/decontamination of carcasses, spray washing/rinsing of carcasses with water of low or high pressures and temperatures or chemical solutions, and exposure of carcass sides to pressurized steam. Under appropriate conditions, the technologies applied to carcasses may reduce mean microbiological counts by approximately one-three log colony forming units (cfu)/cm2, and some of them have been approved and are employed in commercial applications (i.e., steam-vacuuming; carcass spray-washing with water, chlorine, organic acid or trisodium phosphate solutions; hot water deluging/spraying/rinsing, and pressurized steam). The contribution of these decontamination technologies to the enhancement of food safety will be determined over the long term, as surveillance data on microbial foodborne illness are collected. This review examines carcass decontamination technologies, other than organic acids, with emphasis placed on recent advances and commercial applications.

Changes in the composition and properties of certain foods, as well as development of food products to meet consumer demands relating to health, nutrition and convenience lead to concerns about the microbiological safety of such products. Concerns also arise from emergence or recognition of the importance of certain microbial food pathogens or spoilage organisms, as well as from modifications in food processing, handling, storage and preparation procedures. These facts necessitate continuous reevaluation of factors involved in the control of microbial growth in order to preserve foods and maintain their quality and safety.

The effect of sodium lactate (1.8% w/w), sodium erythorbate (0.1% w/w), kappa-carrageenan (1% w/w), and the alginate meat binder (0.4% w/w, sodium alginate; 0.6% w/w lactic acid; and 0.075% w/w calcium carbonate) on Listeria monocytogenes survival and growth was determined in raw and cooked ground beef stored aerobically at 4 degrees C. There was no significant (P > 0.05) increase in numbers of L. monocytogenes during storage of raw ground beef. However, L. monocytogenes numbers were generally lower in treatments with sodium lactate, and higher in sodium erythorbate compared to controls and meat with other additives. Increases in total aerobic plate counts were less pronounced in raw meat formulated with sodium lactate and alginate meat binder than with other additives. Cooking meat with initial inoculum levels of 6.52 to 7.03 L. monocytogenes log CFU/g to 65 degrees C resulted in lower destruction (0.56 and 1.18 log CFU/g) in samples with added alginate meat binder and kappa-carrageenan, respectively, compared to the control. Survivors (2.11-3.73 log CFU/g) decreased initially and then increased slightly, but not significantly (P > 0.05), during storage (4 degrees C, 6 days) of the cooked products.

This study examined the potential for injury of Bacillus globigii (Bacillus subtilis var. niger, strain ATCC9372) spores during extrusion cooking of a corn/soybean (70/30%, w/v) mixture. The barrel temperature in zone 1 was kept constant at 80 degrees C while it was varied from 100 to 120 and 140 degrees C in zone 2. Recovery and enumeration of spores surviving the extrusion cooking process were conducted with five culture media ranging from minimal to rich in nutrient composition. Numbers of spores counted with a minimal culture medium after extrusion at the low temperature were lower compared to recovery with more complete media. All culture media, including minimal and richer, were equally effective in recovering untreated spores. At the higher extrusion temperatures all media were equally effective in recovering the small numbers of viable spores. The results indicated that the spores of the organism may be injured at lower extrusion temperatures.